Re: [PATCH v3 11/14] nbd/client: Accept 64-bit block status chunks

[Vladimir Sementsov-Ogievskiy]

On 31.05.23 20:40, Eric Blake wrote:
> On Wed, May 31, 2023 at 08:00:43PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> > On 15.05.23 22:53, Eric Blake wrote:
> > > Because we use NBD_CMD_FLAG_REQ_ONE with NBD_CMD_BLOCK_STATUS, a
> > > client in narrow mode should not be able to provoke a server into
> > > sending a block status result larger than the client's 32-bit request.
> > > But in extended mode, a 64-bit status request must be able to handle a
> > > 64-bit status result, once a future patch enables the client
> > > requesting extended mode.  We can also tolerate a non-compliant server
> > > sending the new chunk even when it should not.
> > >
> > > @@ -672,7 +681,8 @@ static int nbd_parse_blockstatus_payload(BDRVNBDState *s,
> > >         * connection; just ignore trailing extents, and clamp things to
> > >         * the length of our request.
> > >         */
> > > -    if (chunk->length > sizeof(context_id) + sizeof(*extent)) {
> > > +    if (count != wide ||
> >
> > hard to read for me. Could it be simply "count > 1 ||" ?
>
> For existing commands (compact), count is initialized to 0 as it is
> not transferred over the wire.  For extended commands, count is
> transferred over the wire, but we expect it to be 1 (and not 0).
> Comparing count != wide is more precise than checking count > 0 (which
> should never happen for compact, but would be a bug for extended).

The only case you add to the check is when count = 0 for extended. But in this case 
"more than one extent" message is counterintuitive.

> > > +        chunk->length > sizeof(context_id) + wide * sizeof(count) + len) {
> > >            trace_nbd_parse_blockstatus_compliance("more than one extent");
> > >        }
> > >        if (extent->length > orig_length) {
> > > @@ -1117,7 +1127,7 @@ static int coroutine_fn 
> > > nbd_co_receive_cmdread_reply(BDRVNBDState *s, uint64_t h
> > >
> > >    static int coroutine_fn nbd_co_receive_blockstatus_reply(BDRVNBDState *s,
> > >                                                             uint64_t handle, 
> > > uint64_t length,
> > > -                                                         NBDExtent *extent,
> > > +                                                         NBDExtentExt *extent,
> > >                                                             int *request_ret, 
> > > Error **errp)
> > >    {
> > >        NBDReplyChunkIter iter;
> > > @@ -1125,6 +1135,7 @@ static int coroutine_fn 
> > > nbd_co_receive_blockstatus_reply(BDRVNBDState *s,
> > >        void *payload = NULL;
> > >        Error *local_err = NULL;
> > >        bool received = false;
> > > +    bool wide = false;
> > >
> > >        assert(!extent->length);
> > >        NBD_FOREACH_REPLY_CHUNK(s, iter, handle, false, NULL, &reply, &payload) {
> > > @@ -1134,7 +1145,13 @@ static int coroutine_fn 
> > > nbd_co_receive_blockstatus_reply(BDRVNBDState *s,
> > >            assert(nbd_reply_is_structured(&reply));
> > >
> > >            switch (chunk->type) {
> > > +        case NBD_REPLY_TYPE_BLOCK_STATUS_EXT:
> > > +            wide = true;
> > > +            /* fallthrough */
> > >            case NBD_REPLY_TYPE_BLOCK_STATUS:
> > > +            if (s->info.extended_headers != wide) {
> > > +                trace_nbd_extended_headers_compliance("block_status");
> >
> > You set wide to true once, on first "NBD_REPLY_TYPE_BLOCK_STATUS_EXT", and then parse 
> > following "NBD_REPLY_TYPE_BLOCK_STATUS" if the come with wide=true.
> >
> > Should it be:
> >
> > --- a/block/nbd.c
> > +++ b/block/nbd.c
> > @@ -1135,7 +1135,7 @@ static int coroutine_fn 
> > nbd_co_receive_blockstatus_reply(BDRVNBDState *s,
> >       void *payload = NULL;
> >       Error *local_err = NULL;
> >       bool received = false;
> > -    bool wide = false;
> > +    bool wide;
> >       assert(!extent->length);
> >       NBD_FOREACH_REPLY_CHUNK(s, iter, handle, false, NULL, &reply, &payload) {
> > @@ -1146,9 +1146,8 @@ static int coroutine_fn 
> > nbd_co_receive_blockstatus_reply(BDRVNBDState *s,
> >           switch (chunk->type) {
> >           case NBD_REPLY_TYPE_BLOCK_STATUS_EXT:
> > -            wide = true;
> > -            /* fallthrough */
> >           case NBD_REPLY_TYPE_BLOCK_STATUS:
> > +            wide = chunk->type == NBD_REPLY_TYPE_BLOCK_STATUS_EXT;
> >               if (s->info.extended_headers != wide) {
>
> Good observation, since we reach this multiple times in a loop.  I'm
> squashing that in.

--
Best regards,
Vladimir