On Tue, Feb 12, 2013 at 12:06:55PM +0100, Lukas Czerner wrote:
> We should wipe off all the signatures from the device prior the file
> system creation. It is because because some file systems (btrfs) may
> still have their signatures on the device which can be confusing for
> userspace possibly resulting in the unmountable file system.
>
> This patch adds a function which uses libblkid library to wipe all the
> signatures from the device.
>
> If user disables libblkid library or does not have it installed this new
> feature will not be used. This case can be implemented separately.
mkfs.xfs already zeros the first part of the block device regardless
of whether it is using libblkid or not:
....
/* amount (in bytes) we zero at the beginning and end of the device to
* remove traces of other filesystems, raid superblocks, etc.
*/
#define WHACK_SIZE (128 * 1024)
....
/*
* Zero out the beginning of the device, to obliterate any old
* filesystem signatures out there. This should take care of
* swap (somewhere around the page size), jfs (32k),
* ext[2,3] and reiserfs (64k) - and hopefully all else.
*/
mp->m_ddev_targ.dev = xi.ddev;
mp->m_ddev_targ.bt_mount = mp;
buf = libxfs_getbuf(mp->m_ddev_targ, 0, BTOBB(WHACK_SIZE));
memset(XFS_BUF_PTR(buf), 0, WHACK_SIZE);
libxfs_writebuf(buf, LIBXFS_EXIT_ON_FAILURE);
libxfs_purgebuf(buf);
Isn't 128k of zeroing enough to kill existing filesystem signatures?
If not how much is, and why can't we just change WHACK_SIZE to
reflect the size that will kill those signatures that are further
offset into the device?
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
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