[Buildroot] [PATCH] package/eudev: tweak initscript
Yann E. MORIN
yann.morin.1998 at free.fr
Mon Oct 20 18:10:45 UTC 2014
Gustavo, All,
On 2014-10-20 14:57 -0300, Gustavo Zacarias spake thusly:
> On 10/20/2014 02:54 PM, Yann E. MORIN wrote:
>
> > Hmmm... This exit won't do much: it exits a sub-shell, so the initscript
> > will still continue...
>
> I've focused on fixing the one problem, i didn't audit the whole script.
Sorry, that was not a critcism of your patch. I just noticed it by
chance...
> >> - udevadm trigger --action=add
> >> - udevadm settle
> >> + udevadm trigger --type=subsystems --action=add
> >> + udevadm trigger --type=devices --action=add
> >> + udevadm settle --timeout=10
> >
> > Why did you add a timeout, and not explain it?
> >
> > Also, are 10 seconds really enough? What happens if a device takes
> > longer than 10s to initialise (and it is needed to boot, like a slow
> > USB mass-storage) ?
>
> It just seems prudent to avoid a stall, but yeah forgot to mention it,
> it's the usual practice in many distros.
Mine has no timeout, but from man udevadm, the default is 120s:
udevadm settle [options]
Watches the udev event queue, and exits if all current events are
handled.
--timeout=seconds
Maximum number of seconds to wait for the event queue to
become empty. The default value is 120 seconds. A value of
0 will check if the queue is empty and always return
immediately.
So, I think 10s are a bit too short, but can not really suggest a better
default. Maybe we could just keep the default timeout, even though it is
a bit long?
Whether we wait 10 or 120 seconds, if something's stuck, there's not
much we can do about it. My distro, however, does this:
# wait for the udevd childs to finish
log_action_begin_msg "Waiting for /dev to be fully populated"
if udevadm settle; then
log_action_end_msg 0
else
log_action_end_msg 0 'timeout'
fi
Which we could actually do (except in a simpler way, like log the
issue).
> You've got rootwait & friends for that, remember this is post mount-root
> so it doesn't matter there.
Not only USB mass-storage for root, but eth over USB, too. I've seen a
USB bus take about 8s to properly initialise and enumerate all the
devices, and a few seconds more for the USB-eth device to show up, and
there was an NFS resource to be mounted from /etc/fstab.
Anyway, this is a corner case.
Reviewed-by: "Yann E. MORIN" <yann.morin.1998 at free.fr>
Regards,
Yann E. MORIN.
> And if you're doing initramfs then
> switching/pivoting to some other root, well, you're scripting it, you
> should take care of it there since you're doing the mount.
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