Re: [Qemu-devel] [PATCH v5 11/22] block: Allow block devices without files

[Kevin Wolf]

Am 13.12.2013 um 18:10 hat Max Reitz geschrieben:
> blkdebug and blkverify will, in order to retain compatibility, not
> support the field "file" implicitly through bdrv_open(). In order to be
> able to use those drivers without giving a filename anyway, it is
> necessary to be able to have block devices without files implicitly
> opened by bdrv_open(). This is the case, if there was neither a file
> name, a reference to an existing block device to use as a file nor
> options specific to the file.
> 
> Signed-off-by: Max Reitz <address@hidden>
> ---
>  block.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/block.c b/block.c
> index bef4f82..9659eb5 100644
> --- a/block.c
> +++ b/block.c
> @@ -1145,11 +1145,14 @@ int bdrv_open(BlockDriverState *bs, const char 
> *filename, QDict *options,
>      qdict_extract_subqdict(options, &file_options, "file.");
>      file_reference = qdict_get_try_str(options, "file");
>  
> -    ret = bdrv_file_open(&file, filename, file_reference, file_options,
> -                         bdrv_open_flags(bs, flags | BDRV_O_UNMAP), 
> &local_err);
> -    qdict_del(options, "file");
> -    if (ret < 0) {
> -        goto fail;
> +    if (filename || file_reference || qdict_size(file_options)) {
> +        ret = bdrv_file_open(&file, filename, file_reference, file_options,
> +                             bdrv_open_flags(bs, flags | BDRV_O_UNMAP),
> +                             &local_err);
> +        qdict_del(options, "file");
> +        if (ret < 0) {
> +            goto fail;
> +        }
>      }
>  
>      /* Find the right image format driver */
> @@ -1178,7 +1181,7 @@ int bdrv_open(BlockDriverState *bs, const char 
> *filename, QDict *options,

Manually adding more context before the next hunk:

>     if (!drv) {
>         ret = find_image_format(file, filename, &drv, &local_err);
>     }

We can get file == NULL now, which will cause a segfault in
find_image_format. (For a reproducer of the segfault, try
'x86_64-softmmu/qemu-system-x86_64 -drive foo=bar')

Kevin