Re: Questionable code in sys/dev/sound/pcm/channel.c

On 26 Jul, Conrad J. Sabatier wrote:
> I'm a little perplexed at the following bit of logic in chn_write()
> (which is where the "interrupt timeout, channel dead" messages are
> being generated).
> 
> Within an else branch within the main while loop, we have:
> 
>             else {
>                 timeout = (hz * sndbuf_getblksz(bs)) /
> (sndbuf_getspd(bs) * sndbuf_getbps(bs));
>                 if (timeout < 1)
>                     timeout = 1;
>                 timeout = 1;
> 
> Why the formulaic calculation of timeout, if it's simply going to be
> unconditionally set to 1 immediately afterwards anyway?  What's going on
> here?

Hmn, looks bogus to me.  I think the intention is to round timeout up to
1 if the result of the formula is zero.  The final assignment statement
looks bogus to me.  Maybe a too short timeout is the source of this
problem.

It looks like this assignment appeared in rev 1.65.

> Also, at the end of the function:
> 
>     if (count <= 0) {
>         c->flags |= CHN_F_DEAD;
>         printf("%s: play interrupt timeout, channel dead\n", c->name);
>     }
> 
>     return ret;
> }
> 
> Could it be that the conditional test is wrong here?  Perhaps
> we should be using (count < 0) instead?
>
> I don't know.  I'm having no small difficulty understanding this code,
> but these two items caught my attention.

I ran into the same problem when I was looking at the code a few days
ago.

BTW, the trace output that was posted showed write() returning 0
immediately before the failure occurred.