Re: "dynamic" fstab

[Alan Barrett <apb%cequrux.com@localhost>]

On Wed, 13 Mar 2013, iMil wrote:
> For my particular purposes, I hacked /etc/rc.d/fsck_root[1] in 
> order to build a fstab corresponding to the output of `sysctl 
> -n kern.root_device'. It works, but that's ugly. Is there any 
> cleaner way to achieve that trick?

I use "from_mount" in the fs_spec column of /etc/fstab.  This is 
documented in mount(8), but not in fstab(5).  /etc/rc.d/fsck_root 
does not know how to deal with that, but I have an unusual setup 
and use "0" in the fs_passno column to suppress fsck_root.

I'd suggest modifying /etc/rc.d/fsck_root to look for 
fs_spec="from_mount" flag, and use sysctl kern.root_device in that 
case.  It does not have to edit /etc/fstab; it just has to pass 
the correct device name to fsck(8).  We could/should also modify 
fsck(8) to understand fs_spec="from_mount".

--apb (Alan Barrett)