tree 27f0e53df711b235e1ea8187d57c076a54b5b3cb
parent 0d31c7c200b3dca2aeeaa6f74ff3fd539aad803a
author Denis V. Lunev <den@openvz.org> 1430207218 +0300
committer Stefan Hajnoczi <stefanha@redhat.com> 1432283852 +0100

block/parallels: add prealloc-mode and prealloc-size open paramemets

This is preparational commit for tweaks in Parallels image expansion.
The idea is that enlarge via truncate by one data block is slow. It
would be much better to use fallocate via bdrv_write_zeroes and
expand by some significant amount at once.

Original idea with sequential file writing to the end of the file without
fallocate/truncate would be slower than this approach if the image is
expanded with several operations:
- each image expanding means file metadata update, i.e. filesystem
  journal write. Truncate/write to newly truncated space update file
  metadata twice thus truncate removal helps. With fallocate call
  inside bdrv_write_zeroes file metadata is updated only once and
  this should happen infrequently thus this approach is the best one
  for the image expansion
- tail writes are ordered, i.e. the guest IO queue could not be sent
  immediately to the host introducing additional IO delays

This patch just adds proper parameters into BDRVParallelsState and
performs options parsing in parallels_open.

Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Roman Kagan <rkagan@parallels.com>
Signed-off-by: Roman Kagan <rkagan@parallels.com>
Message-id: 1430207220-24458-26-git-send-email-den@openvz.org
CC: Roman Kagan <rkagan@parallels.com>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>