Re: Btrfs hangs 3.19-10

[Hugo Mills <hugo@carfax.org.uk>]

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On Sun, Apr 05, 2015 at 03:30:47AM +0000, Russell Coker wrote:
> On Sun, 5 Apr 2015 03:16:21 AM Duncan wrote:
> > Hugo Mills posted on Sat, 04 Apr 2015 13:00:47 +0000 as excerpted:
> > > On Sat, Apr 04, 2015 at 12:55:08PM +0000, Russell Coker wrote:
> > >> As an aside are there options to mkfs.btrfs that would make a
> > >> filesystem mountable by kernel 3.2.65?  If so I'll file a Debian/Jessie
> > >> bug report requesting that a specific mention be added to the man page.
> > > 
> > > Yes, there are. It's probably -O^extref, but if you can show the
> > > dmesg output from the 3.2 kernel on the failed mount (so that it shows
> > > what the actual failure was), we should be able to give you a more
> > > precise answer.
> 
> [698190.987065] Btrfs loaded
> [698190.999992] device fsid 118e2c64-6ce1-4f21-85e2-2d6aea8f0fa5 devid 1 
> transid 426 /dev/sdf1
> [698191.000981] btrfs: disk space caching is enabled
> [698191.000986] BTRFS: couldn't mount because of unsupported optional features 
> (60).

   That's these, I think:

#define BTRFS_FEATURE_INCOMPAT_BIG_METADATA     (1ULL << 5)
#define BTRFS_FEATURE_INCOMPAT_EXTENDED_IREF    (1ULL << 6)

so it's definitely -O^extref. I don't see where big_metadata comes
from, though. That's not a -O option. Try with -O^extref and see where
that gets you. (Also, don't mount the FS on a newer kernel -- it may
be setting big metadata automatically, although it probably shouldn't
do).

   Hugo.

> [698191.018176] btrfs: open_ctree failed
> 
> > So I was thinking about this, and the several other earlier options where
> > support wasn't added until kernel X, and had an idea...
> > 
> > How easy and useful might it be to add to mkfs.btrfs appropriate option-
> > group aliases such that if one knew the oldest kernel one was likely to
> > deal with, all one would need to do for the mkfs would be to set for
> > example, -O3.2, or even simply --3.2 (or maybe even --32), and have
> > mkfs.btrfs automatically set/unset the appropriate options so it would
> > "just work" with that kernel and anything newer?
> 
> That would be really useful.  Also it would be good if the code structure 
> allowed adding extra aliases, so for Debian we could add an option -Owheezy.
> 

-- 
Hugo Mills             | Nostalgia isn't what it used to be.
hugo@... carfax.org.uk |
http://carfax.org.uk/  |
PGP: E2AB1DE4          |

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