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[Qemu-block] [PATCH v8 09/10] qcow2: Point to amend function in check

From: Max Reitz
Subject: [Qemu-block] [PATCH v8 09/10] qcow2: Point to amend function in check
Date: Wed, 18 Mar 2015 16:56:27 -0400

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

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 <address@hidden>
Reviewed-by: Eric Blake <address@hidden>
Reviewed-by: Stefan Hajnoczi <address@hidden>
 block/qcow2-refcount.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index f7e5b5e..46f999c 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -1340,6 +1340,9 @@ 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");

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