1kcopyd
2======
3
4Kcopyd provides the ability to copy a range of sectors from one block-device
5to one or more other block-devices, with an asynchronous completion
6notification. It is used by dm-snapshot and dm-mirror.
7
8Users of kcopyd must first create a client and indicate how many memory pages
9to set aside for their copy jobs. This is done with a call to
10kcopyd_client_create().
11
12   int kcopyd_client_create(unsigned int num_pages,
13                            struct kcopyd_client **result);
14
15To start a copy job, the user must set up io_region structures to describe
16the source and destinations of the copy. Each io_region indicates a
17block-device along with the starting sector and size of the region. The source
18of the copy is given as one io_region structure, and the destinations of the
19copy are given as an array of io_region structures.
20
21   struct io_region {
22      struct block_device *bdev;
23      sector_t sector;
24      sector_t count;
25   };
26
27To start the copy, the user calls kcopyd_copy(), passing in the client
28pointer, pointers to the source and destination io_regions, the name of a
29completion callback routine, and a pointer to some context data for the copy.
30
31   int kcopyd_copy(struct kcopyd_client *kc, struct io_region *from,
32                   unsigned int num_dests, struct io_region *dests,
33                   unsigned int flags, kcopyd_notify_fn fn, void *context);
34
35   typedef void (*kcopyd_notify_fn)(int read_err, unsigned int write_err,
36				    void *context);
37
38When the copy completes, kcopyd will call the user's completion routine,
39passing back the user's context pointer. It will also indicate if a read or
40write error occurred during the copy.
41
42When a user is done with all their copy jobs, they should call
43kcopyd_client_destroy() to delete the kcopyd client, which will release the
44associated memory pages.
45
46   void kcopyd_client_destroy(struct kcopyd_client *kc);
47
48