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-Kcopyd provides the ability to copy a range of sectors from one block-device
-to one or more other block-devices, with an asynchronous completion
-notification. It is used by dm-snapshot and dm-mirror.
-Users of kcopyd must first create a client and indicate how many memory pages
-to set aside for their copy jobs. This is done with a call to
- int kcopyd_client_create(unsigned int num_pages,
- struct kcopyd_client **result);
-To start a copy job, the user must set up io_region structures to describe
-the source and destinations of the copy. Each io_region indicates a
-block-device along with the starting sector and size of the region. The source
-of the copy is given as one io_region structure, and the destinations of the
-copy are given as an array of io_region structures.
- struct io_region {
- struct block_device *bdev;
- sector_t sector;
- sector_t count;
- };
-To start the copy, the user calls kcopyd_copy(), passing in the client
-pointer, pointers to the source and destination io_regions, the name of a
-completion callback routine, and a pointer to some context data for the copy.
- int kcopyd_copy(struct kcopyd_client *kc, struct io_region *from,
- unsigned int num_dests, struct io_region *dests,
- unsigned int flags, kcopyd_notify_fn fn, void *context);
- typedef void (*kcopyd_notify_fn)(int read_err, unsigned int write_err,
- void *context);
-When the copy completes, kcopyd will call the user's completion routine,
-passing back the user's context pointer. It will also indicate if a read or
-write error occurred during the copy.
-When a user is done with all their copy jobs, they should call
-kcopyd_client_destroy() to delete the kcopyd client, which will release the
-associated memory pages.
- void kcopyd_client_destroy(struct kcopyd_client *kc);