Bug 931236

Summary:	sys-apps/systemd systemd-gpt-auto-generator complains of btrfs being backed by /dev/root in the absence of an initramfs
Product:	Gentoo Linux	Reporter:	kfm
Component:	Current packages	Assignee:	Gentoo systemd Team <systemd>
Status:	RESOLVED UPSTREAM
Severity:	normal	CC:	kfm
Priority:	Normal
Version:	unspecified
Hardware:	All
OS:	Linux
See Also:	https://bugs.gentoo.org/show_bug.cgi?id=913413 https://bugs.gentoo.org/show_bug.cgi?id=922809
Whiteboard:
Package list:		Runtime testing required:	---
Bug Depends on:
Bug Blocks:	438380

Description kfm 2024-05-05 08:50:34 UTC

I'm filing this primarily to complement bug 913413. I recently set up two installations that use btrfs, one booting with the "intel-uc.img" initramfs image and the other with no initramfs at all. The latter reported the following:

[    0.854360] BTRFS: device label system devid 1 transid 86094 /dev/root scanned by swapper/0 (1)
[    0.854708] BTRFS info (device sda4): first mount of filesystem 71c15220-db0b-42e6-92eb-7aea008d23eb
[    0.854737] BTRFS info (device sda4): using crc32c (crc32c-intel) checksum algorithm
[    0.854745] BTRFS info (device sda4): using free space tree
[    0.864016] VFS: Mounted root (btrfs filesystem) readonly on device 0:16.
[    0.864054] devtmpfs: mounted

Then, a moment later:

[    1.020388] systemd-gpt-auto-generator[220]: File system behind root file system is reported by btrfs to be backed by pseudo-device /dev/root, which is not a valid userspace accessible device node. Cannot determine correct backing block device.
[    1.022138] (sd-exec-[213]: /usr/lib/systemd/system-generators/systemd-gpt-auto-generator failed with exit status 1.

It proceeds to boot successfully but that's probably because I have a fully populated /etc/fstab; the error message implies that systemd would (at least) not be able to support the Discoverable Partitions Specification under the present circumstances.

Echoing Hadrien's comments in the xfsprogs bug, I don't think that systemd is necessarily in the wrong here. Still, there remains the broader issue of initramfs-less systems being increasingly undermined by the status quo.

Comment 1 Sam James archtester

2024-05-05 08:59:23 UTC

(bug 438380 as a tracker isn't quite a good fit but it's close enough as a way to group related-ish bugs.)

Comment 2 Mike Gilbert gentoo-dev

2024-05-06 17:31:19 UTC

There's nothing for Gentoo to do on this. Please work with the kernel or systemd folks if you want to resolve it.