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-rw-r--r--Documentation/admin-guide/blockdev/drbd/DRBD-8.3-data-packets.svg588
-rw-r--r--Documentation/admin-guide/blockdev/drbd/DRBD-data-packets.svg459
-rw-r--r--Documentation/admin-guide/blockdev/drbd/conn-states-8.dot18
-rw-r--r--Documentation/admin-guide/blockdev/drbd/data-structure-v9.rst42
-rw-r--r--Documentation/admin-guide/blockdev/drbd/disk-states-8.dot16
-rw-r--r--Documentation/admin-guide/blockdev/drbd/drbd-connection-state-overview.dot85
-rw-r--r--Documentation/admin-guide/blockdev/drbd/figures.rst30
-rw-r--r--Documentation/admin-guide/blockdev/drbd/index.rst19
-rw-r--r--Documentation/admin-guide/blockdev/drbd/peer-states-8.dot8
-rw-r--r--Documentation/admin-guide/blockdev/floppy.rst255
-rw-r--r--Documentation/admin-guide/blockdev/index.rst16
-rw-r--r--Documentation/admin-guide/blockdev/nbd.rst31
-rw-r--r--Documentation/admin-guide/blockdev/paride.rst439
-rw-r--r--Documentation/admin-guide/blockdev/ramdisk.rst153
-rw-r--r--Documentation/admin-guide/blockdev/zram.rst440
15 files changed, 2599 insertions, 0 deletions
diff --git a/Documentation/admin-guide/blockdev/drbd/DRBD-8.3-data-packets.svg b/Documentation/admin-guide/blockdev/drbd/DRBD-8.3-data-packets.svg
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+ style="font-size:318px;font-weight:400;fill:#000000;visibility:visible;font-family:Helvetica embedded">
+ <tspan
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+ style="font-size:318px;font-weight:400;fill:#000000;visibility:visible;font-family:Helvetica embedded">
+ <tspan
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+ id="text1149"
+ style="font-size:318px;font-weight:400;fill:#000000;visibility:visible;font-family:Helvetica embedded">
+ <tspan
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+ <tspan
+ x="1426 1532 1693 1871 2031 2209 2472 2649 2721 2899 2988 3166 3344 3416 3593 3699"
+ y="11302"
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+ style="font-size:318px;font-weight:400;fill:#000000;visibility:visible;font-family:Helvetica embedded">
+ <tspan
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+ <tspan
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+ style="font-size:318px;font-weight:400;fill:#000000;visibility:visible;font-family:Helvetica embedded">
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+ style="font-size:318px;font-weight:400;fill:#000000;visibility:visible;font-family:Helvetica embedded">
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diff --git a/Documentation/admin-guide/blockdev/drbd/DRBD-data-packets.svg b/Documentation/admin-guide/blockdev/drbd/DRBD-data-packets.svg
new file mode 100644
index 000000000..48a1e2165
--- /dev/null
+++ b/Documentation/admin-guide/blockdev/drbd/DRBD-data-packets.svg
@@ -0,0 +1,459 @@
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+ <tspan
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+ <tspan
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+ y="7606"
+ id="tspan589">drbd_endio_write_sec()</tspan>
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+ style="font-size:318px;font-weight:400;fill:#008000;visibility:visible;font-family:Helvetica embedded">
+ <tspan
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+ <tspan
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+ style="font-size:423px;font-weight:400;fill:#000000;visibility:visible;font-family:Helvetica embedded">
+ <tspan
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+ <tspan
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+ style="font-size:318px;font-weight:400;fill:#008000;visibility:visible;font-family:Helvetica embedded">
+ <tspan
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+ style="font-size:318px;font-weight:400;fill:#008000;visibility:visible;font-family:Helvetica embedded">
+ <tspan
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+ <tspan
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+ style="font-size:318px;font-weight:400;fill:#000000;visibility:visible;font-family:Helvetica embedded">
+ <tspan
+ x="1632 1810 1882 2060 2220 2398 2661 2839 2910 3088 3177 3355 3533 3605 3783 3888"
+ y="7331"
+ id="tspan965">al_complete_io()</tspan>
+ </text>
+ <text
+ id="text979"
+ style="font-size:318px;font-weight:400;fill:#000000;visibility:visible;font-family:Helvetica embedded">
+ <tspan
+ x="2126 2232 2393 2571 2748 2926 3104 3176 3354 3531 3603 3781 3887"
+ y="17431"
+ id="tspan981">rs_begin_io()</tspan>
+ </text>
+ <text
+ id="text995"
+ style="font-size:318px;font-weight:400;fill:#000000;visibility:visible;font-family:Helvetica embedded">
+ <tspan
+ x="1626 1732 1893 2071 2231 2409 2672 2849 2921 3099 3188 3366 3544 3616 3793 3899"
+ y="22331"
+ id="tspan997">rs_complete_io()</tspan>
+ </text>
+ <text
+ id="text1011"
+ style="font-size:318px;font-weight:400;fill:#000000;visibility:visible;font-family:Helvetica embedded">
+ <tspan
+ x="16027 16133 16294 16472 16649 16827 17005 17077 17255 17432 17504 17682 17788"
+ y="18402"
+ id="tspan1013">rs_begin_io()</tspan>
+ </text>
+ <text
+ id="text1027"
+ style="font-size:318px;font-weight:400;fill:#000000;visibility:visible;font-family:Helvetica embedded">
+ <tspan
+ x="16115 16221 16382 16560 16720 16898 17161 17338 17410 17588 17677 17855 18033 18105 18282 18388"
+ y="20331"
+ id="tspan1029">rs_complete_io()</tspan>
+ </text>
+</svg>
diff --git a/Documentation/admin-guide/blockdev/drbd/conn-states-8.dot b/Documentation/admin-guide/blockdev/drbd/conn-states-8.dot
new file mode 100644
index 000000000..025e8cf5e
--- /dev/null
+++ b/Documentation/admin-guide/blockdev/drbd/conn-states-8.dot
@@ -0,0 +1,18 @@
+digraph conn_states {
+ StandAllone -> WFConnection [ label = "ioctl_set_net()" ]
+ WFConnection -> Unconnected [ label = "unable to bind()" ]
+ WFConnection -> WFReportParams [ label = "in connect() after accept" ]
+ WFReportParams -> StandAllone [ label = "checks in receive_param()" ]
+ WFReportParams -> Connected [ label = "in receive_param()" ]
+ WFReportParams -> WFBitMapS [ label = "sync_handshake()" ]
+ WFReportParams -> WFBitMapT [ label = "sync_handshake()" ]
+ WFBitMapS -> SyncSource [ label = "receive_bitmap()" ]
+ WFBitMapT -> SyncTarget [ label = "receive_bitmap()" ]
+ SyncSource -> Connected
+ SyncTarget -> Connected
+ SyncSource -> PausedSyncS
+ SyncTarget -> PausedSyncT
+ PausedSyncS -> SyncSource
+ PausedSyncT -> SyncTarget
+ Connected -> WFConnection [ label = "* on network error" ]
+}
diff --git a/Documentation/admin-guide/blockdev/drbd/data-structure-v9.rst b/Documentation/admin-guide/blockdev/drbd/data-structure-v9.rst
new file mode 100644
index 000000000..66036b901
--- /dev/null
+++ b/Documentation/admin-guide/blockdev/drbd/data-structure-v9.rst
@@ -0,0 +1,42 @@
+================================
+kernel data structure for DRBD-9
+================================
+
+This describes the in kernel data structure for DRBD-9. Starting with
+Linux v3.14 we are reorganizing DRBD to use this data structure.
+
+Basic Data Structure
+====================
+
+A node has a number of DRBD resources. Each such resource has a number of
+devices (aka volumes) and connections to other nodes ("peer nodes"). Each DRBD
+device is represented by a block device locally.
