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