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