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authorDapeng Mi <dapeng1.mi@linux.intel.com>2026-09-17 09:52:33 +0800
committerIngo Molnar <mingo@kernel.org>2026-09-22 11:37:46 +0200
commit0102c8c7fdfc4bd700971daff2b94470f4eafae4 (patch)
tree531306c2299f9a269f0a986e29f17ba972180104 /Documentation/admin-guide/device-mapper/kcopyd.rst
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perf/x86/intel: Rename DMR offcore_rsp attribute to offmodule_rspgrafted
DMR introduces Offmodule Response events in place of the legacy Offcore Response events, but it still exposes the inherited offcore_rsp PMU attribute for programming the corresponding MSR data. Rename the DMR PMU attribute to offmodule_rsp so the sysfs interface matches the underlying event name and avoids user & tooling confusion. Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://patch.msgid.link/20260917015234.981153-12-dapeng1.mi@linux.intel.com
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+======
+kcopyd
+======
+
+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
+kcopyd_client_create()::
+
+ 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);