This patch introduces dm_kcopyd_zero() to make it easy to use
kcopyd to write zeros into the requested areas instead
instead of copying.  It is implemented by passing a NULL
copying source to dm_kcopyd_copy().

The forthcoming thin provisioning target uses this.
Signed-off-by: NMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>

If we write a full chunk in the snapshot, skip reading the origin device
because the whole chunk will be overwritten anyway.

This patch changes the snapshot write logic when a full chunk is written.
In this case:
  1. allocate the exception
  2. dispatch the bio (but don't report the bio completion to device mapper)
  3. write the exception record
  4. report bio completed

Callbacks must be done through the kcopyd thread, because callbacks must not
race with each other.  So we create two new functions:

  dm_kcopyd_prepare_callback: allocate a job structure and prepare the callback.
  (This function must not be called from interrupt context.)

  dm_kcopyd_do_callback: submit callback.
  (This function may be called from interrupt context.)

Performance test (on snapshots with 4k chunk size):
  without the patch:
    non-direct-io sequential write (dd):    17.7MB/s
    direct-io sequential write (dd):        20.9MB/s
    non-direct-io random write (mkfs.ext2): 0.44s

  with the patch:
    non-direct-io sequential write (dd):    26.5MB/s
    direct-io sequential write (dd):        33.2MB/s
    non-direct-io random write (mkfs.ext2): 0.27s
Signed-off-by: NMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>

Return client directly from dm_kcopyd_client_create, not through a
parameter, making it consistent with dm_io_client_create.
Signed-off-by: NMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>

Reserve just the minimum of pages needed to process one job.

Because we allocate pages from page allocator, we don't need to reserve
a large number of pages.  The maximum job size is SUB_JOB_SIZE and we
calculate the number of reserved pages based on this.
Signed-off-by: NMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>

Publish the dm-io, dm-log and dm-kcopyd headers in include/linux.
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>

Rename kcopyd.[ch] to dm-kcopyd.[ch].
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>

Clean up the kcopyd interface to prepare for publishing it in include/linux.
Signed-off-by: NHeinz Mauelshagen <hjm@redhat.com>
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>

Clean up the dm-io interface to prepare for publishing it in include/linux.
Signed-off-by: NHeinz Mauelshagen <hjm@redhat.com>
Signed-off-by: NAlasdair G Kergon <agk@redhat.com>

write_err is an unsigned long used with set_bit() so should not be passed
around as unsigned int.

http://bugzilla.kernel.org/show_bug.cgi?id=10271Signed-off-by: NAlasdair G Kergon <agk@redhat.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!