[Libguestfs] [PATCH nbdkit] tls-fallback: Fix filter for new .block_size callback

[Laszlo Ersek]

On 02/16/22 22:41, Richard W.M. Jones wrote:
> This filter doesn't call the next_open function in the non-TLS case,
> and therefore it never opens the plugin.  This leaves the internal
> state of nbdkit a bit strange.  There is no plugin context allocated,
> and the last filter in the chain has a context c_next pointer of NULL.
> 
> This works, provided we intercept every possible callback, check the
> non-TLS case, and prevent it from calling the next function (because
> it would dereference the NULL c_next).
> 
> To avoid a crash in backend_block_size we must therefore provide a
> .block_size callback in this filter.
> ---
>  filters/tls-fallback/tls-fallback.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/filters/tls-fallback/tls-fallback.c b/filters/tls-fallback/tls-fallback.c
> index fab9e58b..b34e0431 100644
> --- a/filters/tls-fallback/tls-fallback.c
> +++ b/filters/tls-fallback/tls-fallback.c
> @@ -138,6 +138,20 @@ tls_fallback_get_size (nbdkit_next *next,
>    return next->get_size (next);
>  }
>  
> +static int
> +tls_fallback_block_size (nbdkit_next *next,
> +                         void *handle,
> +                         uint32_t *minimum,
> +                         uint32_t *preferred,
> +                         uint32_t *maximum)
> +{
> +  if (NOT_TLS) {
> +    *minimum = *preferred = *maximum = 0;
> +    return 0;
> +  }
> +  return next->block_size (next, minimum, preferred, maximum);
> +}
> +
>  static int
>  tls_fallback_can_write (nbdkit_next *next,
>                          void *handle)
> @@ -215,6 +229,7 @@ static struct nbdkit_filter filter = {
>    .open               = tls_fallback_open,
>    .export_description = tls_fallback_export_description,
>    .get_size           = tls_fallback_get_size,
> +  .block_size         = tls_fallback_block_size,
>    .can_write          = tls_fallback_can_write,
>    .can_flush          = tls_fallback_can_flush,
>    .is_rotational      = tls_fallback_is_rotational,
> 

This depends on the series

[Libguestfs] [PATCH nbdkit 0/6] UNFINISHED Advertise block size constraints

right? (I thought I'd skip reviewing that series until the dust settles
on the design, between you and Eric).

Thanks
Laszlo