diff mbox

[v4,25/26] qcow2: Point to amend function in check

Message ID 1417613866-25890-26-git-send-email-mreitz@redhat.com
State New
Headers show

Commit Message

Max Reitz Dec. 3, 2014, 1:37 p.m. UTC 
If a reference count is not representable with the current refcount
order, the image check should point to qemu-img amend for increasing the
refcount order. However, qemu-img amend needs write access to the image
which cannot be provided if the image is marked corrupt; and the image
check will not mark the image consistent unless everything actually is
consistent.

Therefore, if an image is marked corrupt and the image check encounters
a reference count overflow, it cannot be fixed by using qemu-img amend
to increase the refcount order. Instead, one has to use qemu-img convert
to create a completely new copy of the image in this case.

Alternatively, we may want to give the user a way of manually removing
the corrupt flag, maybe through qemu-img amend, but this is not part of
this patch.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
 block/qcow2-refcount.c | 3 +++
 1 file changed, 3 insertions(+)

Comments

Stefan Hajnoczi Dec. 11, 2014, 2:46 p.m. UTC | #1 
On Wed, Dec 03, 2014 at 02:37:45PM +0100, Max Reitz wrote:
> If a reference count is not representable with the current refcount
> order, the image check should point to qemu-img amend for increasing the
> refcount order. However, qemu-img amend needs write access to the image
> which cannot be provided if the image is marked corrupt; and the image
> check will not mark the image consistent unless everything actually is
> consistent.
> 
> Therefore, if an image is marked corrupt and the image check encounters
> a reference count overflow, it cannot be fixed by using qemu-img amend
> to increase the refcount order. Instead, one has to use qemu-img convert
> to create a completely new copy of the image in this case.
> 
> Alternatively, we may want to give the user a way of manually removing
> the corrupt flag, maybe through qemu-img amend, but this is not part of
> this patch.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> ---
>  block/qcow2-refcount.c | 3 +++
>  1 file changed, 3 insertions(+)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
diff mbox

Patch

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 92f01f3..a656324 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -1370,6 +1370,9 @@  static int inc_refcounts(BlockDriverState *bs,
         if (refcount == s->refcount_max) {
             fprintf(stderr, "ERROR: overflow cluster offset=0x%" PRIx64
                     "\n", cluster_offset);
+            fprintf(stderr, "Use qemu-img amend to increase the refcount entry "
+                    "width or qemu-img convert to create a clean copy if the "
+                    "image cannot be opened for writing\n");
             res->corruptions++;
             continue;
         }