tree 9957b7a2dbdc5047fe1f2be7907f90f5bdb6fbf0
parent 2f012508880f8037590372c24ca6e8b6af8fffb6
author Paul Clements <paul.clements@steeleye.com> 1349396178 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> 1349460324 +0900

nbd: handle discard requests

Add discard support to nbd.  If the nbd-server supports discard, it will
send NBD_FLAG_SEND_TRIM to the client.  The client will then set the flag
in the kernel via NBD_SET_FLAGS, which tells the kernel to enable discards
for the device (QUEUE_FLAG_DISCARD).

If discard support is enabled, then when the nbd client system receives a
discard request, this will be passed along to the nbd-server.  When the
discard request is received by the nbd-server, it will perform:

	fallocate(.. FALLOC_FL_PUNCH_HOLE ..)

To punch a hole in the backend storage, which is no longer needed.

Signed-off-by: Paul Clements <paul.clements@steeleye.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>