Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+==========================
+BFQ (Budget Fair Queueing)
+==========================
+
+BFQ is a proportional-share I/O scheduler, with some extra
+low-latency capabilities. In addition to cgroups support (blkio or io
+controllers), BFQ's main features are:
+
+- BFQ guarantees a high system and application responsiveness, and a
+  low latency for time-sensitive applications, such as audio or video
+  players;
+- BFQ distributes bandwidth, and not just time, among processes or
+  groups (switching back to time distribution when needed to keep
+  throughput high).
+
+In its default configuration, BFQ privileges latency over
+throughput. So, when needed for achieving a lower latency, BFQ builds
+schedules that may lead to a lower throughput. If your main or only
+goal, for a given device, is to achieve the maximum-possible
+throughput at all times, then do switch off all low-latency heuristics
+for that device, by setting low_latency to 0. See Section 3 for
+details on how to configure BFQ for the desired tradeoff between
+latency and throughput, or on how to maximize throughput.
+
+As every I/O scheduler, BFQ adds some overhead to per-I/O-request
+processing. To give an idea of this overhead, the total,
+single-lock-protected, per-request processing time of BFQ---i.e., the
+sum of the execution times of the request insertion, dispatch and
+completion hooks---is, e.g., 1.9 us on an Intel Core i7-2760QM@2.40GHz
+(dated CPU for notebooks; time measured with simple code
+instrumentation, and using the throughput-sync.sh script of the S
+suite [1], in performance-profiling mode). To put this result into
+context, the total, single-lock-protected, per-request execution time
+of the lightest I/O scheduler available in blk-mq, mq-deadline, is 0.7
+us (mq-deadline is ~800 LOC, against ~10500 LOC for BFQ).
+
+Scheduling overhead further limits the maximum IOPS that a CPU can
+process (already limited by the execution of the rest of the I/O
+stack). To give an idea of the limits with BFQ, on slow or average
+CPUs, here are, first, the limits of BFQ for three different CPUs, on,
+respectively, an average laptop, an old desktop, and a cheap embedded
+system, in case full hierarchical support is enabled (i.e.,
+CONFIG_BFQ_GROUP_IOSCHED is set), but CONFIG_BFQ_CGROUP_DEBUG is not
+set (Section 4-2):
+- Intel i7-4850HQ: 400 KIOPS
+- AMD A8-3850: 250 KIOPS
+- ARM CortexTM-A53 Octa-core: 80 KIOPS
+
+If CONFIG_BFQ_CGROUP_DEBUG is set (and of course full hierarchical
+support is enabled), then the sustainable throughput with BFQ
+decreases, because all blkio.bfq* statistics are created and updated
+(Section 4-2). For BFQ, this leads to the following maximum
+sustainable throughputs, on the same systems as above:
+- Intel i7-4850HQ: 310 KIOPS
+- AMD A8-3850: 200 KIOPS
+- ARM CortexTM-A53 Octa-core: 56 KIOPS
+
+BFQ works for multi-queue devices too.
+
+.. The table of contents follow. Impatients can just jump to Section 3.
+
+.. CONTENTS
+
+   1. When may BFQ be useful?
+    1-1 Personal systems
+    1-2 Server systems
+   2. How does BFQ work?
+   3. What are BFQ's tunables and how to properly configure BFQ?
+   4. BFQ group scheduling
+    4-1 Service guarantees provided
+    4-2 Interface
+
+1. When may BFQ be useful?
+==========================
+
+BFQ provides the following benefits on personal and server systems.
+
+1-1 Personal systems
+--------------------
+
+Low latency for interactive applications
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Regardless of the actual background workload, BFQ guarantees that, for
+interactive tasks, the storage device is virtually as responsive as if
+it was idle. For example, even if one or more of the following
+background workloads are being executed:
+
+- one or more large files are being read, written or copied,
+- a tree of source files is being compiled,
+- one or more virtual machines are performing I/O,
+- a software update is in progress,
+- indexing daemons are scanning filesystems and updating their
+  databases,
+
+starting an application or loading a file from within an application
+takes about the same time as if the storage device was idle. As a
+comparison, with CFQ, NOOP or DEADLINE, and in the same conditions,
+applications experience high latencies, or even become unresponsive
+until the background workload terminates (also on SSDs).
+
+Low latency for soft real-time applications
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Also soft real-time applications, such as audio and video
+players/streamers, enjoy a low latency and a low drop rate, regardless
+of the background I/O workload. As a consequence, these applications
+do not suffer from almost any glitch due to the background workload.
+
+Higher speed for code-development tasks
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If some additional workload happens to be executed in parallel, then
+BFQ executes the I/O-related components of typical code-development
+tasks (compilation, checkout, merge, ...) much more quickly than CFQ,
+NOOP or DEADLINE.
+
+High throughput
+^^^^^^^^^^^^^^^
+
+On hard disks, BFQ achieves up to 30% higher throughput than CFQ, and
+up to 150% higher throughput than DEADLINE and NOOP, with all the
+sequential workloads considered in our tests. With random workloads,
+and with all the workloads on flash-based devices, BFQ achieves,
+instead, about the same throughput as the other schedulers.
+
+Strong fairness, bandwidth and delay guarantees
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+BFQ distributes the device throughput, and not just the device time,
+among I/O-bound applications in proportion their weights, with any
+workload and regardless of the device parameters. From these bandwidth
+guarantees, it is possible to compute tight per-I/O-request delay
+guarantees by a simple formula. If not configured for strict service
+guarantees, BFQ switches to time-based resource sharing (only) for
+applications that would otherwise cause a throughput loss.
+
+1-2 Server systems
+------------------
+
+Most benefits for server systems follow from the same service
+properties as above. In particular, regardless of whether additional,
+possibly heavy workloads are being served, BFQ guarantees:
+
+* audio and video-streaming with zero or very low jitter and drop
+  rate;
+
+* fast retrieval of WEB pages and embedded objects;
+
+* real-time recording of data in live-dumping applications (e.g.,
+  packet logging);
+
+* responsiveness in local and remote access to a server.
+
+
+2. How does BFQ work?
+=====================
+
+BFQ is a proportional-share I/O scheduler, whose general structure,
+plus a lot of code, are borrowed from CFQ.
+
+- Each process doing I/O on a device is associated with a weight and a
+  `(bfq_)queue`.
+
+- BFQ grants exclusive access to the device, for a while, to one queue
+  (process) at a time, and implements this service model by
+  associating every queue with a budget, measured in number of
+  sectors.
+
+  - After a queue is granted access to the device, the budget of the
+    queue is decremented, on each request dispatch, by the size of the
+    request.
+
+  - The in-service queue is expired, i.e., its service is suspended,
+    only if one of the following events occurs: 1) the queue finishes
+    its budget, 2) the queue empties, 3) a "budget timeout" fires.
+
+    - The budget timeout prevents processes doing random I/O from
+      holding the device for too long and dramatically reducing
+      throughput.
+
+    - Actually, as in CFQ, a queue associated with a process issuing
+      sync requests may not be expired immediately when it empties. In
+      contrast, BFQ may idle the device for a short time interval,
+      giving the process the chance to go on being served if it issues
+      a new request in time. Device idling typically boosts the
+      throughput on rotational devices and on non-queueing flash-based
+      devices, if processes do synchronous and sequential I/O. In
+      addition, under BFQ, device idling is also instrumental in
+      guaranteeing the desired throughput fraction to processes
+      issuing sync requests (see the description of the slice_idle
+      tunable in this document, or [1, 2], for more details).
+
+      - With respect to idling for service guarantees, if several
+	processes are competing for the device at the same time, but
+	all processes and groups have the same weight, then BFQ
+	guarantees the expected throughput distribution without ever
+	idling the device. Throughput is thus as high as possible in
+	this common scenario.
+
+     - On flash-based storage with internal queueing of commands
+       (typically NCQ), device idling happens to be always detrimental
+       for throughput. So, with these devices, BFQ performs idling
+       only when strictly needed for service guarantees, i.e., for
+       guaranteeing low latency or fairness. In these cases, overall
+       throughput may be sub-optimal. No solution currently exists to
+       provide both strong service guarantees and optimal throughput
+       on devices with internal queueing.
+
+  - If low-latency mode is enabled (default configuration), BFQ
+    executes some special heuristics to detect interactive and soft
+    real-time applications (e.g., video or audio players/streamers),
+    and to reduce their latency. The most important action taken to
+    achieve this goal is to give to the queues associated with these
+    applications more than their fair share of the device
+    throughput. For brevity, we call just "weight-raising" the whole
+    sets of actions taken by BFQ to privilege these queues. In
+    particular, BFQ provides a milder form of weight-raising for
+    interactive applications, and a stronger form for soft real-time
+    applications.
+
+  - BFQ automatically deactivates idling for queues born in a burst of
+    queue creations. In fact, these queues are usually associated with
+    the processes of applications and services that benefit mostly
+    from a high throughput. Examples are systemd during boot, or git
+    grep.
+
+  - As CFQ, BFQ merges queues performing interleaved I/O, i.e.,
+    performing random I/O that becomes mostly sequential if
+    merged. Differently from CFQ, BFQ achieves this goal with a more
+    reactive mechanism, called Early Queue Merge (EQM). EQM is so
+    responsive in detecting interleaved I/O (cooperating processes),
+    that it enables BFQ to achieve a high throughput, by queue
+    merging, even for queues for which CFQ needs a different
+    mechanism, preemption, to get a high throughput. As such EQM is a
+    unified mechanism to achieve a high throughput with interleaved
+    I/O.
+
+  - Queues are scheduled according to a variant of WF2Q+, named
+    B-WF2Q+, and implemented using an augmented rb-tree to preserve an
+    O(log N) overall complexity.  See [2] for more details. B-WF2Q+ is
+    also ready for hierarchical scheduling, details in Section 4.
+
+  - B-WF2Q+ guarantees a tight deviation with respect to an ideal,
+    perfectly fair, and smooth service. In particular, B-WF2Q+
+    guarantees that each queue receives a fraction of the device
+    throughput proportional to its weight, even if the throughput
+    fluctuates, and regardless of: the device parameters, the current
+    workload and the budgets assigned to the queue.
+
+  - The last, budget-independence, property (although probably
+    counterintuitive in the first place) is definitely beneficial, for
+    the following reasons:
+
+    - First, with any proportional-share scheduler, the maximum
+      deviation with respect to an ideal service is proportional to
+      the maximum budget (slice) assigned to queues. As a consequence,
+      BFQ can keep this deviation tight not only because of the
+      accurate service of B-WF2Q+, but also because BFQ *does not*
+      need to assign a larger budget to a queue to let the queue
+      receive a higher fraction of the device throughput.
+
+    - Second, BFQ is free to choose, for every process (queue), the
+      budget that best fits the needs of the process, or best
+      leverages the I/O pattern of the process. In particular, BFQ
+      updates queue budgets with a simple feedback-loop algorithm that
+      allows a high throughput to be achieved, while still providing
+      tight latency guarantees to time-sensitive applications. When
+      the in-service queue expires, this algorithm computes the next
+      budget of the queue so as to:
+
+      - Let large budgets be eventually assigned to the queues
+	associated with I/O-bound applications performing sequential
+	I/O: in fact, the longer these applications are served once
+	got access to the device, the higher the throughput is.
+
+      - Let small budgets be eventually assigned to the queues
+	associated with time-sensitive applications (which typically
+	perform sporadic and short I/O), because, the smaller the
+	budget assigned to a queue waiting for service is, the sooner
+	B-WF2Q+ will serve that queue (Subsec 3.3 in [2]).
+
+- If several processes are competing for the device at the same time,
+  but all processes and groups have the same weight, then BFQ
+  guarantees the expected throughput distribution without ever idling
+  the device. It uses preemption instead. Throughput is then much
+  higher in this common scenario.
+
+- ioprio classes are served in strict priority order, i.e.,
+  lower-priority queues are not served as long as there are
+  higher-priority queues.  Among queues in the same class, the
+  bandwidth is distributed in proportion to the weight of each
+  queue. A very thin extra bandwidth is however guaranteed to
+  the Idle class, to prevent it from starving.
+
+
+3. What are BFQ's tunables and how to properly configure BFQ?
+=============================================================
+
+Most BFQ tunables affect service guarantees (basically latency and
+fairness) and throughput. For full details on how to choose the
+desired tradeoff between service guarantees and throughput, see the
+parameters slice_idle, strict_guarantees and low_latency. For details
+on how to maximise throughput, see slice_idle, timeout_sync and
+max_budget. The other performance-related parameters have been
+inherited from, and have been preserved mostly for compatibility with
+CFQ. So far, no performance improvement has been reported after
+changing the latter parameters in BFQ.
+
+In particular, the tunables back_seek-max, back_seek_penalty,
+fifo_expire_async and fifo_expire_sync below are the same as in
+CFQ. Their description is just copied from that for CFQ. Some
+considerations in the description of slice_idle are copied from CFQ
+too.
+
+per-process ioprio and weight
+-----------------------------
+
+Unless the cgroups interface is used (see "4. BFQ group scheduling"),
+weights can be assigned to processes only indirectly, through I/O
+priorities, and according to the relation:
+weight = (IOPRIO_BE_NR - ioprio) * 10.
+
+Beware that, if low-latency is set, then BFQ automatically raises the
+weight of the queues associated with interactive and soft real-time
+applications. Unset this tunable if you need/want to control weights.
+
+slice_idle
+----------
+
+This parameter specifies how long BFQ should idle for next I/O
+request, when certain sync BFQ queues become empty. By default
+slice_idle is a non-zero value. Idling has a double purpose: boosting
+throughput and making sure that the desired throughput distribution is
+respected (see the description of how BFQ works, and, if needed, the
+papers referred there).
