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