On 08/11/2016 12:13 AM, Lennart Poettering wrote:
On Wed, 10.08.16 05:44, Luyao Huang (lhu...@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.

Hi Lennart,

Thanks for your quick reply and your reply is really helpful. I will have a try to debug kernel and see what kernel does for a new scsi disk partition.

Have a nice day !

BR,
Luyao
Lennart


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