+
+As for throughput, idling can be very helpful on highly seeky media
+like single spindle SATA/SAS disks where we can cut down on overall
+number of seeks and see improved throughput.
+
+Setting slice_idle to 0 will remove all the idling on queues and one
+should see an overall improved throughput on faster storage devices
+like multiple SATA/SAS disks in hardware RAID configuration, as well
+as flash-based storage with internal command queueing (and
+parallelism).
+
+So depending on storage and workload, it might be useful to set
+slice_idle=0.  In general for SATA/SAS disks and software RAID of
+SATA/SAS disks keeping slice_idle enabled should be useful. For any
+configurations where there are multiple spindles behind single LUN
+(Host based hardware RAID controller or for storage arrays), or with
+flash-based fast storage, setting slice_idle=0 might end up in better
+throughput and acceptable latencies.
+
+Idling is however necessary to have service guarantees enforced in
+case of differentiated weights or differentiated I/O-request lengths.
+To see why, suppose that a given BFQ queue A must get several I/O
+requests served for each request served for another queue B. Idling
+ensures that, if A makes a new I/O request slightly after becoming
+empty, then no request of B is dispatched in the middle, and thus A
+does not lose the possibility to get more than one request dispatched
+before the next request of B is dispatched. Note that idling
+guarantees the desired differentiated treatment of queues only in
+terms of I/O-request dispatches. To guarantee that the actual service
+order then corresponds to the dispatch order, the strict_guarantees
+tunable must be set too.
+
+There is an important flipside for idling: apart from the above cases
+where it is beneficial also for throughput, idling can severely impact
+throughput. One important case is random workload. Because of this
+issue, BFQ tends to avoid idling as much as possible, when it is not
+beneficial also for throughput (as detailed in Section 2). As a
+consequence of this behavior, and of further issues described for the
+strict_guarantees tunable, short-term service guarantees may be
+occasionally violated. And, in some cases, these guarantees may be
+more important than guaranteeing maximum throughput. For example, in
+video playing/streaming, a very low drop rate may be more important
+than maximum throughput. In these cases, consider setting the
+strict_guarantees parameter.
+
+slice_idle_us
+-------------
+
+Controls the same tuning parameter as slice_idle, but in microseconds.
+Either tunable can be used to set idling behavior.  Afterwards, the
+other tunable will reflect the newly set value in sysfs.
+
+strict_guarantees
+-----------------
+
+If this parameter is set (default: unset), then BFQ
+
+- always performs idling when the in-service queue becomes empty;
+
+- forces the device to serve one I/O request at a time, by dispatching a
+  new request only if there is no outstanding request.
+
+In the presence of differentiated weights or I/O-request sizes, both
+the above conditions are needed to guarantee that every BFQ queue
+receives its allotted share of the bandwidth. The first condition is
+needed for the reasons explained in the description of the slice_idle
+tunable.  The second condition is needed because all modern storage
+devices reorder internally-queued requests, which may trivially break
+the service guarantees enforced by the I/O scheduler.
+
+Setting strict_guarantees may evidently affect throughput.
+
+back_seek_max
+-------------
+
+This specifies, given in Kbytes, the maximum "distance" for backward seeking.
+The distance is the amount of space from the current head location to the
+sectors that are backward in terms of distance.
+
+This parameter allows the scheduler to anticipate requests in the "backward"
+direction and consider them as being the "next" if they are within this
+distance from the current head location.
+
+back_seek_penalty
+-----------------
+
+This parameter is used to compute the cost of backward seeking. If the
+backward distance of request is just 1/back_seek_penalty from a "front"
+request, then the seeking cost of two requests is considered equivalent.
+
+So scheduler will not bias toward one or the other request (otherwise scheduler
+will bias toward front request). Default value of back_seek_penalty is 2.
+
+fifo_expire_async
+-----------------
+
+This parameter is used to set the timeout of asynchronous requests. Default
+value of this is 250ms.
+
+fifo_expire_sync
+----------------
+
+This parameter is used to set the timeout of synchronous requests. Default
+value of this is 125ms. In case to favor synchronous requests over asynchronous
+one, this value should be decreased relative to fifo_expire_async.
+
+low_latency
+-----------
+
+This parameter is used to enable/disable BFQ's low latency mode. By
+default, low latency mode is enabled. If enabled, interactive and soft
+real-time applications are privileged and experience a lower latency,
+as explained in more detail in the description of how BFQ works.
+
+DISABLE this mode if you need full control on bandwidth
+distribution. In fact, if it is enabled, then BFQ automatically
+increases the bandwidth share of privileged applications, as the main
+means to guarantee a lower latency to them.
+
+In addition, as already highlighted at the beginning of this document,
+DISABLE this mode if your only goal is to achieve a high throughput.
+In fact, privileging the I/O of some application over the rest may
+entail a lower throughput. To achieve the highest-possible throughput
+on a non-rotational device, setting slice_idle to 0 may be needed too
+(at the cost of giving up any strong guarantee on fairness and low
+latency).
+
+timeout_sync
+------------
+
+Maximum amount of device time that can be given to a task (queue) once
+it has been selected for service. On devices with costly seeks,
+increasing this time usually increases maximum throughput. On the
+opposite end, increasing this time coarsens the granularity of the
+short-term bandwidth and latency guarantees, especially if the
+following parameter is set to zero.
+
+max_budget
+----------
+
+Maximum amount of service, measured in sectors, that can be provided
+to a BFQ queue once it is set in service (of course within the limits
+of the above timeout). According to what said in the description of
+the algorithm, larger values increase the throughput in proportion to
+the percentage of sequential I/O requests issued. The price of larger
+values is that they coarsen the granularity of short-term bandwidth
+and latency guarantees.
+
+The default value is 0, which enables auto-tuning: BFQ sets max_budget
+to the maximum number of sectors that can be served during
+timeout_sync, according to the estimated peak rate.
+
+For specific devices, some users have occasionally reported to have
+reached a higher throughput by setting max_budget explicitly, i.e., by
+setting max_budget to a higher value than 0. In particular, they have
+set max_budget to higher values than those to which BFQ would have set
+it with auto-tuning. An alternative way to achieve this goal is to
+just increase the value of timeout_sync, leaving max_budget equal to 0.
+
+4. Group scheduling with BFQ
+============================
+
+BFQ supports both cgroups-v1 and cgroups-v2 io controllers, namely
+blkio and io. In particular, BFQ supports weight-based proportional
+share. To activate cgroups support, set BFQ_GROUP_IOSCHED.
+
+4-1 Service guarantees provided
+-------------------------------
+
+With BFQ, proportional share means true proportional share of the
+device bandwidth, according to group weights. For example, a group
+with weight 200 gets twice the bandwidth, and not just twice the time,
+of a group with weight 100.
+
+BFQ supports hierarchies (group trees) of any depth. Bandwidth is
+distributed among groups and processes in the expected way: for each
+group, the children of the group share the whole bandwidth of the
+group in proportion to their weights. In particular, this implies
+that, for each leaf group, every process of the group receives the
+same share of the whole group bandwidth, unless the ioprio of the
+process is modified.
+
+The resource-sharing guarantee for a group may partially or totally
+switch from bandwidth to time, if providing bandwidth guarantees to
+the group lowers the throughput too much. This switch occurs on a
+per-process basis: if a process of a leaf group causes throughput loss
+if served in such a way to receive its share of the bandwidth, then
+BFQ switches back to just time-based proportional share for that
+process.
+
+4-2 Interface
+-------------
+
+To get proportional sharing of bandwidth with BFQ for a given device,
+BFQ must of course be the active scheduler for that device.
+
+Within each group directory, the names of the files associated with
+BFQ-specific cgroup parameters and stats begin with the "bfq."
+prefix. So, with cgroups-v1 or cgroups-v2, the full prefix for
+BFQ-specific files is "blkio.bfq." or "io.bfq." For example, the group
+parameter to set the weight of a group with BFQ is blkio.bfq.weight
+or io.bfq.weight.
+
+As for cgroups-v1 (blkio controller), the exact set of stat files
+created, and kept up-to-date by bfq, depends on whether
+CONFIG_BFQ_CGROUP_DEBUG is set. If it is set, then bfq creates all
+the stat files documented in
+Documentation/admin-guide/cgroup-v1/blkio-controller.rst. If, instead,
+CONFIG_BFQ_CGROUP_DEBUG is not set, then bfq creates only the files::
+
+  blkio.bfq.io_service_bytes
+  blkio.bfq.io_service_bytes_recursive
+  blkio.bfq.io_serviced
+  blkio.bfq.io_serviced_recursive
+
+The value of CONFIG_BFQ_CGROUP_DEBUG greatly influences the maximum
+throughput sustainable with bfq, because updating the blkio.bfq.*
+stats is rather costly, especially for some of the stats enabled by
+CONFIG_BFQ_CGROUP_DEBUG.
+
+Parameters
+----------
+
+For each group, the following parameters can be set:
+
+  weight
+        This specifies the default weight for the cgroup inside its parent.
+        Available values: 1..1000 (default: 100).
+
+        For cgroup v1, it is set by writing the value to `blkio.bfq.weight`.
+
+        For cgroup v2, it is set by writing the value to `io.bfq.weight`.
+        (with an optional prefix of `default` and a space).
+
+        The linear mapping between ioprio and weights, described at the beginning
+        of the tunable section, is still valid, but all weights higher than
+        IOPRIO_BE_NR*10 are mapped to ioprio 0.
+
+        Recall that, if low-latency is set, then BFQ automatically raises the
+        weight of the queues associated with interactive and soft real-time
+        applications. Unset this tunable if you need/want to control weights.
+
+  weight_device
+        This specifies a per-device weight for the cgroup. The syntax is
+        `minor:major weight`. A weight of `0` may be used to reset to the default
+        weight.
+
+        For cgroup v1, it is set by writing the value to `blkio.bfq.weight_device`.
+
+        For cgroup v2, the file name is `io.bfq.weight`.
+
+
+[1]
+    P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O
+    Scheduler", Proceedings of the First Workshop on Mobile System
+    Technologies (MST-2015), May 2015.
+
+    http://algogroup.unimore.it/people/paolo/disk_sched/mst-2015.pdf
+
+[2]
+    P. Valente and M. Andreolini, "Improving Application
+    Responsiveness with the BFQ Disk I/O Scheduler", Proceedings of
+    the 5th Annual International Systems and Storage Conference
+    (SYSTOR '12), June 2012.
+
+    Slightly extended version:
+
+    http://algogroup.unimore.it/people/paolo/disk_sched/bfq-v1-suite-results.pdf
+
+[3]
+   https://github.com/Algodev-github/S
diff --git a/Documentation/block/biovecs.rst b/Documentation/block/biovecs.rst
new file mode 100644
index 000000000..ddb867e01
--- /dev/null
+++ b/Documentation/block/biovecs.rst
@@ -0,0 +1,150 @@
+======================================
+Immutable biovecs and biovec iterators
+======================================
+
+Kent Overstreet <kmo@daterainc.com>
+
+As of 3.13, biovecs should never be modified after a bio has been submitted.
+Instead, we have a new struct bvec_iter which represents a range of a biovec -
+the iterator will be modified as the bio is completed, not the biovec.
+
+More specifically, old code that needed to partially complete a bio would
+update bi_sector and bi_size, and advance bi_idx to the next biovec. If it
+ended up partway through a biovec, it would increment bv_offset and decrement
+bv_len by the number of bytes completed in that biovec.
+
+In the new scheme of things, everything that must be mutated in order to
+partially complete a bio is segregated into struct bvec_iter: bi_sector,
+bi_size and bi_idx have been moved there; and instead of modifying bv_offset
+and bv_len, struct bvec_iter has bi_bvec_done, which represents the number of
+bytes completed in the current bvec.
+
+There are a bunch of new helper macros for hiding the gory details - in
+particular, presenting the illusion of partially completed biovecs so that
+normal code doesn't have to deal with bi_bvec_done.
+
+ * Driver code should no longer refer to biovecs directly; we now have
+   bio_iovec() and bio_iter_iovec() macros that return literal struct biovecs,
+   constructed from the raw biovecs but taking into account bi_bvec_done and
+   bi_size.
+
+   bio_for_each_segment() has been updated to take a bvec_iter argument
+   instead of an integer (that corresponded to bi_idx); for a lot of code the
+   conversion just required changing the types of the arguments to
+   bio_for_each_segment().
+
+ * Advancing a bvec_iter is done with bio_advance_iter(); bio_advance() is a
+   wrapper around bio_advance_iter() that operates on bio->bi_iter, and also
+   advances the bio integrity's iter if present.
+
+   There is a lower level advance function - bvec_iter_advance() - which takes
+   a pointer to a biovec, not a bio; this is used by the bio integrity code.
+
+As of 5.12 bvec segments with zero bv_len are not supported.
+
+What's all this get us?
+=======================
+
+Having a real iterator, and making biovecs immutable, has a number of
+advantages:
+
+ * Before, iterating over bios was very awkward when you weren't processing
+   exactly one bvec at a time - for example, bio_copy_data() in block/bio.c,
+   which copies the contents of one bio into another. Because the biovecs
+   wouldn't necessarily be the same size, the old code was tricky convoluted -
+   it had to walk two different bios at the same time, keeping both bi_idx and
+   and offset into the current biovec for each.
+
+   The new code is much more straightforward - have a look. This sort of
+   pattern comes up in a lot of places; a lot of drivers were essentially open
+   coding bvec iterators before, and having common implementation considerably
+   simplifies a lot of code.
+
+ * Before, any code that might need to use the biovec after the bio had been
+   completed (perhaps to copy the data somewhere else, or perhaps to resubmit
+   it somewhere else if there was an error) had to save the entire bvec array
+   - again, this was being done in a fair number of places.
