On Wed, Sep 21, 2016 at 04:50:12PM +0200, David Sterba wrote: > On Thu, Aug 18, 2016 at 01:33:27PM -0700, Omar Sandoval wrote: > > > Omar, looks like we need to make the patched kernel refuse to mount free > > > space trees without a new incompat bit set. That way there won't be any > > > surprises for the people that have managed to get a free space tree saved. > > > Can it please printk a message about clearing the tree and mounting again? > > > > > > -chris > > > > Sorry it took me a month to get around to this, I tried to implement > > this a couple of ways but I really don't like it. Basically, when we see > > that we're missing the compat bit, we have to assume that the free space > > tree was created with the same endianness that we're running on now. > > That could lead to a false positive if, say, we created the filesystem > > on a little-endian machine with an old kernel but are using it on a > > big-endian system, or a false negative if it was created on a big-endian > > machine with an old kernel but we're using it on a little-endian > > machine. > > > > There's also the question of making it a compat bit vs an incompat bit. > > An incompat bit makes sure that we don't break the filesystem by > > mounting it on an old big-endian kernel, but needlessly breaks > > backwards-compatibility for little-endian. > > > > I'd be much happier if we could just pretend this never happened. Here's > > the patch, anyways, for the sake of completeness. Chris, what do you > > think? > > Here's my proposal how to resolve this: > > * we have reports from people using intel hw that FST works fine for > them, so here I don't see any need to introduce incompat bits > > * there are few users on bigendian machines, they need to update kernel > to store the correct layout of FST bitmap > > * as majority of user will never hit the BE/LE problem, I'd focus on > advising how to reset the free space tree and let anybody update (ie. > pretend this hasn't happened) > > I don't think we absolutelly must introduce the incompat bit and prevent > a disaster, because there are very few users affected.
Thanks, Dave, that's what I was thinking, too. I'll rebase this series and send it out as is. Hopefully we can get it in for 4.9, or 4.10 at the latest. -- Omar -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
