On 1/29/13 11:02 AM, Eric Sandeen wrote:
> btrfs sticks superblocks at 64k, 64M, and 256G. If we don't
> overwrite those, libblkid may accidentally identify an ext*
> filesystem with old btrfs superblocks as btrfs, and we'll
> be sad.
>
> libblkid provides a blkid_wipe_fs() functionality to zero
> all existing signatures, but that'd break our handy-dandy
> undo capability, I think. So I'm not sure we have any
> other choice but to do it ourselves.
>
> There is a slight error here in that if the mkfs
> does not span the entire device, we won't overwrite
> signatures past the end of the filesystem, but that case
> should be pretty rare. (The same slight error in logic
> applies to the existing "wipe old MD superblock" path).
Sorry, sent the wrong version, this one does it unconditionally
and doesn't test !noaction. I'll fix that & resend.
Feel free to comment on the general idea, though. :)
-Eric
> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx
> Resolves-RHBZ: 902512
> ---
>
> diff --git a/misc/mke2fs.c b/misc/mke2fs.c
> index bbf477a..e68c705 100644
> --- a/misc/mke2fs.c
> +++ b/misc/mke2fs.c
> @@ -2307,6 +2307,32 @@ static int mke2fs_discard_device(ext2_filsys fs)
> return retval;
> }
>
> +static int mke2fs_wipe_btrfs(ext2_filsys fs)
> +{
> + int blocks; /* nr of blocks to zero */
> + blk64_t start; /* location to zero out */
> + int retval = 0; /* accumulate any failures */
> +
> + blocks = 1;
> + if (fs->blocksize < 4096)
> + blocks = 4096 / fs->blocksize;
> + /*
> + * Wipe out any old btrfs superblocks, at
> + * 64k, 64M, and 256G.
> + */
> + start = 64ULL * 1024 / fs->blocksize;
> + retval += ext2fs_zero_blocks2(fs, start, blocks, NULL, NULL);
> + start = 64ULL * 1024 * 1024 / fs->blocksize;
> + if (start + blocks <= ext2fs_blocks_count(fs->super))
> + retval += ext2fs_zero_blocks2(fs, start, blocks, NULL, NULL);
> + start = 256ULL * 1024 * 1024 * 1024 / fs->blocksize;
> + if (start + blocks <= ext2fs_blocks_count(fs->super))
> + retval += ext2fs_zero_blocks2(fs, start, blocks, NULL, NULL);
> + /* free the static zeroing buffer */
> + ext2fs_zero_blocks2(0, 0, 0, 0, 0);
> + return retval;
> +}
> +
> static void fix_cluster_bg_counts(ext2_filsys fs)
> {
> blk64_t cluster, num_clusters, tot_free;
> @@ -2439,6 +2465,9 @@ int main (int argc, char *argv[])
> itable_zeroed = 1;
> }
> }
> + retval = mke2fs_wipe_btrfs(fs);
> + if (retval)
> + printf(_("Failed to wipe old btrfs super locations\n"));
>
> sprintf(tdb_string, "tdb_data_size=%d", fs->blocksize <= 4096 ?
> 32768 : fs->blocksize * 8);
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