+
+ * Biovecs can be shared between multiple bios - a bvec iter can represent an
+   arbitrary range of an existing biovec, both starting and ending midway
+   through biovecs. This is what enables efficient splitting of arbitrary
+   bios. Note that this means we _only_ use bi_size to determine when we've
+   reached the end of a bio, not bi_vcnt - and the bio_iovec() macro takes
+   bi_size into account when constructing biovecs.
+
+ * Splitting bios is now much simpler. The old bio_split() didn't even work on
+   bios with more than a single bvec! Now, we can efficiently split arbitrary
+   size bios - because the new bio can share the old bio's biovec.
+
+   Care must be taken to ensure the biovec isn't freed while the split bio is
+   still using it, in case the original bio completes first, though. Using
+   bio_chain() when splitting bios helps with this.
+
+ * Submitting partially completed bios is now perfectly fine - this comes up
+   occasionally in stacking block drivers and various code (e.g. md and
+   bcache) had some ugly workarounds for this.
+
+   It used to be the case that submitting a partially completed bio would work
+   fine to _most_ devices, but since accessing the raw bvec array was the
+   norm, not all drivers would respect bi_idx and those would break. Now,
+   since all drivers _must_ go through the bvec iterator - and have been
+   audited to make sure they are - submitting partially completed bios is
+   perfectly fine.
+
+Other implications:
+===================
+
+ * Almost all usage of bi_idx is now incorrect and has been removed; instead,
+   where previously you would have used bi_idx you'd now use a bvec_iter,
+   probably passing it to one of the helper macros.
+
+   I.e. instead of using bio_iovec_idx() (or bio->bi_iovec[bio->bi_idx]), you
+   now use bio_iter_iovec(), which takes a bvec_iter and returns a
+   literal struct bio_vec - constructed on the fly from the raw biovec but
+   taking into account bi_bvec_done (and bi_size).
+
+ * bi_vcnt can't be trusted or relied upon by driver code - i.e. anything that
+   doesn't actually own the bio. The reason is twofold: firstly, it's not
+   actually needed for iterating over the bio anymore - we only use bi_size.
+   Secondly, when cloning a bio and reusing (a portion of) the original bio's
+   biovec, in order to calculate bi_vcnt for the new bio we'd have to iterate
+   over all the biovecs in the new bio - which is silly as it's not needed.
+
+   So, don't use bi_vcnt anymore.
+
+ * The current interface allows the block layer to split bios as needed, so we
+   could eliminate a lot of complexity particularly in stacked drivers. Code
+   that creates bios can then create whatever size bios are convenient, and
+   more importantly stacked drivers don't have to deal with both their own bio
+   size limitations and the limitations of the underlying devices. Thus
+   there's no need to define ->merge_bvec_fn() callbacks for individual block
+   drivers.
+
+Usage of helpers:
+=================
+
+* The following helpers whose names have the suffix of `_all` can only be used
+  on non-BIO_CLONED bio. They are usually used by filesystem code. Drivers
+  shouldn't use them because the bio may have been split before it reached the
+  driver.
+
+::
+
+	bio_for_each_segment_all()
+	bio_for_each_bvec_all()
+	bio_first_bvec_all()
+	bio_first_page_all()
+	bio_last_bvec_all()
+
+* The following helpers iterate over single-page segment. The passed 'struct
+  bio_vec' will contain a single-page IO vector during the iteration::
+
+	bio_for_each_segment()
+	bio_for_each_segment_all()
+
+* The following helpers iterate over multi-page bvec. The passed 'struct
+  bio_vec' will contain a multi-page IO vector during the iteration::
+
+	bio_for_each_bvec()
+	bio_for_each_bvec_all()
+	rq_for_each_bvec()
diff --git a/Documentation/block/blk-mq.rst b/Documentation/block/blk-mq.rst
new file mode 100644
index 000000000..31f52f326
--- /dev/null
+++ b/Documentation/block/blk-mq.rst
@@ -0,0 +1,153 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+================================================
+Multi-Queue Block IO Queueing Mechanism (blk-mq)
+================================================
+
+The Multi-Queue Block IO Queueing Mechanism is an API to enable fast storage
+devices to achieve a huge number of input/output operations per second (IOPS)
+through queueing and submitting IO requests to block devices simultaneously,
+benefiting from the parallelism offered by modern storage devices.
+
+Introduction
+============
+
+Background
+----------
+
+Magnetic hard disks have been the de facto standard from the beginning of the
+development of the kernel. The Block IO subsystem aimed to achieve the best
+performance possible for those devices with a high penalty when doing random
+access, and the bottleneck was the mechanical moving parts, a lot slower than
+any layer on the storage stack. One example of such optimization technique
+involves ordering read/write requests according to the current position of the
+hard disk head.
+
+However, with the development of Solid State Drives and Non-Volatile Memories
+without mechanical parts nor random access penalty and capable of performing
+high parallel access, the bottleneck of the stack had moved from the storage
+device to the operating system. In order to take advantage of the parallelism
+in those devices' design, the multi-queue mechanism was introduced.
+
+The former design had a single queue to store block IO requests with a single
+lock. That did not scale well in SMP systems due to dirty data in cache and the
+bottleneck of having a single lock for multiple processors. This setup also
+suffered with congestion when different processes (or the same process, moving
+to different CPUs) wanted to perform block IO. Instead of this, the blk-mq API
+spawns multiple queues with individual entry points local to the CPU, removing
+the need for a lock. A deeper explanation on how this works is covered in the
+following section (`Operation`_).
+
+Operation
+---------
+
+When the userspace performs IO to a block device (reading or writing a file,
+for instance), blk-mq takes action: it will store and manage IO requests to
+the block device, acting as middleware between the userspace (and a file
+system, if present) and the block device driver.
+
+blk-mq has two group of queues: software staging queues and hardware dispatch
+queues. When the request arrives at the block layer, it will try the shortest
+path possible: send it directly to the hardware queue. However, there are two
+cases that it might not do that: if there's an IO scheduler attached at the
+layer or if we want to try to merge requests. In both cases, requests will be
+sent to the software queue.
+
+Then, after the requests are processed by software queues, they will be placed
+at the hardware queue, a second stage queue where the hardware has direct access
+to process those requests. However, if the hardware does not have enough
+resources to accept more requests, blk-mq will places requests on a temporary
+queue, to be sent in the future, when the hardware is able.
+
+Software staging queues
+~~~~~~~~~~~~~~~~~~~~~~~
+
+The block IO subsystem adds requests in the software staging queues
+(represented by struct blk_mq_ctx) in case that they weren't sent
+directly to the driver. A request is one or more BIOs. They arrived at the
+block layer through the data structure struct bio. The block layer
+will then build a new structure from it, the struct request that will
+be used to communicate with the device driver. Each queue has its own lock and
+the number of queues is defined by a per-CPU or per-node basis.
+
+The staging queue can be used to merge requests for adjacent sectors. For
+instance, requests for sector 3-6, 6-7, 7-9 can become one request for 3-9.
+Even if random access to SSDs and NVMs have the same time of response compared
+to sequential access, grouped requests for sequential access decreases the
+number of individual requests. This technique of merging requests is called
+plugging.
+
+Along with that, the requests can be reordered to ensure fairness of system
+resources (e.g. to ensure that no application suffers from starvation) and/or to
+improve IO performance, by an IO scheduler.
+
+IO Schedulers
+^^^^^^^^^^^^^
+
+There are several schedulers implemented by the block layer, each one following
+a heuristic to improve the IO performance. They are "pluggable" (as in plug
+and play), in the sense of they can be selected at run time using sysfs. You
+can read more about Linux's IO schedulers `here
+<https://www.kernel.org/doc/html/latest/block/index.html>`_. The scheduling
+happens only between requests in the same queue, so it is not possible to merge
+requests from different queues, otherwise there would be cache trashing and a
+need to have a lock for each queue. After the scheduling, the requests are
+eligible to be sent to the hardware. One of the possible schedulers to be
+selected is the NONE scheduler, the most straightforward one. It will just
+place requests on whatever software queue the process is running on, without
+any reordering. When the device starts processing requests in the hardware
+queue (a.k.a. run the hardware queue), the software queues mapped to that
+hardware queue will be drained in sequence according to their mapping.
+
+Hardware dispatch queues
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+The hardware queue (represented by struct blk_mq_hw_ctx) is a struct
+used by device drivers to map the device submission queues (or device DMA ring
+buffer), and are the last step of the block layer submission code before the
+low level device driver taking ownership of the request. To run this queue, the
+block layer removes requests from the associated software queues and tries to
+dispatch to the hardware.
+
+If it's not possible to send the requests directly to hardware, they will be
+added to a linked list (``hctx->dispatch``) of requests. Then,
+next time the block layer runs a queue, it will send the requests laying at the
+``dispatch`` list first, to ensure a fairness dispatch with those
+requests that were ready to be sent first. The number of hardware queues
+depends on the number of hardware contexts supported by the hardware and its
+device driver, but it will not be more than the number of cores of the system.
+There is no reordering at this stage, and each software queue has a set of
+hardware queues to send requests for.
+
+.. note::
+
+        Neither the block layer nor the device protocols guarantee
+        the order of completion of requests. This must be handled by
+        higher layers, like the filesystem.
+
+Tag-based completion
+~~~~~~~~~~~~~~~~~~~~
+
+In order to indicate which request has been completed, every request is
+identified by an integer, ranging from 0 to the dispatch queue size. This tag
+is generated by the block layer and later reused by the device driver, removing
+the need to create a redundant identifier. When a request is completed in the
+driver, the tag is sent back to the block layer to notify it of the finalization.
+This removes the need to do a linear search to find out which IO has been
+completed.
+
+Further reading
+---------------
+
+- `Linux Block IO: Introducing Multi-queue SSD Access on Multi-core Systems <http://kernel.dk/blk-mq.pdf>`_
+
+- `NOOP scheduler <https://en.wikipedia.org/wiki/Noop_scheduler>`_
+
+- `Null block device driver <https://www.kernel.org/doc/html/latest/block/null_blk.html>`_
+
+Source code documentation
+=========================
+
+.. kernel-doc:: include/linux/blk-mq.h
+
+.. kernel-doc:: block/blk-mq.c
diff --git a/Documentation/block/capability.rst b/Documentation/block/capability.rst
new file mode 100644
index 000000000..2ae7f0647
--- /dev/null
+++ b/Documentation/block/capability.rst
@@ -0,0 +1,10 @@
+===============================
+Generic Block Device Capability
+===============================
+
+This file documents the sysfs file ``block/<disk>/capability``.
+
+``capability`` is a bitfield, printed in hexadecimal, indicating which
+capabilities a specific block device supports:
+
+.. kernel-doc:: include/linux/blkdev.h
diff --git a/Documentation/block/cmdline-partition.rst b/Documentation/block/cmdline-partition.rst
new file mode 100644
index 000000000..530bedff5
--- /dev/null
+++ b/Documentation/block/cmdline-partition.rst
@@ -0,0 +1,53 @@
+==============================================
+Embedded device command line partition parsing
+==============================================
+
+The "blkdevparts" command line option adds support for reading the
+block device partition table from the kernel command line.
+
+It is typically used for fixed block (eMMC) embedded devices.
+It has no MBR, so saves storage space. Bootloader can be easily accessed
+by absolute address of data on the block device.
+Users can easily change the partition.
+
+The format for the command line is just like mtdparts:
+
+blkdevparts=<blkdev-def>[;<blkdev-def>]
+  <blkdev-def> := <blkdev-id>:<partdef>[,<partdef>]
+    <partdef> := <size>[@<offset>](part-name)
+
+<blkdev-id>
+    block device disk name. Embedded device uses fixed block device.
+    Its disk name is also fixed, such as: mmcblk0, mmcblk1, mmcblk0boot0.
+
+<size>
+    partition size, in bytes, such as: 512, 1m, 1G.
+    size may contain an optional suffix of (upper or lower case):
+
+      K, M, G, T, P, E.
+
+    "-" is used to denote all remaining space.
+
+<offset>
+    partition start address, in bytes.
+    offset may contain an optional suffix of (upper or lower case):
+
+      K, M, G, T, P, E.
+
+(part-name)
+    partition name. Kernel sends uevent with "PARTNAME". Application can
+    create a link to block device partition with the name "PARTNAME".
+    User space application can access partition by partition name.
+
+Example:
+
+    eMMC disk names are "mmcblk0" and "mmcblk0boot0".
+
+  bootargs::
+
+    'blkdevparts=mmcblk0:1G(data0),1G(data1),-;mmcblk0boot0:1m(boot),-(kernel)'
+
+  dmesg::
+
+    mmcblk0: p1(data0) p2(data1) p3()
+    mmcblk0boot0: p1(boot) p2(kernel)
diff --git a/Documentation/block/data-integrity.rst b/Documentation/block/data-integrity.rst
new file mode 100644
index 000000000..07a97aa26
--- /dev/null
+++ b/Documentation/block/data-integrity.rst
@@ -0,0 +1,291 @@
+==============
+Data Integrity
+==============
+
+1. Introduction
+===============
+
+Modern filesystems feature checksumming of data and metadata to
+protect against data corruption.  However, the detection of the
+corruption is done at read time which could potentially be months
+after the data was written.  At that point the original data that the
+application tried to write is most likely lost.
+
+The solution is to ensure that the disk is actually storing what the
+application meant it to.  Recent additions to both the SCSI family
+protocols (SBC Data Integrity Field, SCC protection proposal) as well
+as SATA/T13 (External Path Protection) try to remedy this by adding
+support for appending integrity metadata to an I/O.  The integrity
+metadata (or protection information in SCSI terminology) includes a
+checksum for each sector as well as an incrementing counter that
+ensures the individual sectors are written in the right order.  And
+for some protection schemes also that the I/O is written to the right
+place on disk.