+
+The DRBD objects are interconnected to form a matrix as depicted below; a
+drbd_peer_device object sits at each intersection between a drbd_device and a
+drbd_connection::
+
+ /--------------+---------------+.....+---------------\
+ | resource | device | | device |
+ +--------------+---------------+.....+---------------+
+ | connection | peer_device | | peer_device |
+ +--------------+---------------+.....+---------------+
+ : : : : :
+ : : : : :
+ +--------------+---------------+.....+---------------+
+ | connection | peer_device | | peer_device |
+ \--------------+---------------+.....+---------------/
+
+In this table, horizontally, devices can be accessed from resources by their
+volume number. Likewise, peer_devices can be accessed from connections by
+their volume number. Objects in the vertical direction are connected by double
+linked lists. There are back pointers from peer_devices to their connections a
+devices, and from connections and devices to their resource.
+
+All resources are in the drbd_resources double-linked list. In addition, all
+devices can be accessed by their minor device number via the drbd_devices idr.
+
+The drbd_resource, drbd_connection, and drbd_device objects are reference
+counted. The peer_device objects only serve to establish the links between
+devices and connections; their lifetime is determined by the lifetime of the
+device and connection which they reference.
diff --git a/Documentation/admin-guide/blockdev/drbd/disk-states-8.dot b/Documentation/admin-guide/blockdev/drbd/disk-states-8.dot
new file mode 100644
index 000000000..d06cfb46f
--- /dev/null
+++ b/Documentation/admin-guide/blockdev/drbd/disk-states-8.dot
@@ -0,0 +1,16 @@
+digraph disk_states {
+ Diskless -> Inconsistent [ label = "ioctl_set_disk()" ]
+ Diskless -> Consistent [ label = "ioctl_set_disk()" ]
+ Diskless -> Outdated [ label = "ioctl_set_disk()" ]
+ Consistent -> Outdated [ label = "receive_param()" ]
+ Consistent -> UpToDate [ label = "receive_param()" ]
+ Consistent -> Inconsistent [ label = "start resync" ]
+ Outdated -> Inconsistent [ label = "start resync" ]
+ UpToDate -> Inconsistent [ label = "ioctl_replicate" ]
+ Inconsistent -> UpToDate [ label = "resync completed" ]
+ Consistent -> Failed [ label = "io completion error" ]
+ Outdated -> Failed [ label = "io completion error" ]
+ UpToDate -> Failed [ label = "io completion error" ]
+ Inconsistent -> Failed [ label = "io completion error" ]
+ Failed -> Diskless [ label = "sending notify to peer" ]
+}
diff --git a/Documentation/admin-guide/blockdev/drbd/drbd-connection-state-overview.dot b/Documentation/admin-guide/blockdev/drbd/drbd-connection-state-overview.dot
new file mode 100644
index 000000000..6d9cf0a7b
--- /dev/null
+++ b/Documentation/admin-guide/blockdev/drbd/drbd-connection-state-overview.dot
@@ -0,0 +1,85 @@
+// vim: set sw=2 sts=2 :
+digraph {
+ rankdir=BT
+ bgcolor=white
+
+ node [shape=plaintext]
+ node [fontcolor=black]
+
+ StandAlone [ style=filled,fillcolor=gray,label=StandAlone ]
+
+ node [fontcolor=lightgray]
+
+ Unconnected [ label=Unconnected ]
+
+ CommTrouble [ shape=record,
+ label="{communication loss|{Timeout|BrokenPipe|NetworkFailure}}" ]
+
+ node [fontcolor=gray]
+
+ subgraph cluster_try_connect {
+ label="try to connect, handshake"
+ rank=max
+ WFConnection [ label=WFConnection ]
+ WFReportParams [ label=WFReportParams ]
+ }
+
+ TearDown [ label=TearDown ]
+
+ Connected [ label=Connected,style=filled,fillcolor=green,fontcolor=black ]
+
+ node [fontcolor=lightblue]
+
+ StartingSyncS [ label=StartingSyncS ]
+ StartingSyncT [ label=StartingSyncT ]
+
+ subgraph cluster_bitmap_exchange {
+ node [fontcolor=red]
+ fontcolor=red
+ label="new application (WRITE?) requests blocked\lwhile bitmap is exchanged"
+
+ WFBitMapT [ label=WFBitMapT ]
+ WFSyncUUID [ label=WFSyncUUID ]
+ WFBitMapS [ label=WFBitMapS ]
+ }
+
+ node [fontcolor=blue]
+
+ cluster_resync [ shape=record,label="{<any>resynchronisation process running\l'concurrent' application requests allowed|{{<T>PausedSyncT\nSyncTarget}|{<S>PausedSyncS\nSyncSource}}}" ]
+
+ node [shape=box,fontcolor=black]
+
+ // drbdadm [label="drbdadm connect"]
+ // handshake [label="drbd_connect()\ndrbd_do_handshake\ndrbd_sync_handshake() etc."]
+ // comm_error [label="communication trouble"]
+
+ //
+ // edges
+ // --------------------------------------
+
+ StandAlone -> Unconnected [ label="drbdadm connect" ]
+ Unconnected -> StandAlone [ label="drbdadm disconnect\lor serious communication trouble" ]
+ Unconnected -> WFConnection [ label="receiver thread is started" ]
+ WFConnection -> WFReportParams [ headlabel="accept()\land/or \lconnect()\l" ]
+
+ WFReportParams -> StandAlone [ label="during handshake\lpeers do not agree\labout something essential" ]
+ WFReportParams -> Connected [ label="data identical\lno sync needed",color=green,fontcolor=green ]
+
+ WFReportParams -> WFBitMapS
+ WFReportParams -> WFBitMapT
+ WFBitMapT -> WFSyncUUID [minlen=0.1,constraint=false]
+
+ WFBitMapS -> cluster_resync:S
+ WFSyncUUID -> cluster_resync:T
+
+ edge [color=green]
+ cluster_resync:any -> Connected [ label="resnyc done",fontcolor=green ]
+
+ edge [color=red]
+ WFReportParams -> CommTrouble
+ Connected -> CommTrouble
+ cluster_resync:any -> CommTrouble
+ edge [color=black]
+ CommTrouble -> Unconnected [label="receiver thread is stopped" ]
+
+}
diff --git a/Documentation/admin-guide/blockdev/drbd/figures.rst b/Documentation/admin-guide/blockdev/drbd/figures.rst
new file mode 100644
index 000000000..9f73253ea
--- /dev/null
+++ b/Documentation/admin-guide/blockdev/drbd/figures.rst
@@ -0,0 +1,30 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. The here included files are intended to help understand the implementation
+
+Data flows that Relate some functions, and write packets
+========================================================
+
+.. kernel-figure:: DRBD-8.3-data-packets.svg
+ :alt: DRBD-8.3-data-packets.svg
+ :align: center
+
+.. kernel-figure:: DRBD-data-packets.svg
+ :alt: DRBD-data-packets.svg
+ :align: center
+
+
+Sub graphs of DRBD's state transitions
+======================================
+
+.. kernel-figure:: conn-states-8.dot
+ :alt: conn-states-8.dot
+ :align: center
+
+.. kernel-figure:: disk-states-8.dot
+ :alt: disk-states-8.dot
+ :align: center
+
+.. kernel-figure:: peer-states-8.dot
+ :alt: peer-states-8.dot
+ :align: center
diff --git a/Documentation/admin-guide/blockdev/drbd/index.rst b/Documentation/admin-guide/blockdev/drbd/index.rst
new file mode 100644
index 000000000..561fd1e35
--- /dev/null
+++ b/Documentation/admin-guide/blockdev/drbd/index.rst
@@ -0,0 +1,19 @@
+==========================================
+Distributed Replicated Block Device - DRBD
+==========================================
+
+Description
+===========
+
+ DRBD is a shared-nothing, synchronously replicated block device. It
+ is designed to serve as a building block for high availability
+ clusters and in this context, is a "drop-in" replacement for shared
+ storage. Simplistically, you could see it as a network RAID 1.
+
+ Please visit https://www.drbd.org to find out more.
