From 7bae8147abc5661103da3316f09306939ec03708 Mon Sep 17 00:00:00 2001
From: Fam Zheng <famz@redhat.com>
Date: Thu, 5 Sep 2013 08:45:39 +0200
Subject: [PATCH 11/29] vmdk: fix comment for vmdk_co_write_zeroes

RH-Author: Fam Zheng <famz@redhat.com>
Message-id: <1378370739-22259-1-git-send-email-famz@redhat.com>
Patchwork-id: 54100
O-Subject: [RHEL-7 qemu-kvm PATCH] vmdk: fix comment for vmdk_co_write_zeroes
Bugzilla: 995866
RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
RH-Acked-by: Max Reitz <mreitz@redhat.com>

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=995866
Brew:     http://brewweb.devel.redhat.com/brew/taskinfo?taskID=6246791
Upstream: merged

The comment was truncated. Add the missing parts, especially explain why
we need zero_dry_run.

Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(cherry picked from commit 8e50724313895a87057cc243ad805f2eb21feb9f)
Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/vmdk.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 block/vmdk.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/block/vmdk.c b/block/vmdk.c
index a28fb5e..f0c1f93 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -1200,8 +1200,10 @@ static coroutine_fn int vmdk_co_read(BlockDriverState *bs, int64_t sector_num,
 /**
  * vmdk_write:
  * @zeroed:       buf is ignored (data is zero), use zeroed_grain GTE feature
- * if possible, otherwise return -ENOTSUP.
- * @zero_dry_run: used for zeroed == true only, don't update L2 table, just
+ *                if possible, otherwise return -ENOTSUP.
+ * @zero_dry_run: used for zeroed == true only, don't update L2 table, just try
+ *                with each cluster. By dry run we can find if the zero write
+ *                is possible without modifying image data.
  *
  * Returns: error code with 0 for success.
  */
@@ -1328,6 +1330,8 @@ static int coroutine_fn vmdk_co_write_zeroes(BlockDriverState *bs,
     int ret;
     BDRVVmdkState *s = bs->opaque;
     qemu_co_mutex_lock(&s->lock);
+    /* write zeroes could fail if sectors not aligned to cluster, test it with
+     * dry_run == true before really updating image */
     ret = vmdk_write(bs, sector_num, NULL, nb_sectors, true, true);
     if (!ret) {
         ret = vmdk_write(bs, sector_num, NULL, nb_sectors, true, false);
-- 
1.7.1