Re: [Qemu-devel] [PATCH v4] snapshot: fixed bdrv_get_full_backing_filename can not get correct full_backing_filename

[Jun Li <junmuzi@gmail.com>]

please ignore this one.

On 05/18/2014 05:01 PM, Jun Li wrote:
> This patch fixed bdrv_get_full_backing_filename can not calculate the correct full path name for backing_file via path_combine.
>
> Such as:
> create a snapshot chain:
> $BASE_IMG<-sn1<-sn2
> backing file is : /home/wookpecker/img.qcow2
> sn1 : /home/woodpecker/tmp/sn1
> sn2 : /home/woodpecker/tmp/sn2
> when create sn2, path_combine can not got a correct path for $BASE_IMG.
>
> In this patch, will check the backing_filename is a symlink or not firstly,
> then return the full(absolute) path via realpath.
>
> Signed-off-by: Jun Li <junmuzi@gmail.com>
> ---
> This is v4 of the patch. This version is the same with v3. Only difference is the commit description.
> What does this patch has fixed, please ref following bug(it gives the detailed description):
> https://bugzilla.redhat.com/show_bug.cgi?id=1084302
> ---
>   block.c | 18 +++++++++++++++++-
>   1 file changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/block.c b/block.c
> index c90c71a..d163a8c 100644
> --- a/block.c
> +++ b/block.c
> @@ -304,10 +304,26 @@ void path_combine(char *dest, int dest_size,
>   
>   void bdrv_get_full_backing_filename(BlockDriverState *bs, char *dest, size_t sz)
>   {
> +    struct stat sb;
> +    char *linkname;
> +
>       if (bs->backing_file[0] == '\0' || path_has_protocol(bs->backing_file)) {
>           pstrcpy(dest, sz, bs->backing_file);
>       } else {
> -        path_combine(dest, sz, bs->filename, bs->backing_file);
> +        if (lstat(bs->backing_file, &sb) == -1) {
> +            perror("lstat");
> +            exit(EXIT_FAILURE);
> +        }
> +
> +        /* Check linkname is a link or not */
> +        if (S_ISLNK(sb.st_mode)) {
> +            linkname = malloc(sb.st_size + 1);
> +            readlink(bs->backing_file, linkname, sb.st_size + 1);
> +            linkname[sb.st_size] = '\0';
> +            realpath(linkname, dest);
> +        } else {
> +            realpath(bs->backing_file, dest);
> +        }
>       }
>   }
>