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).