On 7/16/26 17:35, Denis V. Lunev wrote:
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> qcow2_do_close() -> qcow2_inactivate() clears the dirty bit with a
> plain write to bs->file, unconditionally. A read-only node can still
> be dirty, inherited from an earlier writable session, and that write
> then hits a missing BLK_PERM_WRITE and asserts in
> bdrv_co_write_req_prepare() (block/io.c) on an entirely ordinary
> close -- closing is expected, the dirty bit on a read-only node
> is not.
>
> Skip the clear for read-only nodes, same as read access already does.
> Any other still-dirty node keeps the unguarded write: it is expected
> to hold write permission, and a missing one there is a bug worth
> seeing.
>
> Signed-off-by: Denis V. Lunev <[email protected]>
> CC: Kevin Wolf <[email protected]>
> CC: Hanna Reitz <[email protected]>
> ---
> block/qcow2.c | 6 +++++-
> tests/qemu-iotests/039 | 11 +++++++++++
> tests/qemu-iotests/039.out | 3 +++
> 3 files changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 2ab6ddd7b0..adb177e6b6 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -2870,7 +2870,11 @@ static int GRAPH_RDLOCK
> qcow2_inactivate(BlockDriverState *bs)
> strerror(-ret));
> }
>
> - if (result == 0) {
> + /*
> + * A read-only node cannot resolve an inherited dirty bit here;
> + * leave it dirty, same as plain read access already does.
> + */
> + if (result == 0 && !bdrv_is_read_only(bs)) {
> qcow2_mark_clean(bs);
> }
>
> diff --git a/tests/qemu-iotests/039 b/tests/qemu-iotests/039
> index e43e7026ce..94a8bfe754 100755
> --- a/tests/qemu-iotests/039
> +++ b/tests/qemu-iotests/039
> @@ -84,6 +84,17 @@ $QEMU_IO -r -c "read -P 0x5a 0 512" "$TEST_IMG" |
> _filter_qemu_io
> # The dirty bit must be set
> _qcow2_dump_header | grep incompatible_features
>
> +echo
> +echo "== Read-only open must not crash on close =="
> +
> +# We must not try to write the QCOW2 header to a read-only image.
> +$QEMU_IMG info --image-opts \
> +
> "driver=$IMGFMT,read-only=on,file.driver=file,file.filename=$TEST_IMG,file.read-only=off"
> \
> + > /dev/null
> +
> +# The dirty bit must still be set: this open never wrote any guest data
> +_qcow2_dump_header | grep incompatible_features
> +
> echo
> echo "== Repairing the image file must succeed =="
>
> diff --git a/tests/qemu-iotests/039.out b/tests/qemu-iotests/039.out
> index 8fdbcc528a..c66361128f 100644
> --- a/tests/qemu-iotests/039.out
> +++ b/tests/qemu-iotests/039.out
> @@ -24,6 +24,9 @@ read 512/512 bytes at offset 0
> 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> incompatible_features [0]
>
> +== Read-only open must not crash on close ==
> +incompatible_features [0]
> +
> == Repairing the image file must succeed ==
> ERROR cluster 5 refcount=0 reference=1
> Rebuilding refcount structure
ping
