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Directory lookups show up in profiling. The queue files are responsible
for a large proportion of file-related system calls in udev coldplug.
Instead of creating a file for each event, append their details to a
log file. The file is periodically rebuilt (garbage-collected) to
prevent it from growing indefinitely.
This single queue file replaces both the queue directory and the
uevent_seqnum file. On desktop systems the file tends not to grow
beyond one page. So it should also save a small amount of memory in
tmpfs.
Tests on a running EeePC indicate average savings of 5% *udevd* cpu time
as measured by oprofile. __link_path_walk is reduced from 1.5% to
1.3%. It is not completely clear where the rest of the gains come from.
In tests running ~400 events, the queue file is rebuilt about 5 times.
Signed-off-by: Alan Jenkins <alan-jenkins@tuffmail.co.uk>
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.
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.
In my scenario, the ntfs prober did *not* detect the presence of a
ntfs filesystem (i.e. vol_id --probe-all returned *only* ext3).
However, if you examine the source of the ntfs prober, it overwrites
the uuid field of the volume_id object long before it actually
decides there's a valid filesystem there - this resulted in vol_id
returning the rather bizarre combination of type=ext3, but a uuid
populated by the ntfs prober.
https://bugs.edge.launchpad.net/ubuntu/+source/udev/+bug/337015
