[alsa-devel] Miscellaneous ioplug questions

[Rob Duncan]

Hi Takashi,

>> - Should the poll FD be made writeable as soon as data is available, or
>>   only when at least avail_min is available?
>
> The latter.  Again, ioplug emulates the hardware driver, so the poll
> should behave same as the hardware driver does.
> (Though, admittedly, not all plugin implementations follow this
> strictly....)

So, the poll FD must be readable while there is at least avail_min in
the buffer, and must NOT be readable if there is less than avail_min.
Is that right?

To labor the point a bit, if exactly avail_min becomes available the
poll FD must be made readable.  If a single frame is now transferred, so
the buffer has (avail_min - 1) available, what must the state of the
poll FD be?

A couple more questions:

If we are configured to do blocking operations must the read and write
callbacks always transfer the full requested size, or can they do
partial transfers?

On the other hand, what if we are configured to do non-blocking
operations?

Or does the caller guarantee not to request a transfer larger than what
the ioplugin reports as available?

Thanks,

Rob.