+
+Current storage controllers and devices implement various protective
+measures, for instance checksumming and scrubbing.  But these
+technologies are working in their own isolated domains or at best
+between adjacent nodes in the I/O path.  The interesting thing about
+DIF and the other integrity extensions is that the protection format
+is well defined and every node in the I/O path can verify the
+integrity of the I/O and reject it if corruption is detected.  This
+allows not only corruption prevention but also isolation of the point
+of failure.
+
+2. The Data Integrity Extensions
+================================
+
+As written, the protocol extensions only protect the path between
+controller and storage device.  However, many controllers actually
+allow the operating system to interact with the integrity metadata
+(IMD).  We have been working with several FC/SAS HBA vendors to enable
+the protection information to be transferred to and from their
+controllers.
+
+The SCSI Data Integrity Field works by appending 8 bytes of protection
+information to each sector.  The data + integrity metadata is stored
+in 520 byte sectors on disk.  Data + IMD are interleaved when
+transferred between the controller and target.  The T13 proposal is
+similar.
+
+Because it is highly inconvenient for operating systems to deal with
+520 (and 4104) byte sectors, we approached several HBA vendors and
+encouraged them to allow separation of the data and integrity metadata
+scatter-gather lists.
+
+The controller will interleave the buffers on write and split them on
+read.  This means that Linux can DMA the data buffers to and from
+host memory without changes to the page cache.
+
+Also, the 16-bit CRC checksum mandated by both the SCSI and SATA specs
+is somewhat heavy to compute in software.  Benchmarks found that
+calculating this checksum had a significant impact on system
+performance for a number of workloads.  Some controllers allow a
+lighter-weight checksum to be used when interfacing with the operating
+system.  Emulex, for instance, supports the TCP/IP checksum instead.
+The IP checksum received from the OS is converted to the 16-bit CRC
+when writing and vice versa.  This allows the integrity metadata to be
+generated by Linux or the application at very low cost (comparable to
+software RAID5).
+
+The IP checksum is weaker than the CRC in terms of detecting bit
+errors.  However, the strength is really in the separation of the data
+buffers and the integrity metadata.  These two distinct buffers must
+match up for an I/O to complete.
+
+The separation of the data and integrity metadata buffers as well as
+the choice in checksums is referred to as the Data Integrity
+Extensions.  As these extensions are outside the scope of the protocol
+bodies (T10, T13), Oracle and its partners are trying to standardize
+them within the Storage Networking Industry Association.
+
+3. Kernel Changes
+=================
+
+The data integrity framework in Linux enables protection information
+to be pinned to I/Os and sent to/received from controllers that
+support it.
+
+The advantage to the integrity extensions in SCSI and SATA is that
+they enable us to protect the entire path from application to storage
+device.  However, at the same time this is also the biggest
+disadvantage. It means that the protection information must be in a
+format that can be understood by the disk.
+
+Generally Linux/POSIX applications are agnostic to the intricacies of
+the storage devices they are accessing.  The virtual filesystem switch
+and the block layer make things like hardware sector size and
+transport protocols completely transparent to the application.
+
+However, this level of detail is required when preparing the
+protection information to send to a disk.  Consequently, the very
+concept of an end-to-end protection scheme is a layering violation.
+It is completely unreasonable for an application to be aware whether
+it is accessing a SCSI or SATA disk.
+
+The data integrity support implemented in Linux attempts to hide this
+from the application.  As far as the application (and to some extent
+the kernel) is concerned, the integrity metadata is opaque information
+that's attached to the I/O.
+
+The current implementation allows the block layer to automatically
+generate the protection information for any I/O.  Eventually the
+intent is to move the integrity metadata calculation to userspace for
+user data.  Metadata and other I/O that originates within the kernel
+will still use the automatic generation interface.
+
+Some storage devices allow each hardware sector to be tagged with a
+16-bit value.  The owner of this tag space is the owner of the block
+device.  I.e. the filesystem in most cases.  The filesystem can use
+this extra space to tag sectors as they see fit.  Because the tag
+space is limited, the block interface allows tagging bigger chunks by
+way of interleaving.  This way, 8*16 bits of information can be
+attached to a typical 4KB filesystem block.
+
+This also means that applications such as fsck and mkfs will need
+access to manipulate the tags from user space.  A passthrough
+interface for this is being worked on.
+
+
+4. Block Layer Implementation Details
+=====================================
+
+4.1 Bio
+-------
+
+The data integrity patches add a new field to struct bio when
+CONFIG_BLK_DEV_INTEGRITY is enabled.  bio_integrity(bio) returns a
+pointer to a struct bip which contains the bio integrity payload.
+Essentially a bip is a trimmed down struct bio which holds a bio_vec
+containing the integrity metadata and the required housekeeping
+information (bvec pool, vector count, etc.)
+
+A kernel subsystem can enable data integrity protection on a bio by
+calling bio_integrity_alloc(bio).  This will allocate and attach the
+bip to the bio.
+
+Individual pages containing integrity metadata can subsequently be
+attached using bio_integrity_add_page().
+
+bio_free() will automatically free the bip.
+
+
+4.2 Block Device
+----------------
+
+Because the format of the protection data is tied to the physical
+disk, each block device has been extended with a block integrity
+profile (struct blk_integrity).  This optional profile is registered
+with the block layer using blk_integrity_register().
+
+The profile contains callback functions for generating and verifying
+the protection data, as well as getting and setting application tags.
+The profile also contains a few constants to aid in completing,
+merging and splitting the integrity metadata.
+
+Layered block devices will need to pick a profile that's appropriate
+for all subdevices.  blk_integrity_compare() can help with that.  DM
+and MD linear, RAID0 and RAID1 are currently supported.  RAID4/5/6
+will require extra work due to the application tag.
+
+
+5.0 Block Layer Integrity API
+=============================
+
+5.1 Normal Filesystem
+---------------------
+
+    The normal filesystem is unaware that the underlying block device
+    is capable of sending/receiving integrity metadata.  The IMD will
+    be automatically generated by the block layer at submit_bio() time
+    in case of a WRITE.  A READ request will cause the I/O integrity
+    to be verified upon completion.
+
+    IMD generation and verification can be toggled using the::
+
+      /sys/block/<bdev>/integrity/write_generate
+
+    and::
+
+      /sys/block/<bdev>/integrity/read_verify
+
+    flags.
+
+
+5.2 Integrity-Aware Filesystem
+------------------------------
+
+    A filesystem that is integrity-aware can prepare I/Os with IMD
+    attached.  It can also use the application tag space if this is
+    supported by the block device.
+
+
+    `bool bio_integrity_prep(bio);`
+
+      To generate IMD for WRITE and to set up buffers for READ, the
+      filesystem must call bio_integrity_prep(bio).
+
+      Prior to calling this function, the bio data direction and start
+      sector must be set, and the bio should have all data pages
+      added.  It is up to the caller to ensure that the bio does not
+      change while I/O is in progress.
+      Complete bio with error if prepare failed for some reson.
+
+
+5.3 Passing Existing Integrity Metadata
+---------------------------------------
+
+    Filesystems that either generate their own integrity metadata or
+    are capable of transferring IMD from user space can use the
+    following calls:
+
+
+    `struct bip * bio_integrity_alloc(bio, gfp_mask, nr_pages);`
+
+      Allocates the bio integrity payload and hangs it off of the bio.
+      nr_pages indicate how many pages of protection data need to be
+      stored in the integrity bio_vec list (similar to bio_alloc()).
+
+      The integrity payload will be freed at bio_free() time.
+
+
+    `int bio_integrity_add_page(bio, page, len, offset);`
+
+      Attaches a page containing integrity metadata to an existing
+      bio.  The bio must have an existing bip,
+      i.e. bio_integrity_alloc() must have been called.  For a WRITE,
+      the integrity metadata in the pages must be in a format
+      understood by the target device with the notable exception that
+      the sector numbers will be remapped as the request traverses the
+      I/O stack.  This implies that the pages added using this call
+      will be modified during I/O!  The first reference tag in the
+      integrity metadata must have a value of bip->bip_sector.
+
+      Pages can be added using bio_integrity_add_page() as long as
+      there is room in the bip bio_vec array (nr_pages).
+
+      Upon completion of a READ operation, the attached pages will
+      contain the integrity metadata received from the storage device.
+      It is up to the receiver to process them and verify data
+      integrity upon completion.
+
+
+5.4 Registering A Block Device As Capable Of Exchanging Integrity Metadata
+--------------------------------------------------------------------------
+
+    To enable integrity exchange on a block device the gendisk must be
+    registered as capable:
+
+    `int blk_integrity_register(gendisk, blk_integrity);`
+
+      The blk_integrity struct is a template and should contain the
+      following::
+
+        static struct blk_integrity my_profile = {
+            .name                   = "STANDARDSBODY-TYPE-VARIANT-CSUM",
+            .generate_fn            = my_generate_fn,
+	    .verify_fn              = my_verify_fn,
+	    .tuple_size             = sizeof(struct my_tuple_size),
+	    .tag_size               = <tag bytes per hw sector>,
+        };
+
+      'name' is a text string which will be visible in sysfs.  This is
+      part of the userland API so chose it carefully and never change
+      it.  The format is standards body-type-variant.
+      E.g. T10-DIF-TYPE1-IP or T13-EPP-0-CRC.
+
+      'generate_fn' generates appropriate integrity metadata (for WRITE).
+
+      'verify_fn' verifies that the data buffer matches the integrity
+      metadata.
+
+      'tuple_size' must be set to match the size of the integrity
+      metadata per sector.  I.e. 8 for DIF and EPP.
+
+      'tag_size' must be set to identify how many bytes of tag space
+      are available per hardware sector.  For DIF this is either 2 or
+      0 depending on the value of the Control Mode Page ATO bit.
+
+----------------------------------------------------------------------
+
+2007-12-24 Martin K. Petersen <martin.petersen@oracle.com>
diff --git a/Documentation/block/deadline-iosched.rst b/Documentation/block/deadline-iosched.rst
new file mode 100644
index 000000000..9f5c5a4c3
--- /dev/null
+++ b/Documentation/block/deadline-iosched.rst
@@ -0,0 +1,72 @@
+==============================
+Deadline IO scheduler tunables
+==============================
+
+This little file attempts to document how the deadline io scheduler works.
+In particular, it will clarify the meaning of the exposed tunables that may be
+of interest to power users.
+
+Selecting IO schedulers
+-----------------------
+Refer to Documentation/block/switching-sched.rst for information on
+selecting an io scheduler on a per-device basis.
+
+------------------------------------------------------------------------------
+
+read_expire	(in ms)
+-----------------------
+
+The goal of the deadline io scheduler is to attempt to guarantee a start
+service time for a request. As we focus mainly on read latencies, this is
+tunable. When a read request first enters the io scheduler, it is assigned
+a deadline that is the current time + the read_expire value in units of
+milliseconds.
+
+
+write_expire	(in ms)
+-----------------------
+
+Similar to read_expire mentioned above, but for writes.
+
+
+fifo_batch	(number of requests)
+------------------------------------
+
+Requests are grouped into ``batches`` of a particular data direction (read or
+write) which are serviced in increasing sector order.  To limit extra seeking,
+deadline expiries are only checked between batches.  fifo_batch controls the
+maximum number of requests per batch.
+
+This parameter tunes the balance between per-request latency and aggregate
+throughput.  When low latency is the primary concern, smaller is better (where
+a value of 1 yields first-come first-served behaviour).  Increasing fifo_batch
+generally improves throughput, at the cost of latency variation.
+
+
+writes_starved	(number of dispatches)
+--------------------------------------
+
+When we have to move requests from the io scheduler queue to the block
+device dispatch queue, we always give a preference to reads. However, we
+don't want to starve writes indefinitely either. So writes_starved controls
+how many times we give preference to reads over writes. When that has been
+done writes_starved number of times, we dispatch some writes based on the
+same criteria as reads.
+
+
+front_merges	(bool)
+----------------------
+
+Sometimes it happens that a request enters the io scheduler that is contiguous
+with a request that is already on the queue. Either it fits in the back of that
+request, or it fits at the front. That is called either a back merge candidate
+or a front merge candidate. Due to the way files are typically laid out,
+back merges are much more common than front merges. For some work loads, you
+may even know that it is a waste of time to spend any time attempting to
+front merge requests. Setting front_merges to 0 disables this functionality.
+Front merges may still occur due to the cached last_merge hint, but since
+that comes at basically 0 cost we leave that on. We simply disable the
+rbtree front sector lookup when the io scheduler merge function is called.
+
+
+Nov 11 2002, Jens Axboe <jens.axboe@oracle.com>
diff --git a/Documentation/block/index.rst b/Documentation/block/index.rst
new file mode 100644
index 000000000..c4c73db74
--- /dev/null
+++ b/Documentation/block/index.rst
@@ -0,0 +1,26 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=====
+Block
+=====
+
+.. toctree::
+   :maxdepth: 1
+
+   bfq-iosched
+   biovecs
+   blk-mq
+   capability
+   cmdline-partition
+   data-integrity
+   deadline-iosched
+   inline-encryption
+   ioprio
+   kyber-iosched
+   null_blk
+   pr
+   request
+   stat
+   switching-sched
+   writeback_cache_control
+   ublk
diff --git a/Documentation/block/inline-encryption.rst b/Documentation/block/inline-encryption.rst
new file mode 100644
index 000000000..f9bf18ea6
--- /dev/null
+++ b/Documentation/block/inline-encryption.rst
@@ -0,0 +1,304 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. _inline_encryption:
+
+=================
+Inline Encryption
+=================
+
+Background
+==========
+
+Inline encryption hardware sits logically between memory and disk, and can
+en/decrypt data as it goes in/out of the disk.  For each I/O request, software
+can control exactly how the inline encryption hardware will en/decrypt the data
+in terms of key, algorithm, data unit size (the granularity of en/decryption),
+and data unit number (a value that determines the initialization vector(s)).
