[Libguestfs] [nbdkit PATCH] server: Correct logic when filter fails .prepare

[Richard W.M. Jones]

On Tue, Feb 11, 2020 at 07:24:43PM -0600, Eric Blake wrote:
> If .prepare fails, we do not want to call .finalize (similar to how if
> .open fails, we do not want to call .close).  However, the logic in
> backend_finalize was checking on the wrong condition ('was the
> connection opened' rather than 'was the connection prepared'), which
> led to an assertion failure.
> 
> Simple reproducer:
> 
> $ nbdkit -U - -f --filter cache --run 'qemu-io -r -c quit $nbd' sh - <<\EOF
> > case $1 in get_size) echo oops >&2; exit 1 ;; *) exit 2 ;; esac
> > EOF
> nbdkit: sh[1]: error: /tmp/nbdkitshYvAQbz/inline-script.sh: oops
> nbdkit: backend.c:206: backend_finalize: Assertion `h->state & HANDLE_CONNECTED' failed.
> qemu-io: can't open device nbd:unix:/tmp/nbdkit60FUTw/socket: Failed to read option reply: Unexpected end-of-file before all bytes were read
> nbdkit: nbdkit command was killed by signal 6
> 
> With this patch, the command now fails gracefully:
> nbdkit: sh[1]: error: /tmp/nbdkitshie18Lp/inline-script.sh: oops
> qemu-io: can't open device nbd:unix:/tmp/nbdkitqvAOlr/socket: Requested export not available
> 
> Fixes: ffa98c8d
> Signed-off-by: Eric Blake <eblake at redhat.com>
> ---
> 
> Pushing this to master and stable-1.16
> 
>  server/backend.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/server/backend.c b/server/backend.c
> index 8bfa8525..753f5cca 100644
> --- a/server/backend.c
> +++ b/server/backend.c
> @@ -221,15 +221,13 @@ backend_finalize (struct backend *b)
>    if (h->state & HANDLE_FAILED)
>      return -1;
> 
> -  if (h->handle) {
> -    assert (h->state & HANDLE_CONNECTED);
> +  assert (h->state & HANDLE_OPEN);
> +  if (h->state & HANDLE_CONNECTED) {
>      if (b->finalize (b, h->handle) == -1) {
>        h->state |= HANDLE_FAILED;
>        return -1;
>      }
>    }
> -  else
> -    assert (! (h->state & HANDLE_CONNECTED));
> 
>    if (b->i)
>      return backend_finalize (b->next);

ACK

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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