Re: booting btrfs

[Michael Chang]

On Mon, Dec 30, 2013 at 03:52:36PM +0400, Andrey Borzenkov wrote:
> On Mon, Dec 30, 2013 at 3:28 PM, Vladimir 'φ-coder/phcoder' Serbinenko
> <address@hidden> wrote:
> > On 30.12.2013 11:18, Michael Chang wrote:
> >> On Mon, Dec 23, 2013 at 08:43:34PM -0700, Chris Murphy wrote:
> >>>
> >>> On Dec 23, 2013, at 7:26 PM, Michael Chang <address@hidden> wrote:
> >>>
> >>>> Now I tend to agree that supporting config for snapshot booting
> >>>> shouldn't be upstream's consideration due to it's compliexity and
> >>>> dependency to system, Despite on this, I still like to ask : Did
> >>>> upstream think about any patch trying to provide relative path support
> >>>> for btrfs subvolume name or id's a worthy work or not?
> >>>
> >>> My vague recollection is that it did used to work this way before 2.00, 
> >>> but maybe was unintended?
> >>
> >> It used to follow relative path of set-default volume, but was reverted
> >> to always use absolute path of real root. It's similar to my question
> >> but mine is to have a path intepretation per any subvolume set via
> >> environment variable or so.
> >>
> >> It will work like this way.
> >>
> >> set btrfs_subvol=.snapshot_1
> >> <All path intepretation by the .snapshot_1 subvolume ..>
> >>
> >> set btrfs_subvol=.snapshot_2
> >> <All path intepretation by the .snapshot_2 subvolume ..>
> >>
> >> But this would bring ambiguous path back that I'm not sure a good idea
> >> or not to have such feature.
> >>
> > No. Just add $btrfs_subvol into paths that you want modified.
> 
> I do not think that even this is required. We already have
> ${config_directory} so configuraton simply can be done relative to it.

Thanks for pointing me this. I think we can try to figure out
subvolume dynamically by combining it with ${prefix}. The script would
look like this.

regexp --set=prefix_path "(/.*)" "$prefix"
regexp --set=config_directory_path "(/.*)" "$config_directory"
regexp --set=subvol "(.*)$prefix_path" "$config_directory_path"

if [ -n "$subvol" -a -d "$subvol" ]; then
  rootflags="rootflags=subvol=${subvol}"
else
  rootflags=""
  subvol=""
fi

linux ${subvol}/boot/kernel $rootflags
initrd ${subvol}/boot/initrd

Thanks,
Michael

> 
> >>
> >> Yes. I think this is suggested approch for modifying grub configs.
> >> What bothers me in hooking into grub-mkconfig is it takes time to
> >> finish the "entire" config and will slow down snapshot tools in
> >> creating the snapshot if we hook grub-mkconfig into it's post
> >> processing scripts.
> >>
> >> Does offer an option like `--run-script=90_btrfs_snapshot` to
> >> grub-mkconfig feasible or not? My apologies if this is off topic
> >> here.
> >>
> > Not necessarry.Read my e-mail for explanation on how to do sanely and
> > raise any problems you see with it.
> >
> >
> > _______________________________________________
> > Grub-devel mailing list
> > address@hidden
> > https://lists.gnu.org/mailman/listinfo/grub-devel
> >
> 
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-- 
Michael Chang
Software Engineer
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