Re: [PATCH] nbd-client: Support leading / in NBD URI

[Richard W.M. Jones]

On Tue, Feb 11, 2020 at 08:31:01PM -0600, Eric Blake wrote:
> The NBD URI specification [1] states that only one leading slash at
> the beginning of the URI path component is stripped, not all such
> slashes.  This becomes important to a patch I just proposed to nbdkit
> [2], which would allow the exportname to select a file embedded within
> an ext2 image: ext2fs demands an absolute pathname beginning with '/',
> and because qemu was inadvertantly stripping it, my nbdkit patch had
> to work around the behavior.
> 
> [1] https://github.com/NetworkBlockDevice/nbd/blob/master/doc/uri.md
> [2] https://www.redhat.com/archives/libguestfs/2020-February/msg00109.html
> 
> Note that the qemu bug only affects handling of URIs such as
> nbd://host:port//abs/path (where '/abs/path' should be the export
> name); it is still possible to use --image-opts and pass the desired
> export name with a leading slash directly through JSON even without
> this patch.
> 
> Signed-off-by: Eric Blake <address@hidden>
> ---
>  block/nbd.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/block/nbd.c b/block/nbd.c
> index d085554f21ea..82f9b7ef50a5 100644
> --- a/block/nbd.c
> +++ b/block/nbd.c
> @@ -1516,8 +1516,10 @@ static int nbd_parse_uri(const char *filename, QDict 
> *options)
>          goto out;
>      }
> 
> -    p = uri->path ? uri->path : "/";
> -    p += strspn(p, "/");
> +    p = uri->path ? uri->path : "";
> +    if (p[0] == '/') {
> +        p++;
> +    }
>      if (p[0]) {
>          qdict_put_str(options, "export", p);
>      }

Looks reasonable, ACK.

Rich.

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