Re: make-bcache bug?

Marc MERLIN
2017-05-14T20:19:45Z

On Sun, May 14, 2017 at 10:00:55PM +0200, Kai Krakow wrote:
> Am Sun, 14 May 2017 10:58:40 -0700
> schrieb Marc MERLIN <marc@merlins.org>:
>
> > bcache-tools (1.0.8-2+b1)
> >
> > gargamel:~# make-bcache -C /dev/sde2
> > Already a bcache device on /dev/sde2, overwrite with --wipe-bcache
> > gargamel:~# make-bcache --wipe-bcache -C /dev/sde2
> > Device /dev/sde2 already has a non-bcache superblock, remove it using
> > wipefs and wipefs -a
> >
> > /dev/sde2 is an old bcache I'm reformatting.
> > The first message is correct
> > The 2nd one is not "/dev/sde2 already has a non-bcache superblock"
> >
> > Clearly it can't have a bcache and not a bcache superblock, right?
>
> I don't think that each filesystem puts their superblocks in the same
> position. Plus, there are usually backup superblocks across the area.
>
> So you may well see both warnings and both are correct.
>
> Use wipefs, there seems to be an orphan superblock.

Doesn't wipefs -a clear just 16 bytes or so?
I did it and it fixed my problem, but this block device was a bcache
before, and of course on top of that bcache I then added a filesystem.

Let's test this.
1) I wipefs'ed it
2) I made a new cache device on top
3) I did not put a filesystem or use it, because registration is broken
and still rquires a reboot
bcache: register_cache() error opening sde2: cache_alloc(): -ENOMEM
bcache: register_bcache() error opening /dev/sde2: (null)

4) recreating a new cache on top fo the unused cache, fails again.
Basically the superblock detection is not working right and detects
bcache as a non bcache superblock.

gargamel:/mnt/btrfs_pool2# make-bcache -C /dev/sde2
Already a bcache device on /dev/sde2, overwrite with --wipe-bcache
gargamel:/mnt/btrfs_pool2# make-bcache --wipe-bcache -C /dev/sde2
Device /dev/sde2 already has a non-bcache superblock, remove it using wipefs and wipefs -a

Marc
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