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UDev follows the kernel given name, and re-uses the kernel created
device node. If the kernel and spcecified udev rules disagree, the
udev specified node node is created and the kernel-created on is
deleted.
On Thu, Apr 23, 2009 at 11:39, Alan Jenkins <alan-jenkins@tuffmail.co.uk> wrote:
> I'm puzzled by this function:
>
> /* if we have not seen this seqnum, check if it is/was already queued */
> if (seqnum < udev_queue->last_seen_udev_seqnum) {
> udev_queue_get_udev_seqnum(udev_queue);
> if (seqnum < udev_queue->last_seen_udev_seqnum)
>
> Shouldn't the test be (seqnum > udev_queue->last_seen_udev_seqnum) ?
Messages send back by the udev daemon to the netlink socket are
multiplexed by the kernel and delivered to multiple clients. The
clients can upload a socket filter to let the kernel drop messages
not belonging to a certain subsystem. This prevent needless wakeups
and message processing for users who are only interested in a
subset of available events.
Recent kernels allow untrusted users to listen to the netlink
messages.
The messages send by the udev daemon are versioned, to prevent any
custom software reading them without libudev. The message wire format
may change with any udev version update.
For added protection, ignore any unicast message received on the
netlink socket or any multicast message on the kernel group not
received from the kernel.
Signed-off-by: Scott James Remnant <scott@ubuntu.com>
The netlink socket is now used by udev event processes. We should take
care not to pass it to the programs they execute. This is the same way
the inotify fd was handled.
Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
Instead of of our own private monitor socket, we send the
processed event back to our netlink socket, to the multicast
group 2 -- so any number of users can listen to udev events,
just like they can listen to kernel emitted events on group 1.
On Wed, Mar 18, 2009 at 16:00, Matthias Schwarzott <zzam@gentoo.org> wrote:
found out how the error occurs:
It is a difference between
A. udevadm test /sys/class/mem/null/
and
B. udevadm test /sys/class/mem/null
Case A was the case that showed the error behaviour. It seems udevadm is
confused by the trailing slash. This behaviour seems to be there since ages.
There's still a slight race condition when using udevadm settle, if the
udev daemon has a pending inotify event but hasn't yet generated the
"change" uevent for it, the kernel and udev sequence numbers will match
and settle will exit.
Now udevadm settle will send a control message to udevd, which will
respond by sending SIGUSR1 back to the waiting udevadm settle once it
has completed the main loop iteration in which it received the control
message.
If there were no pending inotify events, this will simply wake up the
udev daemon and allow settle to continue. If there are pending inotify
events, they are handled first in the main loop so when settle is
continued they will have been turned into uevents and the kernel
sequence number will have been incremented.
Since the inotify event is pending for udevd when the close() system
call returns (it's queued as part of the kernel handling for that system
call), and since the kernel sequence number is incremented by writing to
the uevent file (as udevd does), this solves the race.
When the settle continues, if there were pending inotify events that
udevd had not read, they are now pending uevents which settle can wait
for.
Signed-off-by: Scott James Remnant <scott@ubuntu.com>
