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From: "Denis V. Lunev" <den@openvz.org>
Date: Tue, 27 Jan 2015 16:51:32 +0300
Message-Id: <1422366699-17473-1-git-send-email-den@openvz.org>
Subject: [Qemu-devel] [PATCH v4 0/7] eliminate data write in
	bdrv_write_zeroes on Linux in raw-posix.c
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Cc: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <famz@redhat.com>, Peter Lieven <pl@kamp.de>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, "Denis V. Lunev" <den@openvz.org>

These patches eliminate data writes completely on Linux if fallocate
FALLOC_FL_ZERO_RANGE or FALLOC_FL_PUNCH_HOLE are  supported on
underlying filesystem.

I have performed several tests with non-aligned fallocate calls and
in all cases (with non-aligned fallocates) Linux performs fine, i.e.
areas are zeroed correctly. Checks were made on
Linux 3.16.0-28-generic #38-Ubuntu SMP

This should seriously increase performance of bdrv_write_zeroes

Changes from v3:
- dropped original patch 1, equivalent stuff was merged already
- reordered patches as suggested by Fam
- fixes spelling errors as suggested by Fam
- fixed not initialized value in handle_aiocb_write_zeroes
- fixed wrong error processing from do_fallocate(FALLOC_FL_ZERO_RANGE)

Changes from v2:
- added Peter Lieven to CC
- added CONFIG_FALLOCATE check to call do_fallocate in patch 7
- dropped patch 1 as NACK-ed
- added processing of very large data areas in bdrv_co_write_zeroes (new
         patch 1)
- set bl.max_write_zeroes to INT_MAX in raw-posix.c for regular files
 (new patch 8)

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
CC: Peter Lieven <pl@kamp.de>
CC: Fam Zheng <famz@redhat.com>