kcopyd.txt 1.9 KB

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  1. kcopyd
  2. ======
  3. Kcopyd provides the ability to copy a range of sectors from one block-device
  4. to one or more other block-devices, with an asynchronous completion
  5. notification. It is used by dm-snapshot and dm-mirror.
  6. Users of kcopyd must first create a client and indicate how many memory pages
  7. to set aside for their copy jobs. This is done with a call to
  8. kcopyd_client_create().
  9. int kcopyd_client_create(unsigned int num_pages,
  10. struct kcopyd_client **result);
  11. To start a copy job, the user must set up io_region structures to describe
  12. the source and destinations of the copy. Each io_region indicates a
  13. block-device along with the starting sector and size of the region. The source
  14. of the copy is given as one io_region structure, and the destinations of the
  15. copy are given as an array of io_region structures.
  16. struct io_region {
  17. struct block_device *bdev;
  18. sector_t sector;
  19. sector_t count;
  20. };
  21. To start the copy, the user calls kcopyd_copy(), passing in the client
  22. pointer, pointers to the source and destination io_regions, the name of a
  23. completion callback routine, and a pointer to some context data for the copy.
  24. int kcopyd_copy(struct kcopyd_client *kc, struct io_region *from,
  25. unsigned int num_dests, struct io_region *dests,
  26. unsigned int flags, kcopyd_notify_fn fn, void *context);
  27. typedef void (*kcopyd_notify_fn)(int read_err, unsigned int write_err,
  28. void *context);
  29. When the copy completes, kcopyd will call the user's completion routine,
  30. passing back the user's context pointer. It will also indicate if a read or
  31. write error occurred during the copy.
  32. When a user is done with all their copy jobs, they should call
  33. kcopyd_client_destroy() to delete the kcopyd client, which will release the
  34. associated memory pages.
  35. void kcopyd_client_destroy(struct kcopyd_client *kc);