Hi,
wipefs is no longer able to show and erase nilfs2 file system
signatures. Bisected this to commit:
5f77ce6 libblkid: (nilfs2) check also backup superblock
Test case on Fedora 21:
# mkfs.nilfs2 /dev/sdb1
# wipefs -V
wipefs from util-linux 2.25.2
# wipefs /dev/sdb1
# wipefs -a /dev/sdb1
Test case on CentOS 7:
# mkfs.nilfs2 /dev/sdb1
# wipefs -V
wipefs from util-linux 2.23.2
# wipefs /dev/sdb1
offset type
-----------------------------------------------------------------
0x406 nilfs2 [filesystem]
UUID: 74b7210c-f568-404f-b302-db0e0339182d
# wipefs -a /dev/sdb1
/dev/sdb1: 2 bytes were erased at offset 0x00000406 (nilfs2): 34 34
So commit 5f77ce6 looks to be about reading either the primary or backup
super block with the highest sequence/checkpoint number. However with a
probe function and no magics wipefs isn't able to detect the file system
or clear the signature bytes.
Re-adding this to libblkid/src/superblocks/nilfs2.c:
.magics = { { .magic="\x34\x34", .len=2, .kboff=1, .sboff=6},
{ NULL }
}
makes wipefs work, but as far as I can tell causes libblkid to use it in
preference to the probefunc so libblkid stops using the backup super
block as a way to identify a nilfs2 file system. Also adding this
doesn't get the signature bytes in the backup super block erased.
Didn't seem to be a way to specify the second magic as being relative to
rounded 4K from the end of the partition.
Hope this analysis is correct. I didn't see a trivial fix so I need to
leave it to the experts.
Thanks,
Mike
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