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

[Eric Blake]

On 2/11/20 7:24 PM, 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

I need to quit pushing things before letting 'make check' finish; this 
change now makes test-reopen-retry-fail.sh hang with a different assertion:

> 
>   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);

this code is not always true.  I'm pushing the fixup as well.

> +  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);
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org