On 30.07.19 20:53, Eric Blake wrote:
> On 7/30/19 12:25 PM, Max Reitz wrote:
>> Reading the snapshot table can fail. That is a problem when we want to
>> repair the image.
>>
>> Therefore, stop reading the snapshot table in qcow2_do_open() in check
>> mode. Instead, add a new function qcow2_check_read_snapshot_table()
>> that reads the snapshot table at a later point. In the future, we want
>> to handle errors here and fix them.
>>
>> Signed-off-by: Max Reitz <mre...@redhat.com>
>> ---
>> block/qcow2.h | 4 +++
>> block/qcow2-snapshot.c | 58 ++++++++++++++++++++++++++++++++
>> block/qcow2.c | 76 ++++++++++++++++++++++++++++++++----------
>> 3 files changed, 120 insertions(+), 18 deletions(-)
>>
>
>> +++ b/block/qcow2-snapshot.c
>> @@ -321,6 +321,64 @@ fail:
>> return ret;
>> }
>>
>> +int coroutine_fn qcow2_check_read_snapshot_table(BlockDriverState *bs,
>> + BdrvCheckResult *result,
>> + BdrvCheckMode fix)
>> +{
>> + BDRVQcow2State *s = bs->opaque;
>> + Error *local_err = NULL;
>> + int ret;
>> + struct {
>> + uint32_t nb_snapshots;
>> + uint64_t snapshots_offset;
>> + } QEMU_PACKED snapshot_table_pointer;
>> +
>> + /* qcow2_do_open() discards this information in check mode */
>> + ret = bdrv_pread(bs->file, 60, &snapshot_table_pointer,
>> + sizeof(snapshot_table_pointer));
>
> Should that '60' be a named constant or offsetof() expression? (I know,
> you just copied this instance from elsewhere)Well, I copied it from the specification. O:-) You’re completely right. It should be offsetof(QCowHeader, nb_snapshots). (I blame the fact that I had started writing the test by this point, so I was already immersed in so many magic numbers.) > Reviewed-by: Eric Blake <ebl...@redhat.com>
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