+
+.. toctree::
+ :maxdepth: 1
+
+ data-structure-v9
+ figures
diff --git a/Documentation/admin-guide/blockdev/drbd/peer-states-8.dot b/Documentation/admin-guide/blockdev/drbd/peer-states-8.dot
new file mode 100644
index 000000000..6dc395495
--- /dev/null
+++ b/Documentation/admin-guide/blockdev/drbd/peer-states-8.dot
@@ -0,0 +1,8 @@
+digraph peer_states {
+ Secondary -> Primary [ label = "recv state packet" ]
+ Primary -> Secondary [ label = "recv state packet" ]
+ Primary -> Unknown [ label = "connection lost" ]
+ Secondary -> Unknown [ label = "connection lost" ]
+ Unknown -> Primary [ label = "connected" ]
+ Unknown -> Secondary [ label = "connected" ]
+}
diff --git a/Documentation/admin-guide/blockdev/floppy.rst b/Documentation/admin-guide/blockdev/floppy.rst
new file mode 100644
index 000000000..0328438eb
--- /dev/null
+++ b/Documentation/admin-guide/blockdev/floppy.rst
@@ -0,0 +1,255 @@
+=============
+Floppy Driver
+=============
+
+FAQ list:
+=========
+
+A FAQ list may be found in the fdutils package (see below), and also
+at <https://fdutils.linux.lu/faq.html>.
+
+
+LILO configuration options (Thinkpad users, read this)
+======================================================
+
+The floppy driver is configured using the 'floppy=' option in
+lilo. This option can be typed at the boot prompt, or entered in the
+lilo configuration file.
+
+Example: If your kernel is called linux-2.6.9, type the following line
+at the lilo boot prompt (if you have a thinkpad)::
+
+ linux-2.6.9 floppy=thinkpad
+
+You may also enter the following line in /etc/lilo.conf, in the description
+of linux-2.6.9::
+
+ append = "floppy=thinkpad"
+
+Several floppy related options may be given, example::
+
+ linux-2.6.9 floppy=daring floppy=two_fdc
+ append = "floppy=daring floppy=two_fdc"
+
+If you give options both in the lilo config file and on the boot
+prompt, the option strings of both places are concatenated, the boot
+prompt options coming last. That's why there are also options to
+restore the default behavior.
+
+
+Module configuration options
+============================
+
+If you use the floppy driver as a module, use the following syntax::
+
+ modprobe floppy floppy="<options>"
+
+Example::
+
+ modprobe floppy floppy="omnibook messages"
+
+If you need certain options enabled every time you load the floppy driver,
+you can put::
+
+ options floppy floppy="omnibook messages"
+
+in a configuration file in /etc/modprobe.d/.
+
+
+The floppy driver related options are:
+
+ floppy=asus_pci
+ Sets the bit mask to allow only units 0 and 1. (default)
+
+ floppy=daring
+ Tells the floppy driver that you have a well behaved floppy controller.
+ This allows more efficient and smoother operation, but may fail on
+ certain controllers. This may speed up certain operations.
+
+ floppy=0,daring
+ Tells the floppy driver that your floppy controller should be used
+ with caution.
+
+ floppy=one_fdc
+ Tells the floppy driver that you have only one floppy controller.
+ (default)
+
+ floppy=two_fdc / floppy=<address>,two_fdc
+ Tells the floppy driver that you have two floppy controllers.
+ The second floppy controller is assumed to be at <address>.
+ This option is not needed if the second controller is at address
+ 0x370, and if you use the 'cmos' option.
+
+ floppy=thinkpad
+ Tells the floppy driver that you have a Thinkpad. Thinkpads use an
+ inverted convention for the disk change line.
+
+ floppy=0,thinkpad
+ Tells the floppy driver that you don't have a Thinkpad.
+
+ floppy=omnibook / floppy=nodma
+ Tells the floppy driver not to use Dma for data transfers.
+ This is needed on HP Omnibooks, which don't have a workable
+ DMA channel for the floppy driver. This option is also useful
+ if you frequently get "Unable to allocate DMA memory" messages.
+ Indeed, dma memory needs to be continuous in physical memory,
+ and is thus harder to find, whereas non-dma buffers may be
+ allocated in virtual memory. However, I advise against this if
+ you have an FDC without a FIFO (8272A or 82072). 82072A and
+ later are OK. You also need at least a 486 to use nodma.
+ If you use nodma mode, I suggest you also set the FIFO
+ threshold to 10 or lower, in order to limit the number of data
+ transfer interrupts.
+
+ If you have a FIFO-able FDC, the floppy driver automatically
+ falls back on non DMA mode if no DMA-able memory can be found.
+ If you want to avoid this, explicitly ask for 'yesdma'.
+
+ floppy=yesdma
+ Tells the floppy driver that a workable DMA channel is available.
+ (default)
+
+ floppy=nofifo
+ Disables the FIFO entirely. This is needed if you get "Bus
+ master arbitration error" messages from your Ethernet card (or
+ from other devices) while accessing the floppy.
+
+ floppy=usefifo
+ Enables the FIFO. (default)
+
+ floppy=<threshold>,fifo_depth
+ Sets the FIFO threshold. This is mostly relevant in DMA
+ mode. If this is higher, the floppy driver tolerates more
+ interrupt latency, but it triggers more interrupts (i.e. it
+ imposes more load on the rest of the system). If this is
+ lower, the interrupt latency should be lower too (faster
+ processor). The benefit of a lower threshold is less
+ interrupts.
+
+ To tune the fifo threshold, switch on over/underrun messages
+ using 'floppycontrol --messages'. Then access a floppy
+ disk. If you get a huge amount of "Over/Underrun - retrying"
+ messages, then the fifo threshold is too low. Try with a
+ higher value, until you only get an occasional Over/Underrun.
+ It is a good idea to compile the floppy driver as a module
+ when doing this tuning. Indeed, it allows to try different
+ fifo values without rebooting the machine for each test. Note
+ that you need to do 'floppycontrol --messages' every time you
+ re-insert the module.
+
+ Usually, tuning the fifo threshold should not be needed, as
+ the default (0xa) is reasonable.
+
+ floppy=<drive>,<type>,cmos
+ Sets the CMOS type of <drive> to <type>. This is mandatory if
+ you have more than two floppy drives (only two can be
+ described in the physical CMOS), or if your BIOS uses
+ non-standard CMOS types. The CMOS types are:
+
+ == ==================================
+ 0 Use the value of the physical CMOS
+ 1 5 1/4 DD
+ 2 5 1/4 HD
+ 3 3 1/2 DD
+ 4 3 1/2 HD
+ 5 3 1/2 ED
+ 6 3 1/2 ED
+ 16 unknown or not installed
+ == ==================================
+
+ (Note: there are two valid types for ED drives. This is because 5 was
+ initially chosen to represent floppy *tapes*, and 6 for ED drives.
+ AMI ignored this, and used 5 for ED drives. That's why the floppy
+ driver handles both.)
+
+ floppy=unexpected_interrupts
+ Print a warning message when an unexpected interrupt is received.
+ (default)
+
+ floppy=no_unexpected_interrupts / floppy=L40SX
+ Don't print a message when an unexpected interrupt is received. This
+ is needed on IBM L40SX laptops in certain video modes. (There seems
+ to be an interaction between video and floppy. The unexpected
+ interrupts affect only performance, and can be safely ignored.)
+
+ floppy=broken_dcl
+ Don't use the disk change line, but assume that the disk was
+ changed whenever the device node is reopened. Needed on some
+ boxes where the disk change line is broken or unsupported.
+ This should be regarded as a stopgap measure, indeed it makes
+ floppy operation less efficient due to unneeded cache
+ flushings, and slightly more unreliable. Please verify your
+ cable, connection and jumper settings if you have any DCL
+ problems. However, some older drives, and also some laptops
+ are known not to have a DCL.
+
+ floppy=debug
+ Print debugging messages.
+
+ floppy=messages
+ Print informational messages for some operations (disk change
+ notifications, warnings about over and underruns, and about
+ autodetection).
+
+ floppy=silent_dcl_clear
+ Uses a less noisy way to clear the disk change line (which
+ doesn't involve seeks). Implied by 'daring' option.
+
+ floppy=<nr>,irq
+ Sets the floppy IRQ to <nr> instead of 6.
+
+ floppy=<nr>,dma
+ Sets the floppy DMA channel to <nr> instead of 2.
+
+ floppy=slow
+ Use PS/2 stepping rate::
+
+ PS/2 floppies have much slower step rates than regular floppies.
+ It's been recommended that take about 1/4 of the default speed
+ in some more extreme cases.
