On Thu, May 05, 2016 at 11:39:34AM +0200, Clemens Ladisch wrote: > 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.) Thanks for the explaination guys. I definitely agree that all the return values should be consistent. I am happy to change the values if people prefer but I guess the decision really rests with Takashi and if he is happy to change the returns to POLLERR | POLLHUP, as I guess there is the potential for some user-space fall out. Perhaps I should do this as a seperate patch on top of this chain, so we can review explicitly. I have had a look and both tinyalsa and alsalib look like they would handle the change correctly. Thanks, Charles _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
