initramfs-zfs should support misc /dev dirs

[Jens Elkner]

Right now 'zfs-initramfs', i.e. /usr/share/initramfs-tools/scripts/zfs does not support any other directory than /dev for "zpool import ...". Therefore even if a pool gets created from a different directory like /dev, say /dev/disk/by-id or /dev/chassis/SYS on next reboot /dev will be used and thus zpool status will show the /dev/sd* etc. on successful import. Beside that now a user does not see the original names used in "zpool create ..." the unstable names like "/dev/sd*" are shown, which is explicitly NOT recommended.

The following patch introduces the "pseudo" kernel param named "zdirs" - a comma separated list of dev dirs to scan on import - which gets used by /usr/share/initramfs-tools/scripts/zfs to honor it.

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "honor misc /dev dirs" seems to be a patch. If it isn't, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are a member of the ~ubuntu-reviewers, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issues please contact him.]

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Richard Laager (rlaager)]

I need to do some testing, but we might want to consider using the cache file. An approach (suggested to my by ryao, I think) was that we first import the root pool read-only, copy the cache file out of it, export the pool, and then import the pool read-write using the cache file.

[Colin Ian King (colin-king)]

@Richard, any followup on that testing?

[Richard Laager (rlaager)]

I haven't had a chance to write and test the zpool.cache copying. I keep meaning to get to it every day, but pushing it back for lack of time.

The zfs-initramfs script in 16.04 (always) and in 18.04 (by default) runs a plain `zpool import`.

ZoL 0.7.5 has a default search order for imports that prefers /dev/disk/by-id:
https://github.com/zfsonlinux/zfs/blob/zfs-0.7.5/lib/libzfs/libzfs_import.c#L1835

That said, so did ZoL on Xenial (0.6.5.6).

On my bionic test VM, non-root pools import using whatever name I created them with. If I use /dev, they import later with /dev. If I use /dev/disk/by-id, they import later with /dev/disk/by-id. This is true immediately, and true across reboots.

Root pools seem to behave the same way. My root pool was created using /dev/disk/by-id per the HOWTO (which I maintain) and is being imported with /dev/disk/by-id. This is with no zpool.cache, either on the live system or in the initramfs (which I unpacked to verify).

In other words, I cannot reproduce this on bionic. I'm pretty confident this is an issue on Xenial, though I haven't re-tested just now to absolutely confirm. But I will say that on my Xenial laptop at the moment, my root pool is imported with a /dev name.

In short, I think this is fixed in Bionic, but I'm not 100% sure which code changed to fix it.