Daniel Smedegaard Buus:
> Sorry for the slow reply =E2=80=94 I was invaded by a batch of nephews, so =
> had
> to be Merry Uncle for awhile there ;)
Very good. Be a nice uncle.
> First of all, having to go mainline vanilla is not a biggie, I will
> probably have to anyway, as I need to use SCST, and my last attempts
> of building that only worked with mainline kernels.
Then I'd ask you to re-build aufs with CONFIG_AUFS_DEBUG=y and try these
commands.
# mkdir /tmp/a
# mount "loopback ext4 or tmpfs" /tmp/a
# echo 1 > /sys/module/aufs/parameters/debug
# mount -t aufs -o ro,verbose,xino=/tmp/a/xino,
br=/titanic/Downloads/Processed=ro:/titanic/Volumes/XD001=ro
none /Archive
# echo 0 > /sys/module/aufs/parameters/debug
And see the kernel logs.
> Oh, and the ZFS I'm using is the ZFS on Linux one, that is the native
> implementation.
For your information, you may want to read this mail and its thread.
http://www.mail-archive.com/aufs-users%40lists.sourceforge.net/msg04381.html
titled "unable to write via nfs to aufs of zfs branches"
Currently it may not be related to your problem though.
Here are what I am currently guessing.
- Your current (unpatched) aufs doesn't support writable zfs branch, but
supports readonly zfs branch.
- Yet I don't know whether your zfs supports aio_read/write functions or
not.
- I've confirmed that latest aufs supports writable btrfs branch, but
not readonly. It may be the reason why "mount -v -t aufs -o
br:/root/a:/root/b none /root/c" failed.
- Internally aufs uses XINO file (for details, please refer to aufs
manual), and it cannot be put on zfs and btrfs. So you need to add
"xino=path" option. The path should be other than zfs and btrfs.
> First of all, the -o verbose option doesn't seem to make any
> difference =E2=80=94 the logged messages are exactly the same as without.
Hmm... It means I should add more messages in aufs. But this will be
another issue now. Anyway thanx for testing.
> Second of all, I've discovered that all I need to do to mount my
> ZFS-backed AUFS volume is to add ONE source on the EXT4 partition and
> the mount succeeds. (By the way, it seems that I'm not allowed to
> create an AUFS mount with only read-only sources anymore? If I try, I
> always get syslog messages that, "first branch should be rw"?)
Without "-o ro" mount option, at least one writable branch is necessary
for aufs. Otherwise the msg "first branch should be rw" is produced. It
is reasonable, isn't it?
But even if your all branches are specified "=ro" without "-o ro"
option, the mount itself should succeed (as long as the branches are
suppported by aufs). I know you got an error, so we need to investigate
more on that.
----------------------------------------------------------------------
> I also noticed while trying out different sizes of dummy tmpfses to
> find the minimum size needed for aufs to mount successfully, that if
> the tmpfs rw target is too small, say 256k, the mount will fail (with
> the "wrong fs type, ..." message), but the target will be populated
> with ".wh..wh.aufs", ".wh..wh.orph/", and ".wh..wh.plnk/", and any
> attempt at unmounting it will fail with "target is busy", even though
> aufs never mounted...
Aufs should reject being mounted when the writable branch is too small
enough to create these ".wh." entries. The behaviour you saw is OK.
But "target is busy" looks strange. I wonder you might be trying
unmounting the system root? No?
J. R. Okajima
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