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udev rules: Add per-member links in /dev/disk/by-uuid

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The standard udev rules create a `/dev/disk/by-uuid/` link using the
FS's global UUID. This is good. It means the FS UUID can be used to
wait for *any* device that's a member of the FS. But, for a
multi-device file system, users are advised to add the options
`x-systemd.wants=/dev/disk/by-id/xyz` using some ID that's unique to
each specific disk. This way systemd knows to wait for each member. If
any of them times out, the use of `wants` rather than `requires`
allows for a degraded mount to be attempted, if the user has
configured the `degraded` option.

This adds a per-member UUID link in `/dev/disk/by-uuid/` to use for
this purpose.
This commit is contained in:
Will Fancher 2025-10-12 19:22:06 -04:00
parent 38b44ebaf8
commit 5dd424b9f6
1 changed files with 13 additions and 2 deletions
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15
udev/64-bcachefs.rules
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@ -2,7 +2,16 @@
#
# Copyright (C) 2024 Oracle. All rights reserved.
# Author: Darrick J. Wong <djwong@kernel.org>
#
SUBSYSTEM!="block", GOTO="bcachefs_end"
ACTION=="remove", GOTO="bcachefs_end"
ENV{ID_FS_TYPE}!="bcachefs", GOTO="bcachefs_end"
ENV{SYSTEMD_READY}=="0", GOTO="bcachefs_end"
# udev has already assigned a by-uuid link using the FS global
# UUID. We should also have a link for the per-member UUID.
ENV{ID_FS_UUID_SUB_ENC}=="?*", SYMLINK+="disk/by-uuid/$env{ID_FS_UUID_SUB_ENC}"
# Don't let udisks automount bcachefs filesystems without even asking a user.
# This doesn't eliminate filesystems as an attack surface; it only prevents
# evil maid attacks when all sessions are locked.
@ -10,4 +19,6 @@
# According to http://storaged.org/doc/udisks2-api/latest/udisks.8.html,
# supplying UDISKS_AUTO=0 here changes the HintAuto property of the block
# device abstraction to mean "do not automatically start" (e.g. mount).
SUBSYSTEM=="block", ENV{ID_FS_TYPE}=="bcachefs", ENV{UDISKS_AUTO}="0"
ENV{UDISKS_AUTO}="0"
LABEL="bcachefs_end"