+
+
+Supporting utilities and additional documentation:
+==================================================
+
+Additional parameters of the floppy driver can be configured at
+runtime. Utilities which do this can be found in the fdutils package.
+This package also contains a new version of mtools which allows to
+access high capacity disks (up to 1992K on a high density 3 1/2 disk!).
+It also contains additional documentation about the floppy driver.
+
+The latest version can be found at fdutils homepage:
+
+ https://fdutils.linux.lu
+
+The fdutils releases can be found at:
+
+ https://fdutils.linux.lu/download.html
+
+ http://www.tux.org/pub/knaff/fdutils/
+
+ ftp://metalab.unc.edu/pub/Linux/utils/disk-management/
+
+Reporting problems about the floppy driver
+==========================================
+
+If you have a question or a bug report about the floppy driver, mail
+me at Alain.Knaff@poboxes.com . If you post to Usenet, preferably use
+comp.os.linux.hardware. As the volume in these groups is rather high,
+be sure to include the word "floppy" (or "FLOPPY") in the subject
+line. If the reported problem happens when mounting floppy disks, be
+sure to mention also the type of the filesystem in the subject line.
+
+Be sure to read the FAQ before mailing/posting any bug reports!
+
+Alain
+
+Changelog
+=========
+
+10-30-2004 :
+ Cleanup, updating, add reference to module configuration.
+ James Nelson <james4765@gmail.com>
+
+6-3-2000 :
+ Original Document
diff --git a/Documentation/admin-guide/blockdev/index.rst b/Documentation/admin-guide/blockdev/index.rst
new file mode 100644
index 000000000..957ccf617
--- /dev/null
+++ b/Documentation/admin-guide/blockdev/index.rst
@@ -0,0 +1,16 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=============
+Block Devices
+=============
+
+.. toctree::
+ :maxdepth: 1
+
+ floppy
+ nbd
+ paride
+ ramdisk
+ zram
+
+ drbd/index
diff --git a/Documentation/admin-guide/blockdev/nbd.rst b/Documentation/admin-guide/blockdev/nbd.rst
new file mode 100644
index 000000000..d78dfe559
--- /dev/null
+++ b/Documentation/admin-guide/blockdev/nbd.rst
@@ -0,0 +1,31 @@
+==================================
+Network Block Device (TCP version)
+==================================
+
+1) Overview
+-----------
+
+What is it: With this compiled in the kernel (or as a module), Linux
+can use a remote server as one of its block devices. So every time
+the client computer wants to read, e.g., /dev/nb0, it sends a
+request over TCP to the server, which will reply with the data read.
+This can be used for stations with low disk space (or even diskless)
+to borrow disk space from another computer.
+Unlike NFS, it is possible to put any filesystem on it, etc.
+
+For more information, or to download the nbd-client and nbd-server
+tools, go to http://nbd.sf.net/.
+
+The nbd kernel module need only be installed on the client
+system, as the nbd-server is completely in userspace. In fact,
+the nbd-server has been successfully ported to other operating
+systems, including Windows.
+
+A) NBD parameters
+-----------------
+
+max_part
+ Number of partitions per device (default: 0).
+
+nbds_max
+ Number of block devices that should be initialized (default: 16).
diff --git a/Documentation/admin-guide/blockdev/paride.rst b/Documentation/admin-guide/blockdev/paride.rst
new file mode 100644
index 000000000..e1ce90af6
--- /dev/null
+++ b/Documentation/admin-guide/blockdev/paride.rst
@@ -0,0 +1,439 @@
+===================================
+Linux and parallel port IDE devices
+===================================
+
+PARIDE v1.03 (c) 1997-8 Grant Guenther <grant@torque.net>
+
+1. Introduction
+===============
+
+Owing to the simplicity and near universality of the parallel port interface
+to personal computers, many external devices such as portable hard-disk,
+CD-ROM, LS-120 and tape drives use the parallel port to connect to their
+host computer. While some devices (notably scanners) use ad-hoc methods
+to pass commands and data through the parallel port interface, most
+external devices are actually identical to an internal model, but with
+a parallel-port adapter chip added in. Some of the original parallel port
+adapters were little more than mechanisms for multiplexing a SCSI bus.
+(The Iomega PPA-3 adapter used in the ZIP drives is an example of this
+approach). Most current designs, however, take a different approach.
+The adapter chip reproduces a small ISA or IDE bus in the external device
+and the communication protocol provides operations for reading and writing
+device registers, as well as data block transfer functions. Sometimes,
+the device being addressed via the parallel cable is a standard SCSI
+controller like an NCR 5380. The "ditto" family of external tape
+drives use the ISA replicator to interface a floppy disk controller,
+which is then connected to a floppy-tape mechanism. The vast majority
+of external parallel port devices, however, are now based on standard
+IDE type devices, which require no intermediate controller. If one
+were to open up a parallel port CD-ROM drive, for instance, one would
+find a standard ATAPI CD-ROM drive, a power supply, and a single adapter
+that interconnected a standard PC parallel port cable and a standard
+IDE cable. It is usually possible to exchange the CD-ROM device with
+any other device using the IDE interface.
+
+The document describes the support in Linux for parallel port IDE
+devices. It does not cover parallel port SCSI devices, "ditto" tape
+drives or scanners. Many different devices are supported by the
+parallel port IDE subsystem, including:
+
+ - MicroSolutions backpack CD-ROM
+ - MicroSolutions backpack PD/CD
+ - MicroSolutions backpack hard-drives
+ - MicroSolutions backpack 8000t tape drive
+ - SyQuest EZ-135, EZ-230 & SparQ drives
+ - Avatar Shark
+ - Imation Superdisk LS-120
+ - Maxell Superdisk LS-120
+ - FreeCom Power CD
+ - Hewlett-Packard 5GB and 8GB tape drives
+ - Hewlett-Packard 7100 and 7200 CD-RW drives
+
+as well as most of the clone and no-name products on the market.
+
+To support such a wide range of devices, PARIDE, the parallel port IDE
+subsystem, is actually structured in three parts. There is a base
+paride module which provides a registry and some common methods for
+accessing the parallel ports. The second component is a set of
+high-level drivers for each of the different types of supported devices:
+
+ === =============
+ pd IDE disk
+ pcd ATAPI CD-ROM
+ pf ATAPI disk
+ pt ATAPI tape
+ pg ATAPI generic
+ === =============
+
+(Currently, the pg driver is only used with CD-R drives).
+
+The high-level drivers function according to the relevant standards.
+The third component of PARIDE is a set of low-level protocol drivers
+for each of the parallel port IDE adapter chips. Thanks to the interest
+and encouragement of Linux users from many parts of the world,
+support is available for almost all known adapter protocols:
+
+ ==== ====================================== ====
+ aten ATEN EH-100 (HK)
+ bpck Microsolutions backpack (US)
+ comm DataStor (old-type) "commuter" adapter (TW)
+ dstr DataStor EP-2000 (TW)
+ epat Shuttle EPAT (UK)
+ epia Shuttle EPIA (UK)
+ fit2 FIT TD-2000 (US)
+ fit3 FIT TD-3000 (US)
+ friq Freecom IQ cable (DE)
+ frpw Freecom Power (DE)
+ kbic KingByte KBIC-951A and KBIC-971A (TW)
+ ktti KT Technology PHd adapter (SG)
+ on20 OnSpec 90c20 (US)
+ on26 OnSpec 90c26 (US)
+ ==== ====================================== ====
+
+
+2. Using the PARIDE subsystem
+=============================
+
+While configuring the Linux kernel, you may choose either to build
+the PARIDE drivers into your kernel, or to build them as modules.
+
+In either case, you will need to select "Parallel port IDE device support"
+as well as at least one of the high-level drivers and at least one
+of the parallel port communication protocols. If you do not know
+what kind of parallel port adapter is used in your drive, you could
+begin by checking the file names and any text files on your DOS
+installation floppy. Alternatively, you can look at the markings on
+the adapter chip itself. That's usually sufficient to identify the
+correct device.
+
+You can actually select all the protocol modules, and allow the PARIDE
+subsystem to try them all for you.
