1 =====
2 dm-io
3 =====
4
5 Dm-io provides synchronous and asynchronous I/
6 types of I/O services available, and each type
7 version.
8
9 The user must set up an io_region structure to
10 of the I/O. Each io_region indicates a block-d
11 sector and size of the region::
12
13 struct io_region {
14 struct block_device *bdev;
15 sector_t sector;
16 sector_t count;
17 };
18
19 Dm-io can read from one io_region or write to
20 to multiple regions are specified by an array
21
22 The first I/O service type takes a list of mem
23 the I/O, along with an offset into the first p
24
25 struct page_list {
26 struct page_list *next;
27 struct page *page;
28 };
29
30 int dm_io_sync(unsigned int num_regions, st
31 struct page_list *pl, unsign
32 unsigned long *error_bits);
33 int dm_io_async(unsigned int num_regions, s
34 struct page_list *pl, unsig
35 io_notify_fn fn, void *cont
36
37 The second I/O service type takes an array of
38 for the I/O. This service can be handy if the
39 but wants to direct different portions of the
40
41 int dm_io_sync_bvec(unsigned int num_region
42 int rw, struct bio_vec
43 unsigned long *error_bi
44 int dm_io_async_bvec(unsigned int num_regio
45 int rw, struct bio_vec
46 io_notify_fn fn, void
47
48 The third I/O service type takes a pointer to
49 data buffer for the I/O. This service can be h
50 I/O to a large region but doesn't want to allo
51 memory pages::
52
53 int dm_io_sync_vm(unsigned int num_regions,
54 void *data, unsigned long
55 int dm_io_async_vm(unsigned int num_regions
56 void *data, io_notify_fn
57
58 Callers of the asynchronous I/O services must
59 callback routine and a pointer to some context
60
61 typedef void (*io_notify_fn)(unsigned long
62
63 The "error" parameter in this callback, as wel
64 all of the synchronous versions, is a bitset (
65 In the case of an write-I/O to multiple region
66 indicate success or failure on each individual
67
68 Before using any of the dm-io services, the us
69 and specify the number of pages they expect to
70 Dm-io will attempt to resize its mempool to ma
71 always available in order to avoid unnecessary
72
73 When the user is finished using the dm-io serv
74 dm_io_put() and specify the same number of pag
75 dm_io_get() call.
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