On Friday 06 January 2012 14:52, Natanael Copa wrote:
> Looking a bit at the code, it appears that it never checks for POLLERR
> or POLLHUP and thus enters an endless loop.
>
> Doh... it just hit me.
>
> What happens is, I have an USB keyboard and USB mouse attached to the
> screen. When I power off the screen the keyboard and mouse input
> devices disappear and the file handle in acpid becomes invalid. Since
> nothing checks for POLLERR|POLLHUP it ends up in an endless loop since
> POLLIN was not set.
This is weird, because usually POLLIN would be set too in such a case -
since read() would usually be possible (in a sense that it would not block,
but return EOF or error _immediately_), and therefore poll must indicate that.
Oh well...
> I wonder what the proper way to handle this is. Probably do some
> netlink stuff to detect new devices for acpid?
Another solution is just to restart acpid.
Best to do it automatically from hotplug helper...
> Quick workaround would be to just close fd on POLLHUP or POLLERR:
> diff --git a/util-linux/acpid.c b/util-linux/acpid.c
> index 6e7321b..3d723c0 100644
> --- a/util-linux/acpid.c
> +++ b/util-linux/acpid.c
> @@ -292,6 +292,11 @@ int acpid_main(int argc UNUSED_PARAM, char **argv)
> for (i = 0; i < nfd; i++) {
> const char *event = NULL;
>
> + if (pfd[i].revents & (POLLERR | POLLHUP)) {
> + close(pfd[i].fd);
> + pfd[i].fd = -1;
> + }
> +
I'm a bit surprised this would work: I don't remember any special case
in poll() to ignore fds < 0, so it _might_ start returning POLLNVAL
on this pfd[i] from now on.
Does it work if instead of closing pfd[i].fd, you set pfd[i].events = 0?
A cleaner solution is to shift all pfd[] elements one element down
starting from [i], and do nfd--. Something like this:
if (!(pfd[i].revents & POLLIN)) {
if (pfd[i].revents == 0)
continue; /* this fd has nothing */
/* Likely POLLERR, POLLHUP, POLLNVAL.
* Do not listen on this fd anymore.
*/
close(pfd[i].fd);
nfd--;
for (; i < nfd; i++)
pfd[i].fd = pfd[i + 1].fd;
break; /* do poll() again */
}
With your fix, what happens when you power your screen back on?
I guess the keyboard and mouse ACPI events are no longer detected by acpid,
right?
--
vda
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