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Old 05-15-2008, 09:16 AM
Nikanth Karthikesan
 
Default Documentation: change dm-io.txt to document the new ap

Change documentation in dm-io.txt to the new API

Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>

--
Documentation/device-mapper/dm-io.txt | 87 ++++++++++++++++++++++-----------
1 files changed, 58 insertions(+), 29 deletions(-)

diff --git a/Documentation/device-mapper/dm-io.txt b/Documentation/device-mapper/dm-io.txt
index 3b5d9a5..52ebff3 100644
--- a/Documentation/device-mapper/dm-io.txt
+++ b/Documentation/device-mapper/dm-io.txt
@@ -26,50 +26,79 @@ the I/O, along with an offset into the f
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);
+The fourth I/O service type takes a pointer to kernel memory as the data
+buffer for I/O.
+
+To use any of the I/O service callers should setup a dm_io_request and
+submit it using dm_io().
+
+ struct dm_io_request {
+ int bi_rw; /* READ|WRITE - not READA */
+ struct dm_io_memory mem; /* Memory to use for io */
+ struct dm_io_notify notify; /* Synchronous if notify.fn is NULL */
+ struct dm_io_client *client; /* Client memory handler */
+ };
+
+ int dm_io(struct dm_io_request *io_req, unsigned num_regions,
+ struct io_region *region, unsigned long *sync_error_bits);
+
+The type of I/O service is chosen by specifying the appropriate dm_io_mem_type
+and populating the corresponding pointer in dm_io_memory.
+
+ struct dm_io_memory {
+ enum dm_io_mem_type type;
+
+ union {
+ struct page_list *pl;
+ struct bio_vec *bvec;
+ void *vma;
+ void *addr;
+ } ptr;
+
+ unsigned offset;
+ };
+
+ enum dm_io_mem_type {
+ DM_IO_PAGE_LIST,/* Page list */
+ DM_IO_BVEC, /* Bio vector */
+ DM_IO_VMA, /* Virtual memory area */
+ DM_IO_KMEM, /* Kernel memory */
+ };
+

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.
+ struct dm_io_notify {
+ io_notify_fn fn; /* Callback for asynchronous requests */
+ void *context; /* Passed to callback */
+ };
+
+
+For asynchronous I/O, private mempools should be created using
+dm_io_client_create().
+
+ struct dm_io_client *dm_io_client_create(unsigned num_pages);
+
+dm_io_client_resize() is used to resize the mempool of the client. To free the
+mempool dm_io_client_destroy() should be used.

-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.
+ int dm_io_client_resize(unsigned num_pages, struct dm_io_client *client);
+ void dm_io_client_destroy(struct dm_io_client *client);

-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.
+The "error" parameter in this callback, as well as the sync_error_bits
+parameter in dm_io for synchronous calls 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.



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