+
+For the "brand-name" products listed above, here are the protocol
+and high-level drivers that you would use:
+
+ ================ ============ ====== ========
+ Manufacturer Model Driver Protocol
+ ================ ============ ====== ========
+ MicroSolutions CD-ROM pcd bpck
+ MicroSolutions PD drive pf bpck
+ MicroSolutions hard-drive pd bpck
+ MicroSolutions 8000t tape pt bpck
+ SyQuest EZ, SparQ pd epat
+ Imation Superdisk pf epat
+ Maxell Superdisk pf friq
+ Avatar Shark pd epat
+ FreeCom CD-ROM pcd frpw
+ Hewlett-Packard 5GB Tape pt epat
+ Hewlett-Packard 7200e (CD) pcd epat
+ Hewlett-Packard 7200e (CD-R) pg epat
+ ================ ============ ====== ========
+
+2.1 Configuring built-in drivers
+---------------------------------
+
+We recommend that you get to know how the drivers work and how to
+configure them as loadable modules, before attempting to compile a
+kernel with the drivers built-in.
+
+If you built all of your PARIDE support directly into your kernel,
+and you have just a single parallel port IDE device, your kernel should
+locate it automatically for you. If you have more than one device,
+you may need to give some command line options to your bootloader
+(eg: LILO), how to do that is beyond the scope of this document.
+
+The high-level drivers accept a number of command line parameters, all
+of which are documented in the source files in linux/drivers/block/paride.
+By default, each driver will automatically try all parallel ports it
+can find, and all protocol types that have been installed, until it finds
+a parallel port IDE adapter. Once it finds one, the probe stops. So,
+if you have more than one device, you will need to tell the drivers
+how to identify them. This requires specifying the port address, the
+protocol identification number and, for some devices, the drive's
+chain ID. While your system is booting, a number of messages are
+displayed on the console. Like all such messages, they can be
+reviewed with the 'dmesg' command. Among those messages will be
+some lines like::
+
+ paride: bpck registered as protocol 0
+ paride: epat registered as protocol 1
+
+The numbers will always be the same until you build a new kernel with
+different protocol selections. You should note these numbers as you
+will need them to identify the devices.
+
+If you happen to be using a MicroSolutions backpack device, you will
+also need to know the unit ID number for each drive. This is usually
+the last two digits of the drive's serial number (but read MicroSolutions'
+documentation about this).
+
+As an example, let's assume that you have a MicroSolutions PD/CD drive
+with unit ID number 36 connected to the parallel port at 0x378, a SyQuest
+EZ-135 connected to the chained port on the PD/CD drive and also an
+Imation Superdisk connected to port 0x278. You could give the following
+options on your boot command::
+
+ pd.drive0=0x378,1 pf.drive0=0x278,1 pf.drive1=0x378,0,36
+
+In the last option, pf.drive1 configures device /dev/pf1, the 0x378
+is the parallel port base address, the 0 is the protocol registration
+number and 36 is the chain ID.
+
+Please note: while PARIDE will work both with and without the
+PARPORT parallel port sharing system that is included by the
+"Parallel port support" option, PARPORT must be included and enabled
+if you want to use chains of devices on the same parallel port.
+
+2.2 Loading and configuring PARIDE as modules
+----------------------------------------------
+
+It is much faster and simpler to get to understand the PARIDE drivers
+if you use them as loadable kernel modules.
+
+Note 1:
+ using these drivers with the "kerneld" automatic module loading
+ system is not recommended for beginners, and is not documented here.
+
+Note 2:
+ if you build PARPORT support as a loadable module, PARIDE must
+ also be built as loadable modules, and PARPORT must be loaded before
+ the PARIDE modules.
+
+To use PARIDE, you must begin by::
+
+ insmod paride
+
+this loads a base module which provides a registry for the protocols,
+among other tasks.
+
+Then, load as many of the protocol modules as you think you might need.
+As you load each module, it will register the protocols that it supports,
+and print a log message to your kernel log file and your console. For
+example::
+
+ # insmod epat
+ paride: epat registered as protocol 0
+ # insmod kbic
+ paride: k951 registered as protocol 1
+ paride: k971 registered as protocol 2
+
+Finally, you can load high-level drivers for each kind of device that
+you have connected. By default, each driver will autoprobe for a single
+device, but you can support up to four similar devices by giving their
+individual coordinates when you load the driver.
+
+For example, if you had two no-name CD-ROM drives both using the
+KingByte KBIC-951A adapter, one on port 0x378 and the other on 0x3bc
+you could give the following command::
+
+ # insmod pcd drive0=0x378,1 drive1=0x3bc,1
+
+For most adapters, giving a port address and protocol number is sufficient,
+but check the source files in linux/drivers/block/paride for more
+information. (Hopefully someone will write some man pages one day !).
+
+As another example, here's what happens when PARPORT is installed, and
+a SyQuest EZ-135 is attached to port 0x378::
+
+ # insmod paride
+ paride: version 1.0 installed
+ # insmod epat
+ paride: epat registered as protocol 0
+ # insmod pd
+ pd: pd version 1.0, major 45, cluster 64, nice 0
+ pda: Sharing parport1 at 0x378
+ pda: epat 1.0, Shuttle EPAT chip c3 at 0x378, mode 5 (EPP-32), delay 1
+ pda: SyQuest EZ135A, 262144 blocks [128M], (512/16/32), removable media
+ pda: pda1
+
+Note that the last line is the output from the generic partition table
+scanner - in this case it reports that it has found a disk with one partition.
+
+2.3 Using a PARIDE device
+--------------------------
+
+Once the drivers have been loaded, you can access PARIDE devices in the
+same way as their traditional counterparts. You will probably need to
+create the device "special files". Here is a simple script that you can
+cut to a file and execute::
+
+ #!/bin/bash
+ #
+ # mkd -- a script to create the device special files for the PARIDE subsystem
+ #
+ function mkdev {
+ mknod $1 $2 $3 $4 ; chmod 0660 $1 ; chown root:disk $1
+ }
+ #
+ function pd {
+ D=$( printf \\$( printf "x%03x" $[ $1 + 97 ] ) )
+ mkdev pd$D b 45 $[ $1 * 16 ]
+ for P in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+ do mkdev pd$D$P b 45 $[ $1 * 16 + $P ]
+ done
+ }
+ #
+ cd /dev
+ #
+ for u in 0 1 2 3 ; do pd $u ; done
+ for u in 0 1 2 3 ; do mkdev pcd$u b 46 $u ; done
+ for u in 0 1 2 3 ; do mkdev pf$u b 47 $u ; done
+ for u in 0 1 2 3 ; do mkdev pt$u c 96 $u ; done
+ for u in 0 1 2 3 ; do mkdev npt$u c 96 $[ $u + 128 ] ; done
+ for u in 0 1 2 3 ; do mkdev pg$u c 97 $u ; done
+ #
+ # end of mkd
+
+With the device files and drivers in place, you can access PARIDE devices
+like any other Linux device. For example, to mount a CD-ROM in pcd0, use::
+
+ mount /dev/pcd0 /cdrom
+
+If you have a fresh Avatar Shark cartridge, and the drive is pda, you
+might do something like::
+
+ fdisk /dev/pda -- make a new partition table with
+ partition 1 of type 83
+
+ mke2fs /dev/pda1 -- to build the file system
+
+ mkdir /shark -- make a place to mount the disk
+
+ mount /dev/pda1 /shark
+
+Devices like the Imation superdisk work in the same way, except that
+they do not have a partition table. For example to make a 120MB
+floppy that you could share with a DOS system::
+
+ mkdosfs /dev/pf0
+ mount /dev/pf0 /mnt
+
+
+2.4 The pf driver
+------------------
+
+The pf driver is intended for use with parallel port ATAPI disk
+devices. The most common devices in this category are PD drives
+and LS-120 drives. Traditionally, media for these devices are not
+partitioned. Consequently, the pf driver does not support partitioned
+media. This may be changed in a future version of the driver.
+
+2.5 Using the pt driver
+------------------------
+
+The pt driver for parallel port ATAPI tape drives is a minimal driver.
+It does not yet support many of the standard tape ioctl operations.
+For best performance, a block size of 32KB should be used. You will
+probably want to set the parallel port delay to 0, if you can.
