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contrib: dracut: fix race with root=zfs:dset when necessities required

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This had always worked in my testing, but a user on hardware reported
this to happen 100%, and I reproduced it once with cold VM host caches.

dracut-zfs-generator runs as a systemd generator, i.e. at Some
Relatively Early Time; if root= is a fixed dataset, it tries to
"solve [necessities] statically at generation time".

If by that point zfs-import.target hasn't popped (because the import is
taking a non-negligible amount of time for whatever reason), it'll see
no children for the root datase, and as such generate no mounts.

This has never had any right to work. No-one caught this earlier because
it's just that much more convenient to have root=zfs:AUTO, which orders
itself properly.

To fix this, always run zfs-nonroot-necessities.service;
this additionally simplifies the implementation by:
  * making BOOTFS from zfs-env-bootfs.service be the real, canonical,
    root dataset name, not just "whatever the first bootfs is",
    and only set it if we're ZFS-booting
  * zfs-{rollback,snapshot}-bootfs.service can use this instead of
    re-implementing it
  * having zfs-env-bootfs.service also set BOOTFSFLAGS
  * this means the sysroot.mount drop-in can be fixed text
  * zfs-nonroot-necessities.service can also be constant and always
    enabled, because it's conditioned on BOOTFS being set

There is no longer any code generated at run-time
(the sysroot.mount drop-in is an unavoidable gratuitous cp).

The flow of BOOTFS{,FLAGS} from zfs-env-bootfs.service to sysroot.mount
is not noted explicitly in dracut.zfs(7), because (a) at some point it's
just visual noise and (b) it's already ordered via d-p-m.s from z-i.t.

Backport-of: 3399a30ee0
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
This commit is contained in:
наб
2023-03-28 22:49:50 +02:00
committed by Tony Hutter
parent 33003ecc93
commit 18edf7a3ba
9 changed files with 54 additions and 76 deletions
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man/man7/dracut.zfs.7
+8 -8
View File
@@ -1,6 +1,6 @@
.\" SPDX-License-Identifier: 0BSD
.\"
.Dd April 4, 2022
.Dd March 28, 2023
.Dt DRACUT.ZFS 7
.Os
.
@@ -28,13 +28,13 @@ zfs-import-scan.service \(da \(da | zfs-import-c
zfs-import.target \(-> dracut-pre-mount.service
| \(ua |
| dracut-zfs-generator |
| ____________________/|
| _____________________/|
|/ \(da
| sysroot.mount \(<-\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em dracut-zfs-generator
| | \(da |
| \(da sysroot-{usr,etc,lib,&c.}.mount |
| initrd-root-fs.target \(<-\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em or \(da
| | zfs-nonroot-necessities.service
| sysroot.mount \(<-\(em\(em\(em dracut-zfs-generator
| |
| \(da
| initrd-root-fs.target \(<-\(em zfs-nonroot-necessities.service
| | |
| \(da |
\(da dracut-mount.service |
zfs-snapshot-bootfs.service | |
@@ -42,7 +42,7 @@ zfs-import-scan.service \(da \(da | zfs-import-c
\(da … |
zfs-rollback-bootfs.service | |
| \(da |
| sysroot-usr.mount \(<-\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em/
| /sysroot/{usr,etc,lib,&c.} \(<-\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em\(em/
| |
| \(da
| initrd-fs.target