docs: convert docs to ReST and rename to *.rst

[linux-2.6-microblaze.git] / Documentation / device-mapper / dm-io.txt

diff --git a/Documentation/device-mapper/dm-io.txt b/Documentation/device-mapper/dm-io.txt
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-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.
-