+
+Some inline encryption hardware accepts all encryption parameters including raw
+keys directly in low-level I/O requests.  However, most inline encryption
+hardware instead has a fixed number of "keyslots" and requires that the key,
+algorithm, and data unit size first be programmed into a keyslot.  Each
+low-level I/O request then just contains a keyslot index and data unit number.
+
+Note that inline encryption hardware is very different from traditional crypto
+accelerators, which are supported through the kernel crypto API.  Traditional
+crypto accelerators operate on memory regions, whereas inline encryption
+hardware operates on I/O requests.  Thus, inline encryption hardware needs to be
+managed by the block layer, not the kernel crypto API.
+
+Inline encryption hardware is also very different from "self-encrypting drives",
+such as those based on the TCG Opal or ATA Security standards.  Self-encrypting
+drives don't provide fine-grained control of encryption and provide no way to
+verify the correctness of the resulting ciphertext.  Inline encryption hardware
+provides fine-grained control of encryption, including the choice of key and
+initialization vector for each sector, and can be tested for correctness.
+
+Objective
+=========
+
+We want to support inline encryption in the kernel.  To make testing easier, we
+also want support for falling back to the kernel crypto API when actual inline
+encryption hardware is absent.  We also want inline encryption to work with
+layered devices like device-mapper and loopback (i.e. we want to be able to use
+the inline encryption hardware of the underlying devices if present, or else
+fall back to crypto API en/decryption).
+
+Constraints and notes
+=====================
+
+- We need a way for upper layers (e.g. filesystems) to specify an encryption
+  context to use for en/decrypting a bio, and device drivers (e.g. UFSHCD) need
+  to be able to use that encryption context when they process the request.
+  Encryption contexts also introduce constraints on bio merging; the block layer
+  needs to be aware of these constraints.
+
+- Different inline encryption hardware has different supported algorithms,
+  supported data unit sizes, maximum data unit numbers, etc.  We call these
+  properties the "crypto capabilities".  We need a way for device drivers to
+  advertise crypto capabilities to upper layers in a generic way.
+
+- Inline encryption hardware usually (but not always) requires that keys be
+  programmed into keyslots before being used.  Since programming keyslots may be
+  slow and there may not be very many keyslots, we shouldn't just program the
+  key for every I/O request, but rather keep track of which keys are in the
+  keyslots and reuse an already-programmed keyslot when possible.
+
+- Upper layers typically define a specific end-of-life for crypto keys, e.g.
+  when an encrypted directory is locked or when a crypto mapping is torn down.
+  At these times, keys are wiped from memory.  We must provide a way for upper
+  layers to also evict keys from any keyslots they are present in.
+
+- When possible, device-mapper devices must be able to pass through the inline
+  encryption support of their underlying devices.  However, it doesn't make
+  sense for device-mapper devices to have keyslots themselves.
+
+Basic design
+============
+
+We introduce ``struct blk_crypto_key`` to represent an inline encryption key and
+how it will be used.  This includes the actual bytes of the key; the size of the
+key; the algorithm and data unit size the key will be used with; and the number
+of bytes needed to represent the maximum data unit number the key will be used
+with.
+
+We introduce ``struct bio_crypt_ctx`` to represent an encryption context.  It
+contains a data unit number and a pointer to a blk_crypto_key.  We add pointers
+to a bio_crypt_ctx to ``struct bio`` and ``struct request``; this allows users
+of the block layer (e.g. filesystems) to provide an encryption context when
+creating a bio and have it be passed down the stack for processing by the block
+layer and device drivers.  Note that the encryption context doesn't explicitly
+say whether to encrypt or decrypt, as that is implicit from the direction of the
+bio; WRITE means encrypt, and READ means decrypt.
+
+We also introduce ``struct blk_crypto_profile`` to contain all generic inline
+encryption-related state for a particular inline encryption device.  The
+blk_crypto_profile serves as the way that drivers for inline encryption hardware
+advertise their crypto capabilities and provide certain functions (e.g.,
+functions to program and evict keys) to upper layers.  Each device driver that
+wants to support inline encryption will construct a blk_crypto_profile, then
+associate it with the disk's request_queue.
+
+The blk_crypto_profile also manages the hardware's keyslots, when applicable.
+This happens in the block layer, so that users of the block layer can just
+specify encryption contexts and don't need to know about keyslots at all, nor do
+device drivers need to care about most details of keyslot management.
+
+Specifically, for each keyslot, the block layer (via the blk_crypto_profile)
+keeps track of which blk_crypto_key that keyslot contains (if any), and how many
+in-flight I/O requests are using it.  When the block layer creates a
+``struct request`` for a bio that has an encryption context, it grabs a keyslot
+that already contains the key if possible.  Otherwise it waits for an idle
+keyslot (a keyslot that isn't in-use by any I/O), then programs the key into the
+least-recently-used idle keyslot using the function the device driver provided.
+In both cases, the resulting keyslot is stored in the ``crypt_keyslot`` field of
+the request, where it is then accessible to device drivers and is released after
+the request completes.
+
+``struct request`` also contains a pointer to the original bio_crypt_ctx.
+Requests can be built from multiple bios, and the block layer must take the
+encryption context into account when trying to merge bios and requests.  For two
+bios/requests to be merged, they must have compatible encryption contexts: both
+unencrypted, or both encrypted with the same key and contiguous data unit
+numbers.  Only the encryption context for the first bio in a request is
+retained, since the remaining bios have been verified to be merge-compatible
+with the first bio.
+
+To make it possible for inline encryption to work with request_queue based
+layered devices, when a request is cloned, its encryption context is cloned as
+well.  When the cloned request is submitted, it is then processed as usual; this
+includes getting a keyslot from the clone's target device if needed.
+
+blk-crypto-fallback
+===================
+
+It is desirable for the inline encryption support of upper layers (e.g.
+filesystems) to be testable without real inline encryption hardware, and
+likewise for the block layer's keyslot management logic.  It is also desirable
+to allow upper layers to just always use inline encryption rather than have to
+implement encryption in multiple ways.
+
+Therefore, we also introduce *blk-crypto-fallback*, which is an implementation
+of inline encryption using the kernel crypto API.  blk-crypto-fallback is built
+into the block layer, so it works on any block device without any special setup.
+Essentially, when a bio with an encryption context is submitted to a
+block_device that doesn't support that encryption context, the block layer will
+handle en/decryption of the bio using blk-crypto-fallback.
+
+For encryption, the data cannot be encrypted in-place, as callers usually rely
+on it being unmodified.  Instead, blk-crypto-fallback allocates bounce pages,
+fills a new bio with those bounce pages, encrypts the data into those bounce
+pages, and submits that "bounce" bio.  When the bounce bio completes,
+blk-crypto-fallback completes the original bio.  If the original bio is too
+large, multiple bounce bios may be required; see the code for details.
+
+For decryption, blk-crypto-fallback "wraps" the bio's completion callback
+(``bi_complete``) and private data (``bi_private``) with its own, unsets the
+bio's encryption context, then submits the bio.  If the read completes
+successfully, blk-crypto-fallback restores the bio's original completion
+callback and private data, then decrypts the bio's data in-place using the
+kernel crypto API.  Decryption happens from a workqueue, as it may sleep.
+Afterwards, blk-crypto-fallback completes the bio.
+
+In both cases, the bios that blk-crypto-fallback submits no longer have an
+encryption context.  Therefore, lower layers only see standard unencrypted I/O.
+
+blk-crypto-fallback also defines its own blk_crypto_profile and has its own
+"keyslots"; its keyslots contain ``struct crypto_skcipher`` objects.  The reason
+for this is twofold.  First, it allows the keyslot management logic to be tested
+without actual inline encryption hardware.  Second, similar to actual inline
+encryption hardware, the crypto API doesn't accept keys directly in requests but
+rather requires that keys be set ahead of time, and setting keys can be
+expensive; moreover, allocating a crypto_skcipher can't happen on the I/O path
+at all due to the locks it takes.  Therefore, the concept of keyslots still
+makes sense for blk-crypto-fallback.
+
+Note that regardless of whether real inline encryption hardware or
+blk-crypto-fallback is used, the ciphertext written to disk (and hence the
+on-disk format of data) will be the same (assuming that both the inline
+encryption hardware's implementation and the kernel crypto API's implementation
+of the algorithm being used adhere to spec and function correctly).
+
+blk-crypto-fallback is optional and is controlled by the
+``CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK`` kernel configuration option.
+
+API presented to users of the block layer
+=========================================
+
+``blk_crypto_config_supported()`` allows users to check ahead of time whether
+inline encryption with particular crypto settings will work on a particular
+block_device -- either via hardware or via blk-crypto-fallback.  This function
+takes in a ``struct blk_crypto_config`` which is like blk_crypto_key, but omits
+the actual bytes of the key and instead just contains the algorithm, data unit
+size, etc.  This function can be useful if blk-crypto-fallback is disabled.
+
+``blk_crypto_init_key()`` allows users to initialize a blk_crypto_key.
+
+Users must call ``blk_crypto_start_using_key()`` before actually starting to use
+a blk_crypto_key on a block_device (even if ``blk_crypto_config_supported()``
+was called earlier).  This is needed to initialize blk-crypto-fallback if it
+will be needed.  This must not be called from the data path, as this may have to
+allocate resources, which may deadlock in that case.
+
+Next, to attach an encryption context to a bio, users should call
+``bio_crypt_set_ctx()``.  This function allocates a bio_crypt_ctx and attaches
+it to a bio, given the blk_crypto_key and the data unit number that will be used
+for en/decryption.  Users don't need to worry about freeing the bio_crypt_ctx
+later, as that happens automatically when the bio is freed or reset.
+
+Finally, when done using inline encryption with a blk_crypto_key on a
+block_device, users must call ``blk_crypto_evict_key()``.  This ensures that
+the key is evicted from all keyslots it may be programmed into and unlinked from
+any kernel data structures it may be linked into.
+
+In summary, for users of the block layer, the lifecycle of a blk_crypto_key is
+as follows:
+
+1. ``blk_crypto_config_supported()`` (optional)
+2. ``blk_crypto_init_key()``
+3. ``blk_crypto_start_using_key()``
+4. ``bio_crypt_set_ctx()`` (potentially many times)
+5. ``blk_crypto_evict_key()`` (after all I/O has completed)
+6. Zeroize the blk_crypto_key (this has no dedicated function)
+
+If a blk_crypto_key is being used on multiple block_devices, then
+``blk_crypto_config_supported()`` (if used), ``blk_crypto_start_using_key()``,
+and ``blk_crypto_evict_key()`` must be called on each block_device.
+
+API presented to device drivers
+===============================
+
+A device driver that wants to support inline encryption must set up a
+blk_crypto_profile in the request_queue of its device.  To do this, it first
+must call ``blk_crypto_profile_init()`` (or its resource-managed variant
+``devm_blk_crypto_profile_init()``), providing the number of keyslots.
+
+Next, it must advertise its crypto capabilities by setting fields in the
+blk_crypto_profile, e.g. ``modes_supported`` and ``max_dun_bytes_supported``.
+
+It then must set function pointers in the ``ll_ops`` field of the
+blk_crypto_profile to tell upper layers how to control the inline encryption
+hardware, e.g. how to program and evict keyslots.  Most drivers will need to
+implement ``keyslot_program`` and ``keyslot_evict``.  For details, see the
+comments for ``struct blk_crypto_ll_ops``.
+
+Once the driver registers a blk_crypto_profile with a request_queue, I/O
+requests the driver receives via that queue may have an encryption context.  All
+encryption contexts will be compatible with the crypto capabilities declared in
+the blk_crypto_profile, so drivers don't need to worry about handling
+unsupported requests.  Also, if a nonzero number of keyslots was declared in the
+blk_crypto_profile, then all I/O requests that have an encryption context will
+also have a keyslot which was already programmed with the appropriate key.
+
+If the driver implements runtime suspend and its blk_crypto_ll_ops don't work
+while the device is runtime-suspended, then the driver must also set the ``dev``
+field of the blk_crypto_profile to point to the ``struct device`` that will be
+resumed before any of the low-level operations are called.
+
+If there are situations where the inline encryption hardware loses the contents
+of its keyslots, e.g. device resets, the driver must handle reprogramming the
+keyslots.  To do this, the driver may call ``blk_crypto_reprogram_all_keys()``.
+
+Finally, if the driver used ``blk_crypto_profile_init()`` instead of
+``devm_blk_crypto_profile_init()``, then it is responsible for calling
+``blk_crypto_profile_destroy()`` when the crypto profile is no longer needed.
+
+Layered Devices
+===============
+
+Request queue based layered devices like dm-rq that wish to support inline
+encryption need to create their own blk_crypto_profile for their request_queue,
+and expose whatever functionality they choose. When a layered device wants to
+pass a clone of that request to another request_queue, blk-crypto will
+initialize and prepare the clone as necessary; see
+``blk_crypto_insert_cloned_request()``.
+
+Interaction between inline encryption and blk integrity
+=======================================================
+
+At the time of this patch, there is no real hardware that supports both these
+features. However, these features do interact with each other, and it's not
+completely trivial to make them both work together properly. In particular,
+when a WRITE bio wants to use inline encryption on a device that supports both
+features, the bio will have an encryption context specified, after which
+its integrity information is calculated (using the plaintext data, since
+the encryption will happen while data is being written), and the data and
+integrity info is sent to the device. Obviously, the integrity info must be
+verified before the data is encrypted. After the data is encrypted, the device
+must not store the integrity info that it received with the plaintext data
+since that might reveal information about the plaintext data. As such, it must
+re-generate the integrity info from the ciphertext data and store that on disk
+instead. Another issue with storing the integrity info of the plaintext data is
+that it changes the on disk format depending on whether hardware inline
+encryption support is present or the kernel crypto API fallback is used (since
+if the fallback is used, the device will receive the integrity info of the
+ciphertext, not that of the plaintext).
