On Tuesday 03 June 2008 17:58, Denys Vlasenko wrote:
> On Tuesday 03 June 2008 16:44, Bernard Blackham wrote:
> > Hi,
> >
> > When I switched from udev+udevd to mdev, booting was much faster and it
> > shaved a decent amount from the total image size. However, I've recently
> > noticed device nodes sometimes disappearing on boot. The specific
> > scenario is:
> >
> > 1. /dev/ttyS1 exists as a device node in the filesystem on boot - prior
> > to the actual device existing, and prior to mdev being called.
> >
> > 2. echo /bin/mdev > /proc/sys/kernel/hotplug
> >
> > 3. a module is loaded that provides ttyS1
> >
> > When this module is loaded, most of the time the existing ttyS1 remains.
> > Sometimes however, it is unlinked from the filesystem and is never seen
> > again (until mdev -s is run, or next boot, maybe).
> >
> > I pointed my hotplug to a script to log what mdev was being called as,
> > and found that when the module is loaded, there is actually a remove
> > event emitted followed by an add event. As there is no locking with
> > mdev, sometimes mdev runs the remove after the add and thus the device
> > node goes missing.
> >
> > udev seems to have gotten around this using a daemon that serialises
> > events based on the sequence number provided by the kernel.
Latest udev I have seems to use netlink.
>From older udev-030:
subsystem = get_subsystem(argv[1]);
if (subsystem == NULL) {
dbg("no subsystem");
goto exit;
}
dbg("subsystem = '%s'", subsystem);
devpath = get_devpath();
if (devpath == NULL) {
dbg("no devpath");
goto exit;
}
dbg("DEVPATH = '%s'", devpath);
action = get_action();
if (action == NULL) {
dbg("no action");
goto exit;
}
dbg("ACTION = '%s'", action);
seqnum = get_seqnum();
if (seqnum == NULL)
seq = -1;
else
seq = atoi(seqnum);
dbg("SEQNUM = '%d'", seq);
You did some debugging and I suspect you can answer this:
is SEQNUM per DEVPATH or is it global? Is there events without SEQNUM at all?
--
vda
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