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[Bug 546860] blkid does not list swap device previously formatted with btrfs
  • From: bugzilla_noreply@xxxxxxxxxx
  • Date: Fri, 5 Feb 2010 01:49:56 +0000
  • Message-id: <20100205014956.A2AC6CC7CD@xxxxxxxxxxxxxxxxxxxxxx>

Dongyang Li <dyli@xxxxxxxxxx> changed:

What |Removed |Added
CC| |dyli@xxxxxxxxxx

--- Comment #2 from Dongyang Li <dyli@xxxxxxxxxx> 2010-02-05 01:49:54 UTC ---
the magic of btrfs sits on the disk with a offset 0x10040(64 * 1024 + 0x40),
while the magic of swap has a offset pagesize() - 10(usually 0xff6).
and mkswap just wipes out the first 1024 bytes of the disk and writes the swap
magic, when blkid checks the disk again, it will see two magics, so that's why
you won't see it with blkid.
blkid and mkswap are both from util-linux-ng, with 2.17, there is a new tool
named wipefs, with which you can see the all magics on the disk, and a simple
wipefs -a /dev/sdXX will simply wipe out all the magics on the disk, then you
can mkswap on it again, and blkid will happily report it as a swap.
the version of util-linux-ng in OpenSUSE 11.2 is 2.16, so you don't have wipefs
right now.

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