+
+2.6 Using the pg driver
+------------------------
+
+The pg driver can be used in conjunction with the cdrecord program
+to create CD-ROMs. Please get cdrecord version 1.6.1 or later
+from ftp://ftp.fokus.gmd.de/pub/unix/cdrecord/ . To record CD-R media
+your parallel port should ideally be set to EPP mode, and the "port delay"
+should be set to 0. With those settings it is possible to record at 2x
+speed without any buffer underruns. If you cannot get the driver to work
+in EPP mode, try to use "bidirectional" or "PS/2" mode and 1x speeds only.
+
+
+3. Troubleshooting
+==================
+
+3.1 Use EPP mode if you can
+----------------------------
+
+The most common problems that people report with the PARIDE drivers
+concern the parallel port CMOS settings. At this time, none of the
+PARIDE protocol modules support ECP mode, or any ECP combination modes.
+If you are able to do so, please set your parallel port into EPP mode
+using your CMOS setup procedure.
+
+3.2 Check the port delay
+-------------------------
+
+Some parallel ports cannot reliably transfer data at full speed. To
+offset the errors, the PARIDE protocol modules introduce a "port
+delay" between each access to the i/o ports. Each protocol sets
+a default value for this delay. In most cases, the user can override
+the default and set it to 0 - resulting in somewhat higher transfer
+rates. In some rare cases (especially with older 486 systems) the
+default delays are not long enough. if you experience corrupt data
+transfers, or unexpected failures, you may wish to increase the
+port delay. The delay can be programmed using the "driveN" parameters
+to each of the high-level drivers. Please see the notes above, or
+read the comments at the beginning of the driver source files in
+linux/drivers/block/paride.
+
+3.3 Some drives need a printer reset
+-------------------------------------
+
+There appear to be a number of "noname" external drives on the market
+that do not always power up correctly. We have noticed this with some
+drives based on OnSpec and older Freecom adapters. In these rare cases,
+the adapter can often be reinitialised by issuing a "printer reset" on
+the parallel port. As the reset operation is potentially disruptive in
+multiple device environments, the PARIDE drivers will not do it
+automatically. You can however, force a printer reset by doing::
+
+ insmod lp reset=1
+ rmmod lp
+
+If you have one of these marginal cases, you should probably build
+your paride drivers as modules, and arrange to do the printer reset
+before loading the PARIDE drivers.
+
+3.4 Use the verbose option and dmesg if you need help
+------------------------------------------------------
+
+While a lot of testing has gone into these drivers to make them work
+as smoothly as possible, problems will arise. If you do have problems,
+please check all the obvious things first: does the drive work in
+DOS with the manufacturer's drivers ? If that doesn't yield any useful
+clues, then please make sure that only one drive is hooked to your system,
+and that either (a) PARPORT is enabled or (b) no other device driver
+is using your parallel port (check in /proc/ioports). Then, load the
+appropriate drivers (you can load several protocol modules if you want)
+as in::
+
+ # insmod paride
+ # insmod epat
+ # insmod bpck
+ # insmod kbic
+ ...
+ # insmod pd verbose=1
+
+(using the correct driver for the type of device you have, of course).
+The verbose=1 parameter will cause the drivers to log a trace of their
+activity as they attempt to locate your drive.
+
+Use 'dmesg' to capture a log of all the PARIDE messages (any messages
+beginning with paride:, a protocol module's name or a driver's name) and
+include that with your bug report. You can submit a bug report in one
+of two ways. Either send it directly to the author of the PARIDE suite,
+by e-mail to grant@torque.net, or join the linux-parport mailing list
+and post your report there.
+
+3.5 For more information or help
+---------------------------------
+
+You can join the linux-parport mailing list by sending a mail message
+to:
+
+ linux-parport-request@torque.net
+
+with the single word::
+
+ subscribe
+
+in the body of the mail message (not in the subject line). Please be
+sure that your mail program is correctly set up when you do this, as
+the list manager is a robot that will subscribe you using the reply
+address in your mail headers. REMOVE any anti-spam gimmicks you may
+have in your mail headers, when sending mail to the list server.
+
+You might also find some useful information on the linux-parport
+web pages (although they are not always up to date) at
+
+ http://web.archive.org/web/%2E/http://www.torque.net/parport/
diff --git a/Documentation/admin-guide/blockdev/ramdisk.rst b/Documentation/admin-guide/blockdev/ramdisk.rst
new file mode 100644
index 000000000..9ce6101e8
--- /dev/null
+++ b/Documentation/admin-guide/blockdev/ramdisk.rst
@@ -0,0 +1,153 @@
+==========================================
+Using the RAM disk block device with Linux
+==========================================
+
+.. Contents:
+
+ 1) Overview
+ 2) Kernel Command Line Parameters
+ 3) Using "rdev"
+ 4) An Example of Creating a Compressed RAM Disk
+
+
+1) Overview
+-----------
+
+The RAM disk driver is a way to use main system memory as a block device. It
+is required for initrd, an initial filesystem used if you need to load modules
+in order to access the root filesystem (see Documentation/admin-guide/initrd.rst). It can
+also be used for a temporary filesystem for crypto work, since the contents
+are erased on reboot.
+
+The RAM disk dynamically grows as more space is required. It does this by using
+RAM from the buffer cache. The driver marks the buffers it is using as dirty
+so that the VM subsystem does not try to reclaim them later.
+
+The RAM disk supports up to 16 RAM disks by default, and can be reconfigured
+to support an unlimited number of RAM disks (at your own risk). Just change
+the configuration symbol BLK_DEV_RAM_COUNT in the Block drivers config menu
+and (re)build the kernel.
+
+To use RAM disk support with your system, run './MAKEDEV ram' from the /dev
+directory. RAM disks are all major number 1, and start with minor number 0
+for /dev/ram0, etc. If used, modern kernels use /dev/ram0 for an initrd.
+
+The new RAM disk also has the ability to load compressed RAM disk images,
+allowing one to squeeze more programs onto an average installation or
+rescue floppy disk.
+
+
+2) Parameters
+---------------------------------
+
+2a) Kernel Command Line Parameters
+
+ ramdisk_size=N
+ Size of the ramdisk.
+
+This parameter tells the RAM disk driver to set up RAM disks of N k size. The
+default is 4096 (4 MB).
+
+2b) Module parameters
+
+ rd_nr
+ /dev/ramX devices created.
+
+ max_part
+ Maximum partition number.
+
+ rd_size
+ See ramdisk_size.
+
+3) Using "rdev"
+---------------
+
+"rdev" is an obsolete, deprecated, antiquated utility that could be used
+to set the boot device in a Linux kernel image.
+
+Instead of using rdev, just place the boot device information on the
+kernel command line and pass it to the kernel from the bootloader.
+
+You can also pass arguments to the kernel by setting FDARGS in
+arch/x86/boot/Makefile and specify in initrd image by setting FDINITRD in
+arch/x86/boot/Makefile.
+
+Some of the kernel command line boot options that may apply here are::
+
+ ramdisk_start=N
+ ramdisk_size=M
+
+If you make a boot disk that has LILO, then for the above, you would use::
+
+ append = "ramdisk_start=N ramdisk_size=M"
+
+4) An Example of Creating a Compressed RAM Disk
+-----------------------------------------------
+
+To create a RAM disk image, you will need a spare block device to
+construct it on. This can be the RAM disk device itself, or an
+unused disk partition (such as an unmounted swap partition). For this
+example, we will use the RAM disk device, "/dev/ram0".
+
+Note: This technique should not be done on a machine with less than 8 MB
+of RAM. If using a spare disk partition instead of /dev/ram0, then this
+restriction does not apply.
+
+a) Decide on the RAM disk size that you want. Say 2 MB for this example.
+ Create it by writing to the RAM disk device. (This step is not currently
+ required, but may be in the future.) It is wise to zero out the
+ area (esp. for disks) so that maximal compression is achieved for
+ the unused blocks of the image that you are about to create::
+
+ dd if=/dev/zero of=/dev/ram0 bs=1k count=2048
+
+b) Make a filesystem on it. Say ext2fs for this example::
+
+ mke2fs -vm0 /dev/ram0 2048
+
+c) Mount it, copy the files you want to it (eg: /etc/* /dev/* ...)