+
+Because there isn't any real hardware yet, it seems prudent to assume that
+hardware implementations might not implement both features together correctly,
+and disallow the combination for now. Whenever a device supports integrity, the
+kernel will pretend that the device does not support hardware inline encryption
+(by setting the blk_crypto_profile in the request_queue of the device to NULL).
+When the crypto API fallback is enabled, this means that all bios with and
+encryption context will use the fallback, and IO will complete as usual.  When
+the fallback is disabled, a bio with an encryption context will be failed.
diff --git a/Documentation/block/ioprio.rst b/Documentation/block/ioprio.rst
new file mode 100644
index 000000000..f72b0de65
--- /dev/null
+++ b/Documentation/block/ioprio.rst
@@ -0,0 +1,182 @@
+===================
+Block io priorities
+===================
+
+
+Intro
+-----
+
+With the introduction of cfq v3 (aka cfq-ts or time sliced cfq), basic io
+priorities are supported for reads on files.  This enables users to io nice
+processes or process groups, similar to what has been possible with cpu
+scheduling for ages.  This document mainly details the current possibilities
+with cfq; other io schedulers do not support io priorities thus far.
+
+Scheduling classes
+------------------
+
+CFQ implements three generic scheduling classes that determine how io is
+served for a process.
+
+IOPRIO_CLASS_RT: This is the realtime io class. This scheduling class is given
+higher priority than any other in the system, processes from this class are
+given first access to the disk every time. Thus it needs to be used with some
+care, one io RT process can starve the entire system. Within the RT class,
+there are 8 levels of class data that determine exactly how much time this
+process needs the disk for on each service. In the future this might change
+to be more directly mappable to performance, by passing in a wanted data
+rate instead.
+
+IOPRIO_CLASS_BE: This is the best-effort scheduling class, which is the default
+for any process that hasn't set a specific io priority. The class data
+determines how much io bandwidth the process will get, it's directly mappable
+to the cpu nice levels just more coarsely implemented. 0 is the highest
+BE prio level, 7 is the lowest. The mapping between cpu nice level and io
+nice level is determined as: io_nice = (cpu_nice + 20) / 5.
+
+IOPRIO_CLASS_IDLE: This is the idle scheduling class, processes running at this
+level only get io time when no one else needs the disk. The idle class has no
+class data, since it doesn't really apply here.
+
+Tools
+-----
+
+See below for a sample ionice tool. Usage::
+
+	# ionice -c<class> -n<level> -p<pid>
+
+If pid isn't given, the current process is assumed. IO priority settings
+are inherited on fork, so you can use ionice to start the process at a given
+level::
+
+	# ionice -c2 -n0 /bin/ls
+
+will run ls at the best-effort scheduling class at the highest priority.
+For a running process, you can give the pid instead::
+
+	# ionice -c1 -n2 -p100
+
+will change pid 100 to run at the realtime scheduling class, at priority 2.
+
+ionice.c tool::
+
+  #include <stdio.h>
+  #include <stdlib.h>
+  #include <errno.h>
+  #include <getopt.h>
+  #include <unistd.h>
+  #include <sys/ptrace.h>
+  #include <asm/unistd.h>
+
+  extern int sys_ioprio_set(int, int, int);
+  extern int sys_ioprio_get(int, int);
+
+  #if defined(__i386__)
+  #define __NR_ioprio_set		289
+  #define __NR_ioprio_get		290
+  #elif defined(__ppc__)
+  #define __NR_ioprio_set		273
+  #define __NR_ioprio_get		274
+  #elif defined(__x86_64__)
+  #define __NR_ioprio_set		251
+  #define __NR_ioprio_get		252
+  #elif defined(__ia64__)
+  #define __NR_ioprio_set		1274
+  #define __NR_ioprio_get		1275
+  #else
+  #error "Unsupported arch"
+  #endif
+
+  static inline int ioprio_set(int which, int who, int ioprio)
+  {
+	return syscall(__NR_ioprio_set, which, who, ioprio);
+  }
+
+  static inline int ioprio_get(int which, int who)
+  {
+	return syscall(__NR_ioprio_get, which, who);
+  }
+
+  enum {
+	IOPRIO_CLASS_NONE,
+	IOPRIO_CLASS_RT,
+	IOPRIO_CLASS_BE,
+	IOPRIO_CLASS_IDLE,
+  };
+
+  enum {
+	IOPRIO_WHO_PROCESS = 1,
+	IOPRIO_WHO_PGRP,
+	IOPRIO_WHO_USER,
+  };
+
+  #define IOPRIO_CLASS_SHIFT	13
+
+  const char *to_prio[] = { "none", "realtime", "best-effort", "idle", };
+
+  int main(int argc, char *argv[])
+  {
+	int ioprio = 4, set = 0, ioprio_class = IOPRIO_CLASS_BE;
+	int c, pid = 0;
+
+	while ((c = getopt(argc, argv, "+n:c:p:")) != EOF) {
+		switch (c) {
+		case 'n':
+			ioprio = strtol(optarg, NULL, 10);
+			set = 1;
+			break;
+		case 'c':
+			ioprio_class = strtol(optarg, NULL, 10);
+			set = 1;
+			break;
+		case 'p':
+			pid = strtol(optarg, NULL, 10);
+			break;
+		}
+	}
+
+	switch (ioprio_class) {
+		case IOPRIO_CLASS_NONE:
+			ioprio_class = IOPRIO_CLASS_BE;
+			break;
+		case IOPRIO_CLASS_RT:
+		case IOPRIO_CLASS_BE:
+			break;
+		case IOPRIO_CLASS_IDLE:
+			ioprio = 7;
+			break;
+		default:
+			printf("bad prio class %d\n", ioprio_class);
+			return 1;
+	}
+
+	if (!set) {
+		if (!pid && argv[optind])
+			pid = strtol(argv[optind], NULL, 10);
+
+		ioprio = ioprio_get(IOPRIO_WHO_PROCESS, pid);
+
+		printf("pid=%d, %d\n", pid, ioprio);
+
+		if (ioprio == -1)
+			perror("ioprio_get");
+		else {
+			ioprio_class = ioprio >> IOPRIO_CLASS_SHIFT;
+			ioprio = ioprio & 0xff;
+			printf("%s: prio %d\n", to_prio[ioprio_class], ioprio);
+		}
+	} else {
+		if (ioprio_set(IOPRIO_WHO_PROCESS, pid, ioprio | ioprio_class << IOPRIO_CLASS_SHIFT) == -1) {
+			perror("ioprio_set");
+			return 1;
+		}
+
+		if (argv[optind])
+			execvp(argv[optind], &argv[optind]);
+	}
+
+	return 0;
+  }
+
+
+March 11 2005, Jens Axboe <jens.axboe@oracle.com>
diff --git a/Documentation/block/kyber-iosched.rst b/Documentation/block/kyber-iosched.rst
new file mode 100644
index 000000000..3e164dd06
--- /dev/null
+++ b/Documentation/block/kyber-iosched.rst
@@ -0,0 +1,15 @@
+============================
+Kyber I/O scheduler tunables
+============================
+
+The only two tunables for the Kyber scheduler are the target latencies for
+reads and synchronous writes. Kyber will throttle requests in order to meet
+these target latencies.
+
+read_lat_nsec
+-------------
+Target latency for reads (in nanoseconds).
+
+write_lat_nsec
+--------------
+Target latency for synchronous writes (in nanoseconds).
diff --git a/Documentation/block/null_blk.rst b/Documentation/block/null_blk.rst
new file mode 100644
index 000000000..4dd78f24d
--- /dev/null
+++ b/Documentation/block/null_blk.rst
@@ -0,0 +1,151 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+========================
+Null block device driver
+========================
+
+Overview
+========
+
+The null block device (``/dev/nullb*``) is used for benchmarking the various
+block-layer implementations. It emulates a block device of X gigabytes in size.
+It does not execute any read/write operation, just mark them as complete in
+the request queue. The following instances are possible:
+
+  Multi-queue block-layer
+
+    - Request-based.
+    - Configurable submission queues per device.
+
+  No block-layer (Known as bio-based)
+
+    - Bio-based. IO requests are submitted directly to the device driver.
+    - Directly accepts bio data structure and returns them.
+
+All of them have a completion queue for each core in the system.
+
+Module parameters
+=================
+
+queue_mode=[0-2]: Default: 2-Multi-queue
+  Selects which block-layer the module should instantiate with.
+
+  =  ============
+  0  Bio-based
+  1  Single-queue (deprecated)
+  2  Multi-queue
+  =  ============
+
+home_node=[0--nr_nodes]: Default: NUMA_NO_NODE
+  Selects what CPU node the data structures are allocated from.
+
+gb=[Size in GB]: Default: 250GB
+  The size of the device reported to the system.
+
+bs=[Block size (in bytes)]: Default: 512 bytes
+  The block size reported to the system.
+
+nr_devices=[Number of devices]: Default: 1
+  Number of block devices instantiated. They are instantiated as /dev/nullb0,
+  etc.
+
+irqmode=[0-2]: Default: 1-Soft-irq
+  The completion mode used for completing IOs to the block-layer.
+
+  =  ===========================================================================
+  0  None.
+  1  Soft-irq. Uses IPI to complete IOs across CPU nodes. Simulates the overhead
+     when IOs are issued from another CPU node than the home the device is
+     connected to.
+  2  Timer: Waits a specific period (completion_nsec) for each IO before
+     completion.
+  =  ===========================================================================
+
+completion_nsec=[ns]: Default: 10,000ns
+  Combined with irqmode=2 (timer). The time each completion event must wait.
+
+submit_queues=[1..nr_cpus]: Default: 1
+  The number of submission queues attached to the device driver. If unset, it
+  defaults to 1. For multi-queue, it is ignored when use_per_node_hctx module
+  parameter is 1.
+
+hw_queue_depth=[0..qdepth]: Default: 64
+  The hardware queue depth of the device.
+
+memory_backed=[0/1]: Default: 0
+  Whether or not to use a memory buffer to respond to IO requests
+
+  =  =============================================
+  0  Transfer no data in response to IO requests
+  1  Use a memory buffer to respond to IO requests
+  =  =============================================
+
+discard=[0/1]: Default: 0
+  Support discard operations (requires memory-backed null_blk device).
+
+  =  =====================================
+  0  Do not support discard operations
+  1  Enable support for discard operations
+  =  =====================================
+
+cache_size=[Size in MB]: Default: 0
+  Cache size in MB for memory-backed device.
+
+mbps=[Maximum bandwidth in MB/s]: Default: 0 (no limit)
+  Bandwidth limit for device performance.
+
+Multi-queue specific parameters
+-------------------------------
+
+use_per_node_hctx=[0/1]: Default: 0
+  Number of hardware context queues.
+
+  =  =====================================================================
+  0  The number of submit queues are set to the value of the submit_queues
+     parameter.
+  1  The multi-queue block layer is instantiated with a hardware dispatch
+     queue for each CPU node in the system.
+  =  =====================================================================
+
+no_sched=[0/1]: Default: 0
+  Enable/disable the io scheduler.
+
+  =  ======================================
+  0  nullb* use default blk-mq io scheduler
+  1  nullb* doesn't use io scheduler
+  =  ======================================
+
+blocking=[0/1]: Default: 0
+  Blocking behavior of the request queue.
+
+  =  ===============================================================
+  0  Register as a non-blocking blk-mq driver device.
+  1  Register as a blocking blk-mq driver device, null_blk will set
+     the BLK_MQ_F_BLOCKING flag, indicating that it sometimes/always
+     needs to block in its ->queue_rq() function.
+  =  ===============================================================
+
+shared_tags=[0/1]: Default: 0
+  Sharing tags between devices.
+
+  =  ================================================================
+  0  Tag set is not shared.
+  1  Tag set shared between devices for blk-mq. Only makes sense with
+     nr_devices > 1, otherwise there's no tag set to share.
+  =  ================================================================
+
+zoned=[0/1]: Default: 0
+  Device is a random-access or a zoned block device.
+
+  =  ======================================================================
+  0  Block device is exposed as a random-access block device.
+  1  Block device is exposed as a host-managed zoned block device. Requires
+     CONFIG_BLK_DEV_ZONED.
+  =  ======================================================================
+
+zone_size=[MB]: Default: 256
+  Per zone size when exposed as a zoned block device. Must be a power of two.
+
+zone_nr_conv=[nr_conv]: Default: 0
+  The number of conventional zones to create when block device is zoned.  If
+  zone_nr_conv >= nr_zones, it will be reduced to nr_zones - 1.
diff --git a/Documentation/block/pr.rst b/Documentation/block/pr.rst
new file mode 100644
index 000000000..c893d6da8
--- /dev/null
+++ b/Documentation/block/pr.rst
@@ -0,0 +1,119 @@
+===============================================
+Block layer support for Persistent Reservations
+===============================================
+
+The Linux kernel supports a user space interface for simplified
+Persistent Reservations which map to block devices that support
+these (like SCSI). Persistent Reservations allow restricting
+access to block devices to specific initiators in a shared storage
+setup.
+
+This document gives a general overview of the support ioctl commands.
+For a more detailed reference please refer to the SCSI Primary
+Commands standard, specifically the section on Reservations and the
+"PERSISTENT RESERVE IN" and "PERSISTENT RESERVE OUT" commands.
+
+All implementations are expected to ensure the reservations survive
+a power loss and cover all connections in a multi path environment.
+These behaviors are optional in SPC but will be automatically applied
+by Linux.
+
+
+The following types of reservations are supported:
+--------------------------------------------------
+
+ - PR_WRITE_EXCLUSIVE
+	Only the initiator that owns the reservation can write to the
+	device.  Any initiator can read from the device.
