[Qemu-devel] [PATCH] qcow2: Don't write with BDRV_O_INCOMING

[Qemu-devel] [PATCH] qcow2: Don't write with BDRV_O_INCOMING

[Kevin Wolf]

qcow2_open() causes writes when repairing an image with the dirty flag
set and when clearing autoclear flags. It shouldn't do this when another
qemu instance is still actively working on this image file.

One effect of the bug is that images may have a cleared dirty flag while
the migration source host still has it in use with lazy refcounts
enabled, so refcounts are not accurate and the dirty flag must remain
set.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/qcow2.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index b5b1e8c..da82646 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -644,7 +644,7 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
     }
 
     /* Clear unknown autoclear feature bits */
-    if (!bs->read_only && s->autoclear_features != 0) {
+    if (!bs->read_only && !(flags & BDRV_O_INCOMING) && s->autoclear_features) {
         s->autoclear_features = 0;
         ret = qcow2_update_header(bs);
         if (ret < 0) {
@@ -657,7 +657,7 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
     qemu_co_mutex_init(&s->lock);
 
     /* Repair image if dirty */
-    if (!(flags & BDRV_O_CHECK) && !bs->read_only &&
+    if (!(flags & (BDRV_O_CHECK | BDRV_O_INCOMING)) && !bs->read_only &&
         (s->incompatible_features & QCOW2_INCOMPAT_DIRTY)) {
         BdrvCheckResult result = {0};
 
@@ -1137,10 +1137,12 @@ static void qcow2_close(BlockDriverState *bs)
     /* else pre-write overlap checks in cache_destroy may crash */
     s->l1_table = NULL;
 
-    qcow2_cache_flush(bs, s->l2_table_cache);
-    qcow2_cache_flush(bs, s->refcount_block_cache);
+    if (!(bs->open_flags & BDRV_O_INCOMING)) {
+        qcow2_cache_flush(bs, s->l2_table_cache);
+        qcow2_cache_flush(bs, s->refcount_block_cache);
 
-    qcow2_mark_clean(bs);
+        qcow2_mark_clean(bs);
+    }
 
     qcow2_cache_destroy(bs, s->l2_table_cache);
     qcow2_cache_destroy(bs, s->refcount_block_cache);
-- 
1.8.1.4

Re: [Qemu-devel] [PATCH] qcow2: Don't write with BDRV_O_INCOMING

[Eric Blake]

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On 03/11/2014 08:15 AM, Kevin Wolf wrote:
> qcow2_open() causes writes when repairing an image with the dirty flag
> set and when clearing autoclear flags. It shouldn't do this when another
> qemu instance is still actively working on this image file.
> 
> One effect of the bug is that images may have a cleared dirty flag while
> the migration source host still has it in use with lazy refcounts
> enabled, so refcounts are not accurate and the dirty flag must remain
> set.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/qcow2.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: [Qemu-devel] [PATCH] qcow2: Don't write with BDRV_O_INCOMING

[Stefan Hajnoczi]

On Tue, Mar 11, 2014 at 03:15:03PM +0100, Kevin Wolf wrote:
> qcow2_open() causes writes when repairing an image with the dirty flag
> set and when clearing autoclear flags. It shouldn't do this when another
> qemu instance is still actively working on this image file.
> 
> One effect of the bug is that images may have a cleared dirty flag while
> the migration source host still has it in use with lazy refcounts
> enabled, so refcounts are not accurate and the dirty flag must remain
> set.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/qcow2.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)

Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan