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virtual-sink: Fix a crash when moving the sink to a new master right after setup.

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If the virtual sink is moved to a new master right after it has been created,
then the virtual sink input's memblockq can be rewound to a negative read
index. The data written prior to the move starts from index zero, so after the
rewind there's a bit of silence. If the memblockq doesn't have a silence
memchunk set, then pa_memblockq_peek() will return zero in such case, and the
returned memchunk's memblock pointer will be NULL.

That scenario wasn't taken into account in the implementation of
sink_input_pop_cb. Setting a silence memchunk for the memblockq solves this
problem, because pa_memblock_peek() will now return a valid memblock if the
read index happens to point to a hole in the memblockq.

I believe this isn't the best possible solution, though. It doesn't really make
sense to rewind the sink input's memblockq beyond index 0 in the first place,
because now when the stream starts to play to the new master sink, there's some
unnecessary silence before the actual data starts. This is a small problem,
though, and I don't grok the rewinding system well enough to know how to fix
this issue properly.

I went through all files that call pa_memblockq_peek() to see if there are more
similar bugs. play-memblockq.c was the only one that looked to me like it might
be broken in the same way. I didn't try reproducing the bug with
play-memblockq.c, though, so I just added a FIXME comment there.
This commit is contained in:
Tanu Kaskinen 2011-02-24 16:16:43 +02:00 • committed by Colin Guthrie
parent b3644c1bcd
commit 6bd34156b1
3 changed files with 14 additions and 5 deletions
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6
src/pulsecore/play-memblockq.c
View file

@ -135,6 +135,12 @@ static int sink_input_pop_cb(pa_sink_input *i, size_t nbytes, pa_memchunk *chunk
return -1;
}
/* FIXME: u->memblockq doesn't have a silence memchunk set, so
* pa_memblockq_peek() will return 0 without returning any memblock if the
* read index points to a hole. If the memblockq is rewound beyond index 0,
* then there will be a hole. */
pa_assert(chunk->memblock);
chunk->length = PA_MIN(chunk->length, nbytes);
pa_memblockq_drop(u->memblockq, chunk->length);