Re: [Qemu-devel] [PATCH v3 22/25] block: Do not copy exact_filename from format file

[Max Reitz]

On 30.11.2016 02:18, Max Reitz wrote:
> If the a format BDS's file BDS is in turn a format BDS, we cannot simply
> use the same filename, because when opening a BDS tree based on a
> filename alone, qemu will create only one format node on top of one
> protocol node (disregarding a potential backing file).
> 
> Signed-off-by: Max Reitz <address@hidden>
> ---
>  block.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/block.c b/block.c
> index ec25cbf..71c14f4 100644
> --- a/block.c
> +++ b/block.c
> @@ -4095,9 +4095,20 @@ void bdrv_refresh_filename(BlockDriverState *bs)
>  
>          bs->exact_filename[0] = '\0';
>  
> -        /* If no specific options have been given for this BDS, the filename 
> of
> -         * the underlying file should suffice for this one as well */
> -        if (bs->file->bs->exact_filename[0] && !generate_json_filename) {
> +        /* We can use the underlying file's filename if:
> +         * - it has a filename,
> +         * - the file is a protocol BDS, and
> +         * - opening that file (as this BDS's format) will automatically 
> create
> +         *   the BDS tree we have right now, that is:
> +         *   - the user did not significantly change this BDS's behavior with
> +         *     some explicit options
> +         *   - no non-file child of this BDS has been overridden by the user
> +         *   Both of these conditions are represented by 
> generate_json_filename.
> +         */
> +        if (bs->file->bs->exact_filename[0] &&
> +            (bs->file->bs->open_flags & BDRV_O_PROTOCOL) &&

This was a nice try, but as it turns out, this flag does not have to
always set for protocol BDSs. A more reliable test is:

!bs->file->bs->file

This test may also be a bit more intuitive: We can copy exact_filename
in one layer from bs->file, but not through two layers.

Max

> +            !generate_json_filename)
> +        {
>              strcpy(bs->exact_filename, bs->file->bs->exact_filename);
>          }
>      }
>

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