postmarketos-mkinitfs: mount /sysroot/boot from initramfs, not via fstab

Modify postmarketos-mkinitfs and postmarketos-base to mount the boot partition in the initramfs and not in /etc/fstab anymore.

While at it, remove the write_unless_modified logic from postmarketos-base.post-install, because the codepath of not modifying the given file is not useful and even got triggered once although it should not have been (#661 (closed)). The new /etc/fstab modifications are harmless now (and /etc/issue and /etc/motd aren't that important), but it's better to remove the function altogether, before we end up using it for something that is critical in the future.

Find the details in the commit messages.

Documentation

While implementing these fixes, I've updated the boot process and partition layout wiki pages. In particular, they have information about the pmos_boot and pmos_root kernel parameters now, and about the use case of having postmarketOS installed on SD and on eMMC at the same time.

• https://wiki.postmarketos.org/wiki/Boot_process
• https://wiki.postmarketos.org/wiki/Partition_Layout
• https://wiki.postmarketos.org/wiki/Fstab

Test plan

$ pmbootstrap install
(boot up)
$ cat /etc/fstab
$ mount | grep boot  # pay attention to rw/ro

I've verified it myself on qemu-amd64 and pine64-pinephone.

qemu-amd64:~$ cat /etc/fstab 
/dev/cdrom      /media/cdrom    iso9660 noauto,ro 0 0
/dev/usbdisk    /media/usb      vfat    noauto,ro 0 0

# This file is *not* used to mount / or /boot.
# More information: https://postmarketos.org/fstab
qemu-amd64:~$ mount | grep /boot
/dev/vda1 on /boot type ext4 (rw,relatime)

Fixes: #664 (closed), #661 (closed), #258 (closed), #586 (closed)

changed the description

By Oliver Smith on 2020-07-06T23:16:24

added 3 commits

• 08c5759f - main/postmarketos-base: rm write_unless_modified
• abd76c77 - main/postmarketos-mkinitfs: mount /sysroot/boot
• d82bb1d1 - main/postmarketos-base: keep /etc/fstab

Compare with previous version

By Oliver Smith on 2020-07-06T23:18:46

added initramfs type::feature labels

changed the description

By Oliver Smith on 2020-07-07T23:01:07

approved this merge request

By Alexey Min on 2020-07-08T06:52:42

resolved all threads

By Oliver Smith on 2020-07-08T07:58:57

Tested on a5lte and PineTab, both are booting fine..

By Alexey Min on 2020-07-08T10:04:21

approved this merge request

By Bart Ribbers on 2020-07-08T16:02:35

added 14 commits

• d82bb1d1...4cff95a5 - 11 commits from branch master
• 58ae4df2 - main/postmarketos-base: rm write_unless_modified (MR 1398)
• 863ec713 - main/postmarketos-mkinitfs: mount /sysroot/boot (MR 1398)
• 784782f5 - main/postmarketos-base: keep /etc/fstab (MR 1398)

Compare with previous version

By Bart Ribbers on 2020-07-08T16:03:36

enabled an automatic merge when the pipeline for 784782f5 succeeds

By Bart Ribbers on 2020-07-08T16:03:48

merged

By Bart Ribbers on 2020-07-08T16:05:15

Somehow I forgot the cherry pick label.

I've just verified that it works on the v20.05 branch too, with a pinephone and internal eMMC installation.

I'll cherry pick it now.

EDIT: cherry-picked, along with other patches touching postmarketos-base, so we have the same state as in master and patches apply cleanly.

By Oliver Smith on 2020-07-13T22:46:41

added backport-to-v20.05 label

added 1 deleted label and removed type::feature label

mentioned in merge request !1850 (merged)

By Oliver Smith on 2021-01-07T23:37:39