[systemd-devel] Question about what systemd-udevd will do for a new scsi partition

[Lennart Poettering]

On Wed, 10.08.16 05:44, Luyao Huang (lhuang at redhat.com) wrote:

> Dear list,
> 
> I met a problem that looks like systemd-udevd will make a new scsi disk partition (like /dev/sdb1)
> disappear in a few time. This problem makes libvirt cannot lstat the new scsi disk for a period.
> (you can check this link https://bugzilla.redhat.com/show_bug.cgi?id=1264719).
> And we wrote a script to verify this problem and finally find if we stop systemd-udevd, this will not happen.
> 
> Could you please give me some help and tell me what systemd-udevd does to a new scsi disk partition
> making scsi disk partition disappear in a few time? Thanks in advance for your reply.

udev only propagates kernel events, it does not make up events on its
own. Whenever a new device is reported by the kernel, it will acquire
some additional metadata for it and forward it to clients. Similar,
when a device vanishes it will propagate the event too, with some
additional metadata attached.

Note that udev is also not involved in the creation or removal of
device nodes anymore. it will adjuts access rights and ACLs on
devices, but not create or remove them anymore. That's done by the
kernel directly via devtmpfs.

Long story short: you need to check why the kernel makes the devices
disappear, udev is just the messenger here.

Lennart

-- 
Lennart Poettering, Red Hat