Re: [REVIEW] User-space support for bad_features2 patch

Eric Sandeen
2008-02-22T17:41:37Z

Barry Naujok wrote:
> The attached patch fixes mkfs.xfs writing the bad features2 in the first
> place (the change to xfs_sb.h does this).
>
> Next xfs_db support printing of this superblock field and xfs_check can
> report the bad_features2 field is set.
>
> xfs_repair can correct the error in the same fashion that David Chinner's
> mount code does it.
>
> This patch applies to the lazy-count xfs_repair conversion code that I
> posted a short time before this patch.
>
> Barry.
>
+ * Check bad_features2, if set and features2 is zero, copy
+ * bad_features2 to features2 and zero bad_features2.
+ */
+ if (sb->sb_bad_features2 != 0) {
+ if (sb->sb_features2 == 0)
+ sb->sb_features2 = sb->sb_bad_features2;
+ sb->sb_bad_features2 = 0;
+ primary_sb_modified = 1;
+ do_warn(_("superblock's features2 field is in the wrong "
+ "location, correcting\n"));
+ }

My only thought here is that if you repair it, then use an older kernel
w/o the fix, suddenly your fs behavior changes, whereas before you often
got lucky, and both userspace & kernelspace swapped the same way, and
you found the bits you were looking for out of luck :) (same goes for
the recent kernel fix too, I guess)

Should we flag the bad_features2 as "already copied to features2" but
otherwise leave it? Hmm I guess that would look like an unsupported
feature flag to old kernels, wouldn't it. Urgh.

-Eric