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

[Garmine 42]

I would like to avoid modifying rootflags inside grub config so if I
change anything in fstab I don't have to change that in other places
as well. Unless grub-mkconfig can somehow be taught to parse fstab and
set the rootflags according to it.

On 20 January 2016 at 21:43, Devon Smith <devo8604 at gmail.com> wrote:
> Garmine,
>     If you are using grub2 you should be able to add that option in
> your grub config, then regenerate it, that will make that option
> permanent and you wont have to add it every time at boot. Also, if
> 'ro' is in your kernel params at boot, then im pretty sure masking the
> remount service will ensure that your root remains mounted ro...
>
> Devon
>
> On Wed, Jan 20, 2016 at 1:34 PM, Garmine 42 <mikro001 at gmail.com> wrote:
>> 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
>>> GPG fingerprints: DA92 034D B4A8 EC51 7EA6  20DF 9291 EE8A 043C B8C4
>>>                   C0DF 20D0 C075 C3F1 E1BE  775A A7AE F6CB 164B 5A6D