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

[lhuang]

On 08/11/2016 12:13 AM, Lennart Poettering wrote:
> 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.

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
>