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

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,