[arch-projects] [RFC3][PATCH] [mkinitcpio] Cleanly stop udev >= 168 as recommended by upstream.

[Gerardo Exequiel Pozzi]

On 05/02/2011 01:09 PM, Dave Reisner wrote:
> On Mon, May 02, 2011 at 12:28:41PM -0300, Gerardo Exequiel Pozzi wrote:
>> On 05/02/2011 11:23 AM, Thomas Bächler wrote:
>>> Am 02.05.2011 16:00, schrieb Gerardo Exequiel Pozzi:
>>>> N0: device-mapper/LVM udev rules must be parsed for initramfs creation
>>>>      to add OPTIONS+="db_persist"
>>> Patch looks good now.
>> Great!
>>> I am unsure and confused why we would need this db_persist option. In
>>> the past, we killed udev and the db completely and everything worked out
>>> fine. What kind of state would need to be persistent? Is upstream adding
>>> this option?
> We've never killed the DB on leaving early userspace because the DB
> previously lived in /dev/.udev.
Yes, see above.
> We did a mount --move of /dev to
> /new_root/dev and continued on our merry way. Nothing different with the
> DB in /run/udev. We transfer that tmpfs over to the root and everything
> is preserved.
>
Yes.
>> Yes, that is what I not understand, If I am not wrong this was
>> before devtmpfs times.
> Not sure where devtmpfs comes into play. This is all created by udevd in
> userland regardless of the filesystem /dev is mounted on.
>
In old times (about one year ago), "/proc" "/sys" was discarded from 
initramfs [#1]. Also no separate "/dev" exist at initramfs [#2] stage, 
so all "udev DB" was discarded at all.

[#1] 
http://projects.archlinux.org/mkinitcpio.git/commit/init?id=64c0a72e9fc0a83d4313f37e09b2fa5390f2d28d
[#2] 
http://projects.archlinux.org/mkinitcpio.git/commit/init?id=3bb6c683094490e88883b20b5c6cffc17df165e7

>> Maybe this is needed in case if rules on initramfs differs from real
>> root. Dave can you ask to Kay on IRC about this? (I am going to my
>> work now) Thanks.
>>
> Seems to me like lvm2 is just a pain in the ass for udev all around. In
> systemd, it's the only reason that a call to udevadm settle is required
> during late bootup. Everything else can be handled as hotplug events as
> they come up.
>
> Snippets from Kay...
>
> 11:52        kay  » falconindy: only if you use --db-cleanup, and yes lvm
>                      plays dirty tricks with udev and needs the db preserved
> 11:54        kay  » falconindy: they need to catch up with 2011 a bit though
>                      and stop scanning /dev, or have crazy regexes in their
>                      config files
> 11:58        kay  » falconindy: in the past we used to rm -rf /dev/.udev
>                      in the real root
> 11:59 falconindy  » which i assume is a more of a sledgehammer approach
>                      to what the cleanup does
> 12:00        kay  » falconindy: not that different, the db_persist just
>                      adds a sticky bit to the db file
>
> So LVM is just a pain in the butt all around. State can be wiped for all
> other devices and the rebuilt DB in later userspace doesn't contain
> failed/unhandled events from the initramfs.
>
> dave
>
>
Thanks.

-- 
Gerardo Exequiel Pozzi
\cos^2\alpha + \sin^2\alpha = 1