Re: Regression! kern/t_pty fails - cannot set pty's queue size

[Paul Goyette <paul%whooppee.com@localhost>]

On Fri, 17 Aug 2012, Paul Goyette wrote:

> Some time between 10:20:07 and 15:50:06 UTC on 2012-08-12, the pty_queue test 
> case for kern/t_pty has been failing.  The error appears to be an EBUSY 
> return from "ioctl(fd, TIOCSQSIZE, &opt)".  This worked correctly in prior 
> test runs, but has been failing consistently since Aug 12.
>
> This would appear to be a result of the following commit:
>
>         Module Name:    src
>         Committed By:   christos
>         Date:           Sun Aug 12 14:45:45 UTC 2012
>
>         Modified Files:
>                 src/sys/kern: tty.c
>
>         Log Message:
>         PR/46780: Dennis Ferguson: Take the easy way out and return EBUSY
>         when changing the queue size if the output queue is not empty.
>         Other solutions seemed too complex/fragile.
>
> Perhaps the "output queue not empty" check isn't working?

The code in question:

        static int
        tty_set_qsize(struct tty *tp, int newsize)
        {
                struct clist rawq, canq, outq;
                struct clist orawq, ocanq, ooutq;

                if (outq.c_cc != 0)
                        return EBUSY;
        ...

It is definitely not obvious to me how outq.c_cc can have any useful 
value at this point - outq has only just been allocated on the stack.



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