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.
Also, do we want to consider a backing file overridden when the user
specified it explicitly, but it matches the image header?
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
>
