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authorMauro Carvalho Chehab <mchehab+samsung@kernel.org>2019-06-12 20:52:43 +0300
committerJonathan Corbet <corbet@lwn.net>2019-06-14 23:21:04 +0300
commitf0ba43774cea3fc14732bb9243ce7238ae8a3202 (patch)
tree5579b300bfc410ed14bb3112586cef02750d7eb0 /Documentation/device-mapper/dm-io.txt
parent8ea618899b6b4fbe97c8462e7d769867307de011 (diff)
downloadlinux-f0ba43774cea3fc14732bb9243ce7238ae8a3202.tar.xz
docs: convert docs to ReST and rename to *.rst
The conversion is actually: - add blank lines and indentation in order to identify paragraphs; - fix tables markups; - add some lists markups; - mark literal blocks; - adjust title markups. At its new index.rst, let's add a :orphan: while this is not linked to the main index.rst file, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Acked-by: Bjorn Helgaas <bhelgaas@google.com> Acked-by: Mark Brown <broonie@kernel.org> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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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.
-