1 ======
2 kcopyd
3 ======
4
5 Kcopyd provides the ability to copy a range of sectors from one block-device
6 to one or more other block-devices, with an asynchronous completion
7 notification. It is used by dm-snapshot and dm-mirror.
8
9 Users of kcopyd must first create a client and indicate how many memory pages
10 to set aside for their copy jobs. This is done with a call to
11 kcopyd_client_create()::
12
13 int kcopyd_client_create(unsigned int num_pages,
14 struct kcopyd_client **result);
15
16 To start a copy job, the user must set up io_region structures to describe
17 the source and destinations of the copy. Each io_region indicates a
18 block-device along with the starting sector and size of the region. The source
19 of the copy is given as one io_region structure, and the destinations of the
20 copy are given as an array of io_region structures::
21
22 struct io_region {
23 struct block_device *bdev;
24 sector_t sector;
25 sector_t count;
26 };
27
28 To start the copy, the user calls kcopyd_copy(), passing in the client
29 pointer, pointers to the source and destination io_regions, the name of a
30 completion callback routine, and a pointer to some context data for the copy::
31
32 int kcopyd_copy(struct kcopyd_client *kc, struct io_region *from,
33 unsigned int num_dests, struct io_region *dests,
34 unsigned int flags, kcopyd_notify_fn fn, void *context);
35
36 typedef void (*kcopyd_notify_fn)(int read_err, unsigned int write_err,
37 void *context);
38
39 When the copy completes, kcopyd will call the user's completion routine,
40 passing back the user's context pointer. It will also indicate if a read or
41 write error occurred during the copy.
42
43 When a user is done with all their copy jobs, they should call
44 kcopyd_client_destroy() to delete the kcopyd client, which will release the
45 associated memory pages::
46
47 void kcopyd_client_destroy(struct kcopyd_client *kc);
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