[arch-general] Mounting root according to fstab the first time (fstab in initrd)?

[Garmine 42]

On 20 January 2016 at 21:18, Leonid Isaev
<leonid.isaev at jila.colorado.edu> wrote:
> On Wed, Jan 20, 2016 at 09:01:22PM +0100, Garmine 42 wrote:
>> There was a discussion on the linux-btrfs mailing list about this, and
>> for example the btrfs space_cache option can not be changed with a
>> remount - this causes the fstab file's space_cache option to be
>> basically ignored. I want to eliminate this kind of issue on my setup,
>> that's why I need to avoid root being remounted. Instead I want root
>> to be mounted with the options specified in fstab the first (and only)
>> time.
>
> Why is it ignored?
> /dev/sda4 on / type btrfs (ro,nodev,relatime,compress=zlib,ssd,space_cache,autodefrag,subvolid=257,subvol=/_root)
>                                                                ^^^^^^^^^^^

The linux-btrfs discussion suggests that some mount options might be
unchanged after a remount even if it should change based on the fstab.

Although that particular discussion's exact problem was something else
in my opinion, so they might be wrong on that. The fix for that
problem was including the problematic option (space_cache=v2) in the
rootflags parameter. Considering the cmdline size is limited and I
want to avoid modifying that all the time, I want to mount the root
volume with the correct flags in the first place.

> Also, there is fstab in the initramfs:
> $ lsinitcpio /boot/initramfs-linux.img | grep fstab
> etc/fstab

That fstab is an empty file (ran in an uncompreseed initrd):
% wc -c etc/fstab
0 etc/fstab

> Have you tried masking the systemd-remount-fs.service?

First I will try to exclude root= and rootflags= parameters from the
cmdline and include the fstab via mkinitcpio and see if it finds the
root. Do I want to mask remount-fs in this case?

> Cheers,
> --
> Leonid Isaev
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