+
+ - PR_EXCLUSIVE_ACCESS
+	Only the initiator that owns the reservation can access the
+	device.
+
+ - PR_WRITE_EXCLUSIVE_REG_ONLY
+	Only initiators with a registered key can write to the device,
+	Any initiator can read from the device.
+
+ - PR_EXCLUSIVE_ACCESS_REG_ONLY
+	Only initiators with a registered key can access the device.
+
+ - PR_WRITE_EXCLUSIVE_ALL_REGS
+
+	Only initiators with a registered key can write to the device,
+	Any initiator can read from the device.
+	All initiators with a registered key are considered reservation
+	holders.
+	Please reference the SPC spec on the meaning of a reservation
+	holder if you want to use this type.
+
+ - PR_EXCLUSIVE_ACCESS_ALL_REGS
+	Only initiators with a registered key can access the device.
+	All initiators with a registered key are considered reservation
+	holders.
+	Please reference the SPC spec on the meaning of a reservation
+	holder if you want to use this type.
+
+
+The following ioctl are supported:
+----------------------------------
+
+1. IOC_PR_REGISTER
+^^^^^^^^^^^^^^^^^^
+
+This ioctl command registers a new reservation if the new_key argument
+is non-null.  If no existing reservation exists old_key must be zero,
+if an existing reservation should be replaced old_key must contain
+the old reservation key.
+
+If the new_key argument is 0 it unregisters the existing reservation passed
+in old_key.
+
+
+2. IOC_PR_RESERVE
+^^^^^^^^^^^^^^^^^
+
+This ioctl command reserves the device and thus restricts access for other
+devices based on the type argument.  The key argument must be the existing
+reservation key for the device as acquired by the IOC_PR_REGISTER,
+IOC_PR_REGISTER_IGNORE, IOC_PR_PREEMPT or IOC_PR_PREEMPT_ABORT commands.
+
+
+3. IOC_PR_RELEASE
+^^^^^^^^^^^^^^^^^
+
+This ioctl command releases the reservation specified by key and flags
+and thus removes any access restriction implied by it.
+
+
+4. IOC_PR_PREEMPT
+^^^^^^^^^^^^^^^^^
+
+This ioctl command releases the existing reservation referred to by
+old_key and replaces it with a new reservation of type for the
+reservation key new_key.
+
+
+5. IOC_PR_PREEMPT_ABORT
+^^^^^^^^^^^^^^^^^^^^^^^
+
+This ioctl command works like IOC_PR_PREEMPT except that it also aborts
+any outstanding command sent over a connection identified by old_key.
+
+6. IOC_PR_CLEAR
+^^^^^^^^^^^^^^^
+
+This ioctl command unregisters both key and any other reservation key
+registered with the device and drops any existing reservation.
+
+
+Flags
+-----
+
+All the ioctls have a flag field.  Currently only one flag is supported:
+
+ - PR_FL_IGNORE_KEY
+	Ignore the existing reservation key.  This is commonly supported for
+	IOC_PR_REGISTER, and some implementation may support the flag for
+	IOC_PR_RESERVE.
+
+For all unknown flags the kernel will return -EOPNOTSUPP.
diff --git a/Documentation/block/request.rst b/Documentation/block/request.rst
new file mode 100644
index 000000000..747021e1f
--- /dev/null
+++ b/Documentation/block/request.rst
@@ -0,0 +1,99 @@
+============================
+struct request documentation
+============================
+
+Jens Axboe <jens.axboe@oracle.com> 27/05/02
+
+
+.. FIXME:
+   No idea about what does mean - seems just some noise, so comment it
+
+   1.0
+   Index
+
+   2.0 Struct request members classification
+
+       2.1 struct request members explanation
+
+   3.0
+
+
+   2.0
+
+
+
+Short explanation of request members
+====================================
+
+Classification flags:
+
+	=	====================
+	D	driver member
+	B	block layer member
+	I	I/O scheduler member
+	=	====================
+
+Unless an entry contains a D classification, a device driver must not access
+this member. Some members may contain D classifications, but should only be
+access through certain macros or functions (eg ->flags).
+
+<linux/blkdev.h>
+
+=============================== ======= =======================================
+Member				Flag	Comment
+=============================== ======= =======================================
+struct list_head queuelist	BI	Organization on various internal
+					queues
+
+``void *elevator_private``	I	I/O scheduler private data
+
+unsigned char cmd[16]		D	Driver can use this for setting up
+					a cdb before execution, see
+					blk_queue_prep_rq
+
+unsigned long flags		DBI	Contains info about data direction,
+					request type, etc.
+
+int rq_status			D	Request status bits
+
+kdev_t rq_dev			DBI	Target device
+
+int errors			DB	Error counts
+
+sector_t sector			DBI	Target location
+
+unsigned long hard_nr_sectors	B	Used to keep sector sane
+
+unsigned long nr_sectors	DBI	Total number of sectors in request
+
+unsigned long hard_nr_sectors	B	Used to keep nr_sectors sane
+
+unsigned short nr_phys_segments	DB	Number of physical scatter gather
+					segments in a request
+
+unsigned short nr_hw_segments	DB	Number of hardware scatter gather
+					segments in a request
+
+unsigned int current_nr_sectors	DB	Number of sectors in first segment
+					of request
+
+unsigned int hard_cur_sectors	B	Used to keep current_nr_sectors sane
+
+int tag				DB	TCQ tag, if assigned
+
+``void *special``		D	Free to be used by driver
+
+``char *buffer``		D	Map of first segment, also see
+					section on bouncing SECTION
+
+``struct completion *waiting``	D	Can be used by driver to get signalled
+					on request completion
+
+``struct bio *bio``		DBI	First bio in request
+
+``struct bio *biotail``		DBI	Last bio in request
+
+``struct request_queue *q``	DB	Request queue this request belongs to
+
+``struct request_list *rl``	B	Request list this request came from
+=============================== ======= =======================================
diff --git a/Documentation/block/stat.rst b/Documentation/block/stat.rst
new file mode 100644
index 000000000..a1cd9db20
--- /dev/null
+++ b/Documentation/block/stat.rst
@@ -0,0 +1,103 @@
+===============================================
+Block layer statistics in /sys/block/<dev>/stat
+===============================================
+
+This file documents the contents of the /sys/block/<dev>/stat file.
+
+The stat file provides several statistics about the state of block
+device <dev>.
+
+Q.
+   Why are there multiple statistics in a single file?  Doesn't sysfs
+   normally contain a single value per file?
+
+A.
+   By having a single file, the kernel can guarantee that the statistics
+   represent a consistent snapshot of the state of the device.  If the
+   statistics were exported as multiple files containing one statistic
+   each, it would be impossible to guarantee that a set of readings
+   represent a single point in time.
+
+The stat file consists of a single line of text containing 17 decimal
+values separated by whitespace.  The fields are summarized in the
+following table, and described in more detail below.
+
+
+=============== ============= =================================================
+Name            units         description
+=============== ============= =================================================
+read I/Os       requests      number of read I/Os processed
+read merges     requests      number of read I/Os merged with in-queue I/O
+read sectors    sectors       number of sectors read
+read ticks      milliseconds  total wait time for read requests
+write I/Os      requests      number of write I/Os processed
+write merges    requests      number of write I/Os merged with in-queue I/O
+write sectors   sectors       number of sectors written
+write ticks     milliseconds  total wait time for write requests
+in_flight       requests      number of I/Os currently in flight
+io_ticks        milliseconds  total time this block device has been active
+time_in_queue   milliseconds  total wait time for all requests
+discard I/Os    requests      number of discard I/Os processed
+discard merges  requests      number of discard I/Os merged with in-queue I/O
+discard sectors sectors       number of sectors discarded
+discard ticks   milliseconds  total wait time for discard requests
+flush I/Os      requests      number of flush I/Os processed
+flush ticks     milliseconds  total wait time for flush requests
+=============== ============= =================================================
+
+read I/Os, write I/Os, discard I/0s
+===================================
+
+These values increment when an I/O request completes.
+
+flush I/Os
+==========
+
+These values increment when an flush I/O request completes.
+
+Block layer combines flush requests and executes at most one at a time.
+This counts flush requests executed by disk. Not tracked for partitions.
+
+read merges, write merges, discard merges
+=========================================
+
+These values increment when an I/O request is merged with an
+already-queued I/O request.
+
+read sectors, write sectors, discard_sectors
+============================================
+
+These values count the number of sectors read from, written to, or
+discarded from this block device.  The "sectors" in question are the
+standard UNIX 512-byte sectors, not any device- or filesystem-specific
+block size.  The counters are incremented when the I/O completes.
+
+read ticks, write ticks, discard ticks, flush ticks
+===================================================
+
+These values count the number of milliseconds that I/O requests have
+waited on this block device.  If there are multiple I/O requests waiting,
+these values will increase at a rate greater than 1000/second; for
+example, if 60 read requests wait for an average of 30 ms, the read_ticks
+field will increase by 60*30 = 1800.
+
+in_flight
+=========
+
+This value counts the number of I/O requests that have been issued to
+the device driver but have not yet completed.  It does not include I/O
+requests that are in the queue but not yet issued to the device driver.
+
+io_ticks
+========
+
+This value counts the number of milliseconds during which the device has
+had I/O requests queued.
+
+time_in_queue
+=============
+
+This value counts the number of milliseconds that I/O requests have waited
+on this block device.  If there are multiple I/O requests waiting, this
+value will increase as the product of the number of milliseconds times the
+number of requests waiting (see "read ticks" above for an example).
diff --git a/Documentation/block/switching-sched.rst b/Documentation/block/switching-sched.rst
new file mode 100644
index 000000000..520f6b857
--- /dev/null
+++ b/Documentation/block/switching-sched.rst
@@ -0,0 +1,35 @@
+===================
+Switching Scheduler
+===================
+
+Each io queue has a set of io scheduler tunables associated with it. These
+tunables control how the io scheduler works. You can find these entries
+in::
+
+	/sys/block/<device>/queue/iosched
+
+assuming that you have sysfs mounted on /sys. If you don't have sysfs mounted,
+you can do so by typing::
+
+	# mount none /sys -t sysfs
+
+It is possible to change the IO scheduler for a given block device on
+the fly to select one of mq-deadline, none, bfq, or kyber schedulers -
+which can improve that device's throughput.
+
+To set a specific scheduler, simply do this::
+
+	echo SCHEDNAME > /sys/block/DEV/queue/scheduler
+
+where SCHEDNAME is the name of a defined IO scheduler, and DEV is the
+device name (hda, hdb, sga, or whatever you happen to have).
+
+The list of defined schedulers can be found by simply doing
+a "cat /sys/block/DEV/queue/scheduler" - the list of valid names
+will be displayed, with the currently selected scheduler in brackets::
+
+  # cat /sys/block/sda/queue/scheduler
+  [mq-deadline] kyber bfq none
+  # echo none >/sys/block/sda/queue/scheduler
+  # cat /sys/block/sda/queue/scheduler
+  [none] mq-deadline kyber bfq
diff --git a/Documentation/block/ublk.rst b/Documentation/block/ublk.rst
new file mode 100644
index 000000000..ba45c46cc
--- /dev/null
+++ b/Documentation/block/ublk.rst
@@ -0,0 +1,289 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===========================================
+Userspace block device driver (ublk driver)
+===========================================
+
+Overview
+========
+
+ublk is a generic framework for implementing block device logic from userspace.
+The motivation behind it is that moving virtual block drivers into userspace,
+such as loop, nbd and similar can be very helpful. It can help to implement
+new virtual block device such as ublk-qcow2 (there are several attempts of
+implementing qcow2 driver in kernel).
+
+Userspace block devices are attractive because:
+
+- They can be written many programming languages.
+- They can use libraries that are not available in the kernel.
+- They can be debugged with tools familiar to application developers.
+- Crashes do not kernel panic the machine.
+- Bugs are likely to have a lower security impact than bugs in kernel
+  code.
+- They can be installed and updated independently of the kernel.
+- They can be used to simulate block device easily with user specified
+  parameters/setting for test/debug purpose
+
+ublk block device (``/dev/ublkb*``) is added by ublk driver. Any IO request
+on the device will be forwarded to ublk userspace program. For convenience,
+in this document, ``ublk server`` refers to generic ublk userspace
+program. ``ublksrv`` [#userspace]_ is one of such implementation. It
+provides ``libublksrv`` [#userspace_lib]_ library for developing specific
+user block device conveniently, while also generic type block device is
+included, such as loop and null. Richard W.M. Jones wrote userspace nbd device
+``nbdublk`` [#userspace_nbdublk]_  based on ``libublksrv`` [#userspace_lib]_.
+
+After the IO is handled by userspace, the result is committed back to the
+driver, thus completing the request cycle. This way, any specific IO handling
+logic is totally done by userspace, such as loop's IO handling, NBD's IO
+communication, or qcow2's IO mapping.
+
+``/dev/ublkb*`` is driven by blk-mq request-based driver. Each request is
+assigned by one queue wide unique tag. ublk server assigns unique tag to each
+IO too, which is 1:1 mapped with IO of ``/dev/ublkb*``.
+
+Both the IO request forward and IO handling result committing are done via
+``io_uring`` passthrough command; that is why ublk is also one io_uring based
+block driver. It has been observed that using io_uring passthrough command can
+give better IOPS than block IO; which is why ublk is one of high performance
+implementation of userspace block device: not only IO request communication is
+done by io_uring, but also the preferred IO handling in ublk server is io_uring
+based approach too.
+
+ublk provides control interface to set/get ublk block device parameters.
+The interface is extendable and kabi compatible: basically any ublk request
+queue's parameter or ublk generic feature parameters can be set/get via the
+interface. Thus, ublk is generic userspace block device framework.
+For example, it is easy to setup a ublk device with specified block
+parameters from userspace.
