Re: [Libguestfs] [PATCH nbdkit 3/3] server: filters: Remove struct b_h.

On 2/12/20 7:40 AM, Richard W.M. Jones wrote: >This was previously used as ‘nxdata’ and stored a tuple of ’b->next’ >and the real filter handle. However after recent changes we don't >need it. We can use ‘b->next’ as nxdata, and the handle is passed to >us by the calling functions. > >Inspired by Eric Blakes observations in this email: Blake's >https://www.redhat.com/archives/libguestfs/2020-February/msg00092.html >--- > server/filters.c | 217 ++++++++++++++++------------------------------- > 1 file changed, 73 insertions(+), 144 deletions(-) > >@@ -216,201 +205,181 @@ plugin_magic_config_key (struct backend *b) > static int > next_open (void *nxdata, int readonly) > { >- struct b_h *b_h = nxdata; >+ struct backend *b_next = nxdata; >- return backend_open (b_h->b, readonly); >+ return backend_open (b_next, readonly); > } With this change, 'next_open' and '(int (*)(void *, int))backend_open' now have identical semantics. I'm trying to see if there are further changes we could make that would alleviate the need for function casts. I don't know if it is worth changing nbdkit-filter.h to use 'struct backend *' instead of 'void *' (while leaving struct backend an incomplete type in the public header) - it would be ABI compatible, and although it would require recompilation, we already state that filter recompilation is par for the course (since only plugins promise API compatibility).

But one step at a time; your patch is fine as-is. ACK