Re: [Buildroot] lvm2 seems to require systemd

[Andreas Ziegler <br015@umbiko.net>]

Hi Frank,

On 2024-07-30 09:50, Frank Wunderlich wrote:
> Hi
> 
>> Gesendet: Montag, 22. Juli 2024 um 07:15 Uhr
>> Von: "Andreas Ziegler" <br015@umbiko.net>
>> An: "Frank Wunderlich" <frank-w@public-files.de>
>> Cc: "buildroot" <buildroot@buildroot.org>
>> Betreff: Re: Aw: Re:  Re:  Re: lvm2 seems to require systemd
>> 
>> Hi Frank,
>> 
>> On 2024-07-21 19:37, Frank Wunderlich wrote:
>> > Hi
>> >
>> >> Gesendet: Sonntag, 21. Juli 2024 um 19:58 Uhr
>> >> Von: "Andreas Ziegler" <br015@umbiko.net>
>> >> An: "Frank Wunderlich" <frank-w@public-files.de>
>> >> Cc: "buildroot" <buildroot@buildroot.org>
>> >> Betreff: Re: Aw: Re:  Re: lvm2 seems to require systemd
>> >>
>> >> Hi Frank,
>> >>
>> >> On 2024-07-21 15:50, Frank Wunderlich wrote:
>> >> > Hi Andreas
>> >> >
>> >> > noticed some errors when calling the vgchange command
>> >> >
>> >> > # /usr/sbin/lvm vgchange -aay --autoactivation event vg-nvme
>> >> >   1 logical volume(s) in volume group "vg-nvme" now active
>> >> > [ 8023.796866] udevd[1614]: failed to execute '/usr/sbin/blkid'
>> >> > '/usr/sbin/blkid -o udev -p /dev/dm-0': No such file or directory
>> >> > [ 8023.808977] udevd[1610]: conflicting device node
>> >> > '/dev/mapper/vg--nvme-var' found, link to '/dev/dm-0' will not be
>> >> > created
>> >> > # lvscan
>> >> >   ACTIVE            '/dev/vg-nvme/var' [10.00 GiB] inherit
>> >>
>> >> Your execution of vgchange triggers additional udev messages, that are
>> >> not handled correctly. Try to find out what is missing and add it to
>> >> your image; blkid, for example, is part of package util-linux.
>> >
>> > i have already enabled util_linux
>> > Symbol: BR2_PACKAGE_UTIL_LINUX [=y]
>> > BR2_PACKAGE_HOST_UTIL_LINUX [=y]
>> > BR2_PACKAGE_UTIL_LINUX_LIBBLKID [=y]
>> >
>> > so strange that blkid is not there, but it is in /sbin
>> >
>> > # which blkid
>> > /sbin/blkid
>> >
>> > maybe a symlink needs to be created?
>> >
>> 
>> Sorry, my mistake: blkid is provided by busybox and busybox installs 
>> it
>> in /sbin. Since this is a Buildroot feature (unless you activate
>> BR2_ROOTFS_MERGED_USER), I would modify the udev rule.
>> 
>> >> The double-dash in vg--nvme-var looks strange: is this intentional?
>> >
>> > as you can see above i used only one dash in vg-nvme, not sure why
>> > another one was inserted here
>> >
>> > # pvscan
>> >   PV /dev/nvme0n1p5   VG vg-nvme   lvm2 [<1.79 TiB / <1.78 TiB free]
>> >   Total: 1 [<1.79 TiB] / in use: 1 [<1.79 TiB] / in no VG: 0 [0   ]
>> >
>> >> > but i'm able to mount it
>> >> >
>> >> > # mkdir /mnt/var
>> >> > # mount /dev/mapper/vg--nvme-var /mnt/var/
>> >> > [ 8514.687803] EXT4-fs (dm-0): mounted filesystem
>> >> > be8b31d6-96e2-43a1-8416-a058972118b3 r/w with ordered data mode. Quota
>> >> > mode: disabled.
>> >> > # ls /mnt/var
>> >> > cache       lib         log         lost+found  run         tmp
>> >> > #
>> >> >
>> >> > how can i test the script? currently i'm in the initrd, so changing
>> >> > anything will be lost on reboot, so i want to test the script before
>> >> > putting it into the initrd.
>> >>
>> >> I usually mount the target's file system via ssh://root@hostname in a
>> >> file browser; that allows me to copy to and from the target machine.
>> >> Script and configuration changes are made directly on the target
>> >> system,
>> >> and copied back to the development machine when everything runs
>> >> satisfactorily.
>> >>
>> >> > as far as i see the original call via udev contains some
>> >> > systemd-specific params and environment-vars i do not know currently
>> >>
>> >> They are probably safe to ignore; when in doubt, consult the systemd
>> >> documentation. Evironment variables are extensively used within the
>> >> udev
>> >> context; I doubt that the called lvm2 tool makes use of them.
>> >
>> > they seem to be systemd options which are not stripped by the script
>> > yet which
>> > will result in invalid call (imho only first param is shifted away)
>> >
>> 
>> RUN+="/usr/bin/systemd-run \
>>    --no-block \
>>    --property DefaultDependencies=no \
>>    --unit lvm-activate-$env{LVM_VG_NAME_COMPLETE} \
>>    /usr/sbin/lvm \
>>    vgchange \
>>    -aay \
>>    -autoactivation \
>>    event $env{LVM_VG_NAME_COMPLETE}"
>> 
>> If you put a 'shift 5' at the beginning of the script, it should get 
>> rid
>> of the systemd parameters. Alternatively, you could modify the udev
>> rule.
> 
> I'm not sure how to fix properly....where should i put the script (it 
> is called on bootup and there my changes done on runtime are dropped) 
> and where to call it (imho it should be called by the existing 
> udev-rule, right)?

The script might go into /usr/bin. Put all new or changed files in a 
separate directory, within a layout reflecting that of your root 
filesystem. Configure Buildroot's  BR2_ROOTFS_OVERLAY and these files - 
with their relative directories - will be copied to the root filesystem 
after build and before image creation. For examples, see [1].

> how to fix the blkid properly (maybe add symlink)? but this has to be 
> done in source too or while building.

Leave blkid where it is, modify the udev script and put it in your 
overlay filesystem. As Arnout suggested, reworking all of the udev 
scripts will probably be the easiest approach ...

> sorry for my noob questions, but my buildroot-knowledge is only :)

The Buildroot manual [2] is quite useful. Bootlin has some training 
materials [3] for general use.

Kind regards,
Andreas

> 
> regards Frank
> 

<cut>

[1] https://buildroot.org/downloads/manual/manual.html#customize
[2] https://buildroot.org/docs.html
[3] https://bootlin.com/docs/
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