Takashi Sakamoto wrote:
On May 4 2016 22:59, Charles Keepax wrote:
if (PCM_RUNTIME_CHECK(substream))
return -ENXIO;
return POLLIN | POLLRDNORM | POLLERR;[...] On the other hand, I think POLLOUT, POLLIN, POLLWRNORM and POLLRDNORM should not be included in the value. PCM_RUNTIME_CHECK() ensures PCM substream or PCM runtime is NULL. This means that subsequent I/O operations are failed, at least for handling PCM frames.
I think it better to return 'POLLERR | POLLHUP'.
To expand on this: POLLIN/POLLOUT imply that it is possible to read/ write data without blocking. Sockets and pipes combine POLLHUP with POLLIN because the read() (or recv()) returns 0 bytes without blocking to indicate the end of the stream.
But in this situation, snd_pcm_read*/write* will always fail, so it is, strictly speaking, indeed not appropriate to set POLLIN/OUT.
On the other hand, PCM devices do include the POLLIN/OUT bits when they are in a wrong state. (This is probably to catch programs that do not check the error bits; with POLLIN/OUT set, these programs will try to read/write, and will then get the error code.)
So for consistency, the bits should be included. (Or the other error case fixed to remove these bits.)
Regards, Clemens