Fix plymouth passphrase prompt with dracut

[paper42]

Motivation and Context

When plymouth is in the initramfs generated by dracut, mounting an encrypted zfs filesystem results in an error

cannot open 'zroot': invalid character ''' in name

This is because plymouth --command is ran which splits the command on spaces which means that zfs-load-key gets the filesystem name enclosed in single quotes (since 13c59bb) and fails.

Similar issue with initramfs: #9193
Similar PR for initramfs where the issue with dracut was also discussed: #9202

Description

This commit fixes it by piping the password directly to the command similar to how it's done in other scripts (initramfs, dracut without plymouth).

How Has This Been Tested?

I tested this on my laptop both with plymouth in the initramfs and without.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[behlendorf]

@belperite @ghfields I was hoping since you tackled a similar issue in #9202 I could convince you to review this related fix.

[ahesford]

Ping; I'm wondering if we should pull this patch for void-linux/void-packages#31644

[behlendorf]

If you can verify this does resolve the issue it should be safe to pull. If you are able to test it locally please let us know and we can pull it in as well, it's just been blocked on review/testing.

[ahesford]

Unfortunately, I don't use plymouth, but the change looks to work as intended. I'll let the Void PR gel for a few days in case those you tagged have a chance to review here, but I'm inclined to accept it unless you all discover something unexpected.

[bghira]

i have strong doubts that this will work, as i've worked on this before for other projects, plymouth is particular about how this is done.

[ericonr]

This is known to work; as explained in the PR description, @paper42 has tested it on a physical device.

[behlendorf]

Alright, we'll go ahead and move forward with this change. As mentioned in the PR description we've already made a very similar initramfs change for exactly this reason and it's been tested by the author.