+ and unmount it again.
+
+d) Compress the contents of the RAM disk. The level of compression
+ will be approximately 50% of the space used by the files. Unused
+ space on the RAM disk will compress to almost nothing::
+
+ dd if=/dev/ram0 bs=1k count=2048 | gzip -v9 > /tmp/ram_image.gz
+
+e) Put the kernel onto the floppy::
+
+ dd if=zImage of=/dev/fd0 bs=1k
+
+f) Put the RAM disk image onto the floppy, after the kernel. Use an offset
+ that is slightly larger than the kernel, so that you can put another
+ (possibly larger) kernel onto the same floppy later without overlapping
+ the RAM disk image. An offset of 400 kB for kernels about 350 kB in
+ size would be reasonable. Make sure offset+size of ram_image.gz is
+ not larger than the total space on your floppy (usually 1440 kB)::
+
+ dd if=/tmp/ram_image.gz of=/dev/fd0 bs=1k seek=400
+
+g) Make sure that you have already specified the boot information in
+ FDARGS and FDINITRD or that you use a bootloader to pass kernel
+ command line boot options to the kernel.
+
+That is it. You now have your boot/root compressed RAM disk floppy. Some
+users may wish to combine steps (d) and (f) by using a pipe.
+
+
+ Paul Gortmaker 12/95
+
+Changelog:
+----------
+
+SEPT-2020 :
+
+ Removed usage of "rdev"
+
+10-22-04 :
+ Updated to reflect changes in command line options, remove
+ obsolete references, general cleanup.
+ James Nelson (james4765@gmail.com)
+
+12-95 :
+ Original Document
diff --git a/Documentation/admin-guide/blockdev/zram.rst b/Documentation/admin-guide/blockdev/zram.rst
new file mode 100644
index 000000000..c73b16930
--- /dev/null
+++ b/Documentation/admin-guide/blockdev/zram.rst
@@ -0,0 +1,440 @@
+========================================
+zram: Compressed RAM-based block devices
+========================================
+
+Introduction
+============
+
+The zram module creates RAM-based block devices named /dev/zram<id>
+(<id> = 0, 1, ...). Pages written to these disks are compressed and stored
+in memory itself. These disks allow very fast I/O and compression provides
+good amounts of memory savings. Some of the use cases include /tmp storage,
+use as swap disks, various caches under /var and maybe many more. :)
+
+Statistics for individual zram devices are exported through sysfs nodes at
+/sys/block/zram<id>/
+
+Usage
+=====
+
+There are several ways to configure and manage zram device(-s):
+
+a) using zram and zram_control sysfs attributes
+b) using zramctl utility, provided by util-linux (util-linux@vger.kernel.org).
+
+In this document we will describe only 'manual' zram configuration steps,
+IOW, zram and zram_control sysfs attributes.
+
+In order to get a better idea about zramctl please consult util-linux
+documentation, zramctl man-page or `zramctl --help`. Please be informed
+that zram maintainers do not develop/maintain util-linux or zramctl, should
+you have any questions please contact util-linux@vger.kernel.org
+
+Following shows a typical sequence of steps for using zram.
+
+WARNING
+=======
+
+For the sake of simplicity we skip error checking parts in most of the
+examples below. However, it is your sole responsibility to handle errors.
+
+zram sysfs attributes always return negative values in case of errors.
+The list of possible return codes:
+
+======== =============================================================
+-EBUSY an attempt to modify an attribute that cannot be changed once
+ the device has been initialised. Please reset device first.
+-ENOMEM zram was not able to allocate enough memory to fulfil your
+ needs.
+-EINVAL invalid input has been provided.
+======== =============================================================
+
+If you use 'echo', the returned value is set by the 'echo' utility,
+and, in general case, something like::
+
+ echo 3 > /sys/block/zram0/max_comp_streams
+ if [ $? -ne 0 ]; then
+ handle_error
+ fi
+
+should suffice.
+
+1) Load Module
+==============
+
+::
+
+ modprobe zram num_devices=4
+
+This creates 4 devices: /dev/zram{0,1,2,3}
+
+num_devices parameter is optional and tells zram how many devices should be
+pre-created. Default: 1.
+
+2) Set max number of compression streams
+========================================
+
+Regardless of the value passed to this attribute, ZRAM will always
+allocate multiple compression streams - one per online CPU - thus
+allowing several concurrent compression operations. The number of
+allocated compression streams goes down when some of the CPUs
+become offline. There is no single-compression-stream mode anymore,
+unless you are running a UP system or have only 1 CPU online.
+
+To find out how many streams are currently available::
+
+ cat /sys/block/zram0/max_comp_streams
+
+3) Select compression algorithm
+===============================
+
+Using comp_algorithm device attribute one can see available and
+currently selected (shown in square brackets) compression algorithms,
+or change the selected compression algorithm (once the device is initialised
+there is no way to change compression algorithm).
+
+Examples::
+
+ #show supported compression algorithms
+ cat /sys/block/zram0/comp_algorithm
+ lzo [lz4]
+
+ #select lzo compression algorithm
+ echo lzo > /sys/block/zram0/comp_algorithm
+
+For the time being, the `comp_algorithm` content does not necessarily
+show every compression algorithm supported by the kernel. We keep this
+list primarily to simplify device configuration and one can configure
+a new device with a compression algorithm that is not listed in
+`comp_algorithm`. The thing is that, internally, ZRAM uses Crypto API
+and, if some of the algorithms were built as modules, it's impossible
+to list all of them using, for instance, /proc/crypto or any other
+method. This, however, has an advantage of permitting the usage of
+custom crypto compression modules (implementing S/W or H/W compression).
+
+4) Set Disksize
+===============
+
+Set disk size by writing the value to sysfs node 'disksize'.
+The value can be either in bytes or you can use mem suffixes.
+Examples::
+
+ # Initialize /dev/zram0 with 50MB disksize
+ echo $((50*1024*1024)) > /sys/block/zram0/disksize
+
+ # Using mem suffixes
+ echo 256K > /sys/block/zram0/disksize
+ echo 512M > /sys/block/zram0/disksize
+ echo 1G > /sys/block/zram0/disksize
+
+Note:
+There is little point creating a zram of greater than twice the size of memory
+since we expect a 2:1 compression ratio. Note that zram uses about 0.1% of the
+size of the disk when not in use so a huge zram is wasteful.
+
+5) Set memory limit: Optional
+=============================
+
+Set memory limit by writing the value to sysfs node 'mem_limit'.
+The value can be either in bytes or you can use mem suffixes.
+In addition, you could change the value in runtime.
+Examples::
+
+ # limit /dev/zram0 with 50MB memory
+ echo $((50*1024*1024)) > /sys/block/zram0/mem_limit
+
+ # Using mem suffixes
+ echo 256K > /sys/block/zram0/mem_limit
+ echo 512M > /sys/block/zram0/mem_limit
+ echo 1G > /sys/block/zram0/mem_limit
+
+ # To disable memory limit
+ echo 0 > /sys/block/zram0/mem_limit
+
+6) Activate
+===========
+
+::
+
+ mkswap /dev/zram0
+ swapon /dev/zram0
+
+ mkfs.ext4 /dev/zram1
+ mount /dev/zram1 /tmp
+
+7) Add/remove zram devices
+==========================
+
+zram provides a control interface, which enables dynamic (on-demand) device
+addition and removal.
+
+In order to add a new /dev/zramX device, perform a read operation on the hot_add
+attribute. This will return either the new device's device id (meaning that you
+can use /dev/zram<id>) or an error code.
+
+Example::
+
+ cat /sys/class/zram-control/hot_add
+ 1
+
+To remove the existing /dev/zramX device (where X is a device id)
+execute::
+
+ echo X > /sys/class/zram-control/hot_remove
+
+8) Stats
+========
+
+Per-device statistics are exported as various nodes under /sys/block/zram<id>/
+
+A brief description of exported device attributes follows. For more details
+please read Documentation/ABI/testing/sysfs-block-zram.
