Re: LVM support

[Tomáš Čech]

On Sun, May 03, 2015 at 09:59:53PM +0200, Ludovic Courtès wrote:
> Sorry for the delay.

Sorry for all the delays :)

> Tomáš Čech <address@hidden> skribis:
>
> > On Tue, Apr 21, 2015 at 05:52:33PM +0200, Ludovic Courtès wrote:
>
> [...]
>
> > > So I would declare
> > >
> > >  (mapped-device
> > >    (source "/dev/sda")
> > >    (target "volume_group_name-logical_volume_name")
> > >    (kind lvm-device-mapping))
> > >
> > > and that would give me
> > > /dev/mapper/volume_group_name-logical_volume_name, right?
> >
> > Volume group can be on multiple block devices. For now I rely on autodetect
> > abilities of LVM.
> >
> > So you would declare:
> >
> > (mapped-device
> >  (source "") ; irrelevant for LVM
> >  (target "volume_group_name")
> >  (type lvm-mapping))
> >
> > and that would give you
> > /dev/mapper/volume_group_name-some_volume
> > /dev/mapper/volume_group_name-other_volume
> > ...
> >
> > and more conveniently
> > /dev/volume_group_name/some_volume
> > /dev/volume_group_name/other_volume
> > ...
>
> OK.  So the ‘source’ is irrelevant because ‘vgscan’ magically creates
> the device nodes for volumes such that users don’t have to know what the
> underlying block devices are, right?

Yes.


> [...]
>
> > > >           (boot-system #:mounts '#$(map file-system->spec file-systems)
> > > >                        #:pre-mount (lambda ()
> > > > -                                    (and address@hidden))
> > > > +                                    (and address@hidden
> > > > +                                         ;; If we activated any volume group, 
> > > > we
> > > > +                                         ;; need to ensure that device nodes 
> > > > are
> > > > +                                         ;; created.  Add code here to call it
> > > > +                                         ;; once for all activations.
> > > > +                                         #$(when (lvm-mapping-used? 
> > > > mapped-devices)
> > > > +                                             #~(zero?
> > > > +                                                (system* (string-append
> > > > +                                                          #$lvm2/static
> > > > +                                                          "/sbin/lvm.static")
> > > > +                                                         "vgscan"
> > > > +                                                         "--mknodes")))))
> > >
> > > So ‘lvm vgchange --activate y’ does not create /dev nodes?
> >
> > Right.
> >
> > > Would it be possible to change the command returned by
> > > ‘logical-volume-group-activate’ to somehow create the nodes?  That would
> > > be ideal.
> >
> > There are two actions needed to be taken:
> > 1] volume group activation
> > 2] creation of nodes
> >
> > This design choice does as many 1] as needed and 2] once in the end.
> >
> > I could do always 1] and 2] for every volume group, but I didn't find it nice,
> > since previous 2] calls are useless only slowing down the process. Do you
> > really think I should change it?
>
> No, you’re right, what you did makes a lot of sense (thanks for bearing
> with me!).

Good.

> Could you send an updated patch?  It sounds like we’re almost there,
> I guess.

Not there yet. Now I need to make some changes with mounting order to help
non-root filesystems on LVM volume.

Right now it seems it tries to:
1] mount all filesystems
2] run udev

But I need to make it:
1] mount /dev
2] run udev service (with the `udevadm settle' in the end)
3] mount the rest of filesystems

It seems that /sys and /proc is mounted already from initrd phase using
mount-essential-file-systems. Is there reason not to put /dev there as well?

I see none so I'll try to add /dev filesystem mounting there (and to
move-essential-file-systems) and remove it from %base-file-systems.

Best regards,

S_W

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