Bug#769702: lvm2: Initscripts cause non bootable system with btrfs root spanned onto lvm

[Roger Gammans]

On Sat, 2014-11-15 at 19:13 +0100, Bastian Blank wrote:
> Control: severity -1 important
> Control: tags -1 moreinfo
> 
> On Sat, Nov 15, 2014 at 04:37:16PM +0000, Roger Gammans wrote:
> > Justification: breaks the whole system
> 
> No, it breaks only itself.

It renders the root filing system unmountable, admitted given a specific
maybe rare configuration. I'd say that makes that specific system (ie
host/ debian instance) unusable. 

> > When using a btfrs for the root if without the first device being on
> > lvm, but with other devices used in the file system whichi are on lvm
> > then the initscript decicded not to make the vg availble .
> 
> Please describe your setup. 

Everything in one filesystem except /boot.
Root is btrfs.

btrfs fi show is:-
# btrfs fi show
failed to read /dev/sr0
Label: none  uuid: e830647d-84e0-447c-aae7-c63b6b4d1603
        Total devices 2 FS bytes used 132.12GB
        devid    2 size 125.00GB used 98.00GB path /dev/dm-0
        devid    1 size 83.00GB used 69.03GB path /dev/sda1

Btrfs Btrfs v0.19

Boot via grub, kernel cmdline is:- "root=UUID=e830647d-84e0-447c-aae7-c63b6b4d1603 ro quiet "
# pvs
File descriptor 3 (pipe:[10067]) leaked on pvs invocation. Parent PID 3852: -bash
lvd  PV         VG   Fmt  Attr PSize   PFree 
  /dev/sda3  vg01 lvm2 a--  165.89g 40.89g
# lvs
File descriptor 3 (pipe:[10067]) leaked on lvs invocation. Parent PID 3852: -bash
  LV   VG   Attr     LSize   Pool Origin Data%  Move Log Copy%  Convert
  root vg01 -wi-ao-- 125.00g                                         



Is there any other information you need ?

>  Either the device is on lvm or it is not.

That's true for device but not a filesystem. A filesystem can span
multiple devices.

> We don't support setups where multiple different devices for root are
> enabled.

Do you mean a root fs which spans devices, or something else  , and is
"we" debian as a whole, or specifically debian-lvm - I'm not sure what
exactly is not supported , and what user-documentation I would have read
to find out.

I probably won't have used lvm given I had BTRFS, but out of force of
habit  I started by setting up LVM and and got myself mentally tied into
that route. But if this is not supported then something perhaps
btfrs-tools should have emitted a warning, when I tried to add a device
to the root fs.  In hindsight I should have just added sda3 to the root
partition, but it's done now.

I still think the patch (or something similar) I attached creates
minimal problems an solves other issues. Otherwise those of us in this
situation (and similar ) need to manually patch initscripts, which I
would worry about be overwritten by an upgrade . Where as the patch
allows specifying a extra parameter at boot time - to use alternate
behaviour also asked for on other tickets.. This patch just makes thing
less fragile - which is surely a good thing - I can understand you not
wanting to probe for my setup it is an odd one.  But there is a
difference between fully supporting and deliberately making things
difficult.


-- 
Roger Gammans <rgammans at gammascience.co.uk>