+
+====================== ====== ===============================================
+Name access description
+====================== ====== ===============================================
+disksize RW show and set the device's disk size
+initstate RO shows the initialization state of the device
+reset WO trigger device reset
+mem_used_max WO reset the `mem_used_max` counter (see later)
+mem_limit WO specifies the maximum amount of memory ZRAM can
+ use to store the compressed data
+writeback_limit WO specifies the maximum amount of write IO zram
+ can write out to backing device as 4KB unit
+writeback_limit_enable RW show and set writeback_limit feature
+max_comp_streams RW the number of possible concurrent compress
+ operations
+comp_algorithm RW show and change the compression algorithm
+compact WO trigger memory compaction
+debug_stat RO this file is used for zram debugging purposes
+backing_dev RW set up backend storage for zram to write out
+idle WO mark allocated slot as idle
+====================== ====== ===============================================
+
+
+User space is advised to use the following files to read the device statistics.
+
+File /sys/block/zram<id>/stat
+
+Represents block layer statistics. Read Documentation/block/stat.rst for
+details.
+
+File /sys/block/zram<id>/io_stat
+
+The stat file represents device's I/O statistics not accounted by block
+layer and, thus, not available in zram<id>/stat file. It consists of a
+single line of text and contains the following stats separated by
+whitespace:
+
+ ============= =============================================================
+ failed_reads The number of failed reads
+ failed_writes The number of failed writes
+ invalid_io The number of non-page-size-aligned I/O requests
+ notify_free Depending on device usage scenario it may account
+
+ a) the number of pages freed because of swap slot free
+ notifications
+ b) the number of pages freed because of
+ REQ_OP_DISCARD requests sent by bio. The former ones are
+ sent to a swap block device when a swap slot is freed,
+ which implies that this disk is being used as a swap disk.
+
+ The latter ones are sent by filesystem mounted with
+ discard option, whenever some data blocks are getting
+ discarded.
+ ============= =============================================================
+
+File /sys/block/zram<id>/mm_stat
+
+The mm_stat file represents the device's mm statistics. It consists of a single
+line of text and contains the following stats separated by whitespace:
+
+ ================ =============================================================
+ orig_data_size uncompressed size of data stored in this disk.
+ Unit: bytes
+ compr_data_size compressed size of data stored in this disk
+ mem_used_total the amount of memory allocated for this disk. This
+ includes allocator fragmentation and metadata overhead,
+ allocated for this disk. So, allocator space efficiency
+ can be calculated using compr_data_size and this statistic.
+ Unit: bytes
+ mem_limit the maximum amount of memory ZRAM can use to store
+ the compressed data
+ mem_used_max the maximum amount of memory zram has consumed to
+ store the data
+ same_pages the number of same element filled pages written to this disk.
+ No memory is allocated for such pages.
+ pages_compacted the number of pages freed during compaction
+ huge_pages the number of incompressible pages
+ huge_pages_since the number of incompressible pages since zram set up
+ ================ =============================================================
+
+File /sys/block/zram<id>/bd_stat
+
+The bd_stat file represents a device's backing device statistics. It consists of
+a single line of text and contains the following stats separated by whitespace:
+
+ ============== =============================================================
+ bd_count size of data written in backing device.
+ Unit: 4K bytes
+ bd_reads the number of reads from backing device
+ Unit: 4K bytes
+ bd_writes the number of writes to backing device
+ Unit: 4K bytes
+ ============== =============================================================
+
+9) Deactivate
+=============
+
+::
+
+ swapoff /dev/zram0
+ umount /dev/zram1
+
+10) Reset
+=========
+
+ Write any positive value to 'reset' sysfs node::
+
+ echo 1 > /sys/block/zram0/reset
+ echo 1 > /sys/block/zram1/reset
+
+ This frees all the memory allocated for the given device and
+ resets the disksize to zero. You must set the disksize again
+ before reusing the device.
+
+Optional Feature
+================
+
+writeback
+---------
+
+With CONFIG_ZRAM_WRITEBACK, zram can write idle/incompressible page
+to backing storage rather than keeping it in memory.
+To use the feature, admin should set up backing device via::
+
+ echo /dev/sda5 > /sys/block/zramX/backing_dev
+
+before disksize setting. It supports only partitions at this moment.
+If admin wants to use incompressible page writeback, they could do it via::
+
+ echo huge > /sys/block/zramX/writeback
+
+To use idle page writeback, first, user need to declare zram pages
+as idle::
+
+ echo all > /sys/block/zramX/idle
+
+From now on, any pages on zram are idle pages. The idle mark
+will be removed until someone requests access of the block.
+IOW, unless there is access request, those pages are still idle pages.
+Additionally, when CONFIG_ZRAM_MEMORY_TRACKING is enabled pages can be
+marked as idle based on how long (in seconds) it's been since they were
+last accessed::
+
+ echo 86400 > /sys/block/zramX/idle
+
+In this example all pages which haven't been accessed in more than 86400
+seconds (one day) will be marked idle.
+
+Admin can request writeback of those idle pages at right timing via::
+
+ echo idle > /sys/block/zramX/writeback
+
+With the command, zram will writeback idle pages from memory to the storage.
+
+Additionally, if a user choose to writeback only huge and idle pages
+this can be accomplished with::
+
+ echo huge_idle > /sys/block/zramX/writeback
+
+If an admin wants to write a specific page in zram device to the backing device,
+they could write a page index into the interface.
+
+ echo "page_index=1251" > /sys/block/zramX/writeback
+
+If there are lots of write IO with flash device, potentially, it has
+flash wearout problem so that admin needs to design write limitation
+to guarantee storage health for entire product life.
+
+To overcome the concern, zram supports "writeback_limit" feature.
+The "writeback_limit_enable"'s default value is 0 so that it doesn't limit
+any writeback. IOW, if admin wants to apply writeback budget, they should
+enable writeback_limit_enable via::
+
+ $ echo 1 > /sys/block/zramX/writeback_limit_enable
+
+Once writeback_limit_enable is set, zram doesn't allow any writeback
+until admin sets the budget via /sys/block/zramX/writeback_limit.
+
+(If admin doesn't enable writeback_limit_enable, writeback_limit's value
+assigned via /sys/block/zramX/writeback_limit is meaningless.)
+
+If admin wants to limit writeback as per-day 400M, they could do it
+like below::
+
+ $ MB_SHIFT=20
+ $ 4K_SHIFT=12
+ $ echo $((400<<MB_SHIFT>>4K_SHIFT)) > \
+ /sys/block/zram0/writeback_limit.
+ $ echo 1 > /sys/block/zram0/writeback_limit_enable
+
+If admins want to allow further write again once the budget is exhausted,
+they could do it like below::
+
+ $ echo $((400<<MB_SHIFT>>4K_SHIFT)) > \
+ /sys/block/zram0/writeback_limit
+
+If an admin wants to see the remaining writeback budget since last set::
+
+ $ cat /sys/block/zramX/writeback_limit
+
+If an admin wants to disable writeback limit, they could do::
+
+ $ echo 0 > /sys/block/zramX/writeback_limit_enable
+
+The writeback_limit count will reset whenever you reset zram (e.g.,
+system reboot, echo 1 > /sys/block/zramX/reset) so keeping how many of
+writeback happened until you reset the zram to allocate extra writeback
+budget in next setting is user's job.
+
+If admin wants to measure writeback count in a certain period, they could
+know it via /sys/block/zram0/bd_stat's 3rd column.
+
+memory tracking
+===============
+
+With CONFIG_ZRAM_MEMORY_TRACKING, user can know information of the
+zram block. It could be useful to catch cold or incompressible
+pages of the process with*pagemap.
+
+If you enable the feature, you could see block state via
+/sys/kernel/debug/zram/zram0/block_state". The output is as follows::
+
+ 300 75.033841 .wh.
+ 301 63.806904 s...
+ 302 63.806919 ..hi
+
+First column
+ zram's block index.
+Second column
+ access time since the system was booted
+Third column
+ state of the block:
+
+ s:
+ same page
+ w:
+ written page to backing store
+ h:
+ huge page
+ i:
+ idle page
+
+First line of above example says 300th block is accessed at 75.033841sec
+and the block's state is huge so it is written back to the backing
+storage. It's a debugging feature so anyone shouldn't rely on it to work
+properly.
+
+Nitin Gupta
+ngupta@vflare.org