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