+
+Using ublk
+==========
+
+ublk requires userspace ublk server to handle real block device logic.
+
+Below is example of using ``ublksrv`` to provide ublk-based loop device.
+
+- add a device::
+
+     ublk add -t loop -f ublk-loop.img
+
+- format with xfs, then use it::
+
+     mkfs.xfs /dev/ublkb0
+     mount /dev/ublkb0 /mnt
+     # do anything. all IOs are handled by io_uring
+     ...
+     umount /mnt
+
+- list the devices with their info::
+
+     ublk list
+
+- delete the device::
+
+     ublk del -a
+     ublk del -n $ublk_dev_id
+
+See usage details in README of ``ublksrv`` [#userspace_readme]_.
+
+Design
+======
+
+Control plane
+-------------
+
+ublk driver provides global misc device node (``/dev/ublk-control``) for
+managing and controlling ublk devices with help of several control commands:
+
+- ``UBLK_CMD_ADD_DEV``
+
+  Add a ublk char device (``/dev/ublkc*``) which is talked with ublk server
+  WRT IO command communication. Basic device info is sent together with this
+  command. It sets UAPI structure of ``ublksrv_ctrl_dev_info``,
+  such as ``nr_hw_queues``, ``queue_depth``, and max IO request buffer size,
+  for which the info is negotiated with the driver and sent back to the server.
+  When this command is completed, the basic device info is immutable.
+
+- ``UBLK_CMD_SET_PARAMS`` / ``UBLK_CMD_GET_PARAMS``
+
+  Set or get parameters of the device, which can be either generic feature
+  related, or request queue limit related, but can't be IO logic specific,
+  because the driver does not handle any IO logic. This command has to be
+  sent before sending ``UBLK_CMD_START_DEV``.
+
+- ``UBLK_CMD_START_DEV``
+
+  After the server prepares userspace resources (such as creating per-queue
+  pthread & io_uring for handling ublk IO), this command is sent to the
+  driver for allocating & exposing ``/dev/ublkb*``. Parameters set via
+  ``UBLK_CMD_SET_PARAMS`` are applied for creating the device.
+
+- ``UBLK_CMD_STOP_DEV``
+
+  Halt IO on ``/dev/ublkb*`` and remove the device. When this command returns,
+  ublk server will release resources (such as destroying per-queue pthread &
+  io_uring).
+
+- ``UBLK_CMD_DEL_DEV``
+
+  Remove ``/dev/ublkc*``. When this command returns, the allocated ublk device
+  number can be reused.
+
+- ``UBLK_CMD_GET_QUEUE_AFFINITY``
+
+  When ``/dev/ublkc`` is added, the driver creates block layer tagset, so
+  that each queue's affinity info is available. The server sends
+  ``UBLK_CMD_GET_QUEUE_AFFINITY`` to retrieve queue affinity info. It can
+  set up the per-queue context efficiently, such as bind affine CPUs with IO
+  pthread and try to allocate buffers in IO thread context.
+
+- ``UBLK_CMD_GET_DEV_INFO``
+
+  For retrieving device info via ``ublksrv_ctrl_dev_info``. It is the server's
+  responsibility to save IO target specific info in userspace.
+
+- ``UBLK_CMD_START_USER_RECOVERY``
+
+  This command is valid if ``UBLK_F_USER_RECOVERY`` feature is enabled. This
+  command is accepted after the old process has exited, ublk device is quiesced
+  and ``/dev/ublkc*`` is released. User should send this command before he starts
+  a new process which re-opens ``/dev/ublkc*``. When this command returns, the
+  ublk device is ready for the new process.
+
+- ``UBLK_CMD_END_USER_RECOVERY``
+
+  This command is valid if ``UBLK_F_USER_RECOVERY`` feature is enabled. This
+  command is accepted after ublk device is quiesced and a new process has
+  opened ``/dev/ublkc*`` and get all ublk queues be ready. When this command
+  returns, ublk device is unquiesced and new I/O requests are passed to the
+  new process.
+
+- user recovery feature description
+
+  Two new features are added for user recovery: ``UBLK_F_USER_RECOVERY`` and
+  ``UBLK_F_USER_RECOVERY_REISSUE``.
+
+  With ``UBLK_F_USER_RECOVERY`` set, after one ubq_daemon(ublk server's io
+  handler) is dying, ublk does not delete ``/dev/ublkb*`` during the whole
+  recovery stage and ublk device ID is kept. It is ublk server's
+  responsibility to recover the device context by its own knowledge.
+  Requests which have not been issued to userspace are requeued. Requests
+  which have been issued to userspace are aborted.
+
+  With ``UBLK_F_USER_RECOVERY_REISSUE`` set, after one ubq_daemon(ublk
+  server's io handler) is dying, contrary to ``UBLK_F_USER_RECOVERY``,
+  requests which have been issued to userspace are requeued and will be
+  re-issued to the new process after handling ``UBLK_CMD_END_USER_RECOVERY``.
+  ``UBLK_F_USER_RECOVERY_REISSUE`` is designed for backends who tolerate
+  double-write since the driver may issue the same I/O request twice. It
+  might be useful to a read-only FS or a VM backend.
+
+Data plane
+----------
+
+ublk server needs to create per-queue IO pthread & io_uring for handling IO
+commands via io_uring passthrough. The per-queue IO pthread
+focuses on IO handling and shouldn't handle any control & management
+tasks.
+
+The's IO is assigned by a unique tag, which is 1:1 mapping with IO
+request of ``/dev/ublkb*``.
+
+UAPI structure of ``ublksrv_io_desc`` is defined for describing each IO from
+the driver. A fixed mmaped area (array) on ``/dev/ublkc*`` is provided for
+exporting IO info to the server; such as IO offset, length, OP/flags and
+buffer address. Each ``ublksrv_io_desc`` instance can be indexed via queue id
+and IO tag directly.
+
+The following IO commands are communicated via io_uring passthrough command,
+and each command is only for forwarding the IO and committing the result
+with specified IO tag in the command data:
+
+- ``UBLK_IO_FETCH_REQ``
+
+  Sent from the server IO pthread for fetching future incoming IO requests
+  destined to ``/dev/ublkb*``. This command is sent only once from the server
+  IO pthread for ublk driver to setup IO forward environment.
+
+- ``UBLK_IO_COMMIT_AND_FETCH_REQ``
+
+  When an IO request is destined to ``/dev/ublkb*``, the driver stores
+  the IO's ``ublksrv_io_desc`` to the specified mapped area; then the
+  previous received IO command of this IO tag (either ``UBLK_IO_FETCH_REQ``
+  or ``UBLK_IO_COMMIT_AND_FETCH_REQ)`` is completed, so the server gets
+  the IO notification via io_uring.
+
+  After the server handles the IO, its result is committed back to the
+  driver by sending ``UBLK_IO_COMMIT_AND_FETCH_REQ`` back. Once ublkdrv
+  received this command, it parses the result and complete the request to
+  ``/dev/ublkb*``. In the meantime setup environment for fetching future
+  requests with the same IO tag. That is, ``UBLK_IO_COMMIT_AND_FETCH_REQ``
+  is reused for both fetching request and committing back IO result.
+
+- ``UBLK_IO_NEED_GET_DATA``
+
+  With ``UBLK_F_NEED_GET_DATA`` enabled, the WRITE request will be firstly
+  issued to ublk server without data copy. Then, IO backend of ublk server
+  receives the request and it can allocate data buffer and embed its addr
+  inside this new io command. After the kernel driver gets the command,
+  data copy is done from request pages to this backend's buffer. Finally,
+  backend receives the request again with data to be written and it can
+  truly handle the request.
+
+  ``UBLK_IO_NEED_GET_DATA`` adds one additional round-trip and one
+  io_uring_enter() syscall. Any user thinks that it may lower performance
+  should not enable UBLK_F_NEED_GET_DATA. ublk server pre-allocates IO
+  buffer for each IO by default. Any new project should try to use this
+  buffer to communicate with ublk driver. However, existing project may
+  break or not able to consume the new buffer interface; that's why this
+  command is added for backwards compatibility so that existing projects
+  can still consume existing buffers.
+
+- data copy between ublk server IO buffer and ublk block IO request
+
+  The driver needs to copy the block IO request pages into the server buffer
+  (pages) first for WRITE before notifying the server of the coming IO, so
+  that the server can handle WRITE request.
+
+  When the server handles READ request and sends
+  ``UBLK_IO_COMMIT_AND_FETCH_REQ`` to the server, ublkdrv needs to copy
+  the server buffer (pages) read to the IO request pages.
+
+Future development
+==================
+
+Container-aware ublk deivice
+----------------------------
+
+ublk driver doesn't handle any IO logic. Its function is well defined
+for now and very limited userspace interfaces are needed, which is also
+well defined too. It is possible to make ublk devices container-aware block
+devices in future as Stefan Hajnoczi suggested [#stefan]_, by removing
+ADMIN privilege.
+
+Zero copy
+---------
+
+Zero copy is a generic requirement for nbd, fuse or similar drivers. A
+problem [#xiaoguang]_ Xiaoguang mentioned is that pages mapped to userspace
+can't be remapped any more in kernel with existing mm interfaces. This can
+occurs when destining direct IO to ``/dev/ublkb*``. Also, he reported that
+big requests (IO size >= 256 KB) may benefit a lot from zero copy.
+
+
+References
+==========
+
+.. [#userspace] https://github.com/ming1/ubdsrv
+
+.. [#userspace_lib] https://github.com/ming1/ubdsrv/tree/master/lib
+
+.. [#userspace_nbdublk] https://gitlab.com/rwmjones/libnbd/-/tree/nbdublk
+
+.. [#userspace_readme] https://github.com/ming1/ubdsrv/blob/master/README
+
+.. [#stefan] https://lore.kernel.org/linux-block/YoOr6jBfgVm8GvWg@stefanha-x1.localdomain/
+
+.. [#xiaoguang] https://lore.kernel.org/linux-block/YoOr6jBfgVm8GvWg@stefanha-x1.localdomain/
diff --git a/Documentation/block/writeback_cache_control.rst b/Documentation/block/writeback_cache_control.rst
new file mode 100644
index 000000000..b208488d0
--- /dev/null
+++ b/Documentation/block/writeback_cache_control.rst
@@ -0,0 +1,86 @@
+==========================================
+Explicit volatile write back cache control
+==========================================
+
+Introduction
+------------
+
+Many storage devices, especially in the consumer market, come with volatile
+write back caches.  That means the devices signal I/O completion to the
+operating system before data actually has hit the non-volatile storage.  This
+behavior obviously speeds up various workloads, but it means the operating
+system needs to force data out to the non-volatile storage when it performs
+a data integrity operation like fsync, sync or an unmount.
+
+The Linux block layer provides two simple mechanisms that let filesystems
+control the caching behavior of the storage device.  These mechanisms are
+a forced cache flush, and the Force Unit Access (FUA) flag for requests.
+
+
+Explicit cache flushes
+----------------------
+
+The REQ_PREFLUSH flag can be OR ed into the r/w flags of a bio submitted from
+the filesystem and will make sure the volatile cache of the storage device
+has been flushed before the actual I/O operation is started.  This explicitly
+guarantees that previously completed write requests are on non-volatile
+storage before the flagged bio starts. In addition the REQ_PREFLUSH flag can be
+set on an otherwise empty bio structure, which causes only an explicit cache
+flush without any dependent I/O.  It is recommend to use
+the blkdev_issue_flush() helper for a pure cache flush.
+
+
+Forced Unit Access
+------------------
+
+The REQ_FUA flag can be OR ed into the r/w flags of a bio submitted from the
+filesystem and will make sure that I/O completion for this request is only
+signaled after the data has been committed to non-volatile storage.
+
+
+Implementation details for filesystems
+--------------------------------------
+
+Filesystems can simply set the REQ_PREFLUSH and REQ_FUA bits and do not have to
+worry if the underlying devices need any explicit cache flushing and how
+the Forced Unit Access is implemented.  The REQ_PREFLUSH and REQ_FUA flags
+may both be set on a single bio.
+
+
+Implementation details for bio based block drivers
+--------------------------------------------------------------
+
+These drivers will always see the REQ_PREFLUSH and REQ_FUA bits as they sit
+directly below the submit_bio interface.  For remapping drivers the REQ_FUA
+bits need to be propagated to underlying devices, and a global flush needs
+to be implemented for bios with the REQ_PREFLUSH bit set.  For real device
+drivers that do not have a volatile cache the REQ_PREFLUSH and REQ_FUA bits
+on non-empty bios can simply be ignored, and REQ_PREFLUSH requests without
+data can be completed successfully without doing any work.  Drivers for
+devices with volatile caches need to implement the support for these
+flags themselves without any help from the block layer.
+
+
+Implementation details for request_fn based block drivers
+---------------------------------------------------------
+
+For devices that do not support volatile write caches there is no driver
+support required, the block layer completes empty REQ_PREFLUSH requests before
+entering the driver and strips off the REQ_PREFLUSH and REQ_FUA bits from
+requests that have a payload.  For devices with volatile write caches the
+driver needs to tell the block layer that it supports flushing caches by
+doing::
+
+	blk_queue_write_cache(sdkp->disk->queue, true, false);
+
+and handle empty REQ_OP_FLUSH requests in its prep_fn/request_fn.  Note that
+REQ_PREFLUSH requests with a payload are automatically turned into a sequence
+of an empty REQ_OP_FLUSH request followed by the actual write by the block
+layer.  For devices that also support the FUA bit the block layer needs
+to be told to pass through the REQ_FUA bit using::
+
+	blk_queue_write_cache(sdkp->disk->queue, true, true);
+
+and the driver must handle write requests that have the REQ_FUA bit set
+in prep_fn/request_fn.  If the FUA bit is not natively supported the block
+layer turns it into an empty REQ_OP_FLUSH request after the actual write.