initrd.scripts: mount_devfs: check whether devtmpfs is mounted on /dev

[Karlson2k]

If tmpfs is used for /dev, it is not enough to check whether tmpfs is mounted somewhere as it could be used for other reasons.
Also ensure that devtmpfs is mounted at the right mountpoint (/dev) and not somewhere else.

[Whissi]

mount_devfs() is only called once, early in linuxrc. Please explain how this should become a problem.

[Karlson2k]

Hi @Whissi.
Two points.

1. It could be nested initramfs.
2. Even with single initramfs my check is faster and guarantee that any accidental future changes will not break the things.

[robbat2]

what you've proposed isn't quite the same.

• if /foobar was mounted with devtmpfs; then this block also wrongly did not fire, which is the bug you're trying to fix.
• previously, if devtmpfs was present, but /dev was mounted with regular tmpfs, this if block did NOT fire.

I think your grep test is expressed more clearly with:
awk -v devfs=$devfs 'BEGIN{rc=1}($2=="/dev" && $3==devfs){rc=0}END{exit rc}' /proc/mounts

If you agree and can rebase with that fix, i'll be happy to merge it, but I agree it shouldn't matter in normal boot cases.