diff options
author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
---|---|---|
committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/admin-guide/device-mapper/dm-io.rst | |
parent | Initial commit. (diff) | |
download | linux-upstream/5.10.209.tar.xz linux-upstream/5.10.209.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | Documentation/admin-guide/device-mapper/dm-io.rst | 75 |
1 files changed, 75 insertions, 0 deletions
diff --git a/Documentation/admin-guide/device-mapper/dm-io.rst b/Documentation/admin-guide/device-mapper/dm-io.rst new file mode 100644 index 000000000..d2492917a --- /dev/null +++ b/Documentation/admin-guide/device-mapper/dm-io.rst @@ -0,0 +1,75 @@ +===== +dm-io +===== + +Dm-io provides synchronous and asynchronous I/O services. There are three +types of I/O services available, and each type has a sync and an async +version. + +The user must set up an io_region structure to describe the desired location +of the I/O. Each io_region indicates a block-device along with the starting +sector and size of the region:: + + struct io_region { + struct block_device *bdev; + sector_t sector; + sector_t count; + }; + +Dm-io can read from one io_region or write to one or more io_regions. Writes +to multiple regions are specified by an array of io_region structures. + +The first I/O service type takes a list of memory pages as the data buffer for +the I/O, along with an offset into the first page:: + + struct page_list { + struct page_list *next; + struct page *page; + }; + + int dm_io_sync(unsigned int num_regions, struct io_region *where, int rw, + struct page_list *pl, unsigned int offset, + unsigned long *error_bits); + int dm_io_async(unsigned int num_regions, struct io_region *where, int rw, + struct page_list *pl, unsigned int offset, + io_notify_fn fn, void *context); + +The second I/O service type takes an array of bio vectors as the data buffer +for the I/O. This service can be handy if the caller has a pre-assembled bio, +but wants to direct different portions of the bio to different devices:: + + int dm_io_sync_bvec(unsigned int num_regions, struct io_region *where, + int rw, struct bio_vec *bvec, + unsigned long *error_bits); + int dm_io_async_bvec(unsigned int num_regions, struct io_region *where, + int rw, struct bio_vec *bvec, + io_notify_fn fn, void *context); + +The third I/O service type takes a pointer to a vmalloc'd memory buffer as the +data buffer for the I/O. This service can be handy if the caller needs to do +I/O to a large region but doesn't want to allocate a large number of individual +memory pages:: + + int dm_io_sync_vm(unsigned int num_regions, struct io_region *where, int rw, + void *data, unsigned long *error_bits); + int dm_io_async_vm(unsigned int num_regions, struct io_region *where, int rw, + void *data, io_notify_fn fn, void *context); + +Callers of the asynchronous I/O services must include the name of a completion +callback routine and a pointer to some context data for the I/O:: + + typedef void (*io_notify_fn)(unsigned long error, void *context); + +The "error" parameter in this callback, as well as the `*error` parameter in +all of the synchronous versions, is a bitset (instead of a simple error value). +In the case of an write-I/O to multiple regions, this bitset allows dm-io to +indicate success or failure on each individual region. + +Before using any of the dm-io services, the user should call dm_io_get() +and specify the number of pages they expect to perform I/O on concurrently. +Dm-io will attempt to resize its mempool to make sure enough pages are +always available in order to avoid unnecessary waiting while performing I/O. + +When the user is finished using the dm-io services, they should call +dm_io_put() and specify the same number of pages that were given on the +dm_io_get() call. |