determining superblock version?

[Emmanuel Florac]

Hi all,

as you know kernel prior to 3.16 won't support properly v5 superblocks.
xfsprogs v 3.2.4 and higher defaults to v5 superblocks. This bit quite
a lot of people a year ago or so, when some distributions shipped 3.2.4
xfsprogs with older kernels.

Anyway, I was surprised to find no easy way to find out the superblock
version of an xfs FS. The best I've come across is

xfs_db /dev/this
sb
p

<snip>
versionnum = 0xb4a5
</snip>

So I suppose that the 5 in the end means that the superblock is v5? Can
anyone confirm please? The man page still pretends that the last number
should be 1 to 4, which is confusing.

Oh by the way I think the trick to create a v4 filesystem with mkfs.xfs
higher than 3.2.4 ( mkfs.xfs -m crc=0,finobt=0 /dev/this ) should be in
the FAQ, with a line like this:

Mounting the filesystem fails, and output from dmesg says "Version 5
superblock detected." What should I do?

v5 superblocks require a kernel v3.16 of higher. If you need your
xfs filesystem to be usable with older kernel, use the following
options to mkfs.xfs :

mkfs.xfs -m crc=0,finobt=0 /dev/this

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