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Documentation / device-mapper / kcopyd.txt




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Based on kernel version 3.16. Page generated on 2014-08-06 21:36 EST.

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