On 02.05.2016 17:35, Kevin Wolf wrote: > Am 26.04.2016 um 23:32 hat Max Reitz geschrieben: >> If the backing file is overridden, this most probably does change the >> guest-visible data of a BDS. Therefore, we will need to consider this in >> bdrv_refresh_filename(). >> >> Adding a new field to the BDS is not nice, but it is very simple and >> exactly keeps track of whether the backing file has been overridden. >> >> Signed-off-by: Max Reitz <mre...@redhat.com> > > What about live snapshots or block jobs that manipulate bs->backing? > They don't use bdrv_open_backing_file(), but bdrv_append() or > bdrv_replace_in_backing_chain() in order to assign a backing file, which > may or may not be the same as in the image header.
I'll take a look into each case, thanks.
> Also, do we want to consider a backing file overridden when the user
> specified it explicitly, but it matches the image header?
For simplicity's sake, I would. I think we've realized before that
trying to identify whether to file names point to the same image is
rather difficult.
Max
>
> Kevin
>
>> block.c | 2 ++
>> include/block/block_int.h | 1 +
>> 2 files changed, 3 insertions(+)
>>
>> diff --git a/block.c b/block.c
>> index e349e83..e178488 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -1299,6 +1299,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict
>> *parent_options,
>>
>> reference = qdict_get_try_str(parent_options, bdref_key);
>> if (reference || qdict_haskey(options, "file.filename")) {
>> + bs->backing_overridden = true;
>> backing_filename[0] = '\0';
>> } else if (bs->backing_file[0] == '\0' && qdict_size(options) == 0) {
>> QDECREF(options);
>> @@ -1589,6 +1590,7 @@ static int bdrv_open_inherit(BlockDriverState **pbs,
>> const char *filename,
>> backing = qdict_get_try_str(options, "backing");
>> if (backing && *backing == '\0') {
>> flags |= BDRV_O_NO_BACKING;
>> + bs->backing_overridden = true;
>> qdict_del(options, "backing");
>> }
>>
>> diff --git a/include/block/block_int.h b/include/block/block_int.h
>> index 10d8759..d73e9ce 100644
>> --- a/include/block/block_int.h
>> +++ b/include/block/block_int.h
>> @@ -409,6 +409,7 @@ struct BlockDriverState {
>> char backing_file[PATH_MAX]; /* if non zero, the image is a diff of
>> this file image */
>> char backing_format[16]; /* if non-zero and backing_file exists */
>> + bool backing_overridden; /* backing file has been specified by the user
>> */
>>
>> QDict *full_open_options;
>> char exact_filename[PATH_MAX];
>> --
>> 2.8.0
>>
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