netbsd-5: panic: ureadc: non-positive resid

[Matthew Mondor <mm_lists%pulsar-zone.net@localhost>]

Under some circumstances, the following panic occurs:
panic: ureadc: non-positive resid

Interestingly, I've been able to reproduce it in the following peculiar
way.

Using a program such as:

#include <sys/types.h>
#include <sys/uio.h>
#include <unistd.h>

int main(void)
{
        struct iovec iov[1];
        char buffer[1024];

        iov[0].iov_base = buffer;
        iov[0].iov_len = 0;

        return preadv(0, iov, 1, 0);
}

which of course, normally fails with EINVAL.  Using readv(2) there also
has the same issue in this particular case.  I paniced this box often
enough for tonight but don't exactly remember if this also happens with
read(2) and length zero.

I can run the above test on the text console alone as much as I want
without issue, yet if I start screen(1) and then run such a command, it
allows to read from stdin and waits there until I press enter, at
which point the panic occurs.

I yet have to build a debug kernel and test this, as well as to run a
RAM check on this system, but wondered if perhaps someone had a clue
about an actual reason this could occur (i.e. a bug in the pty code or
whatever).

Thanks,
-- 
Matt