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

To: Eric Sandeen <sandeen@xxxxxxxxxxx>
Subject: Re: [REVIEW] User-space support for bad_features2 patch
From: Jan Derfinak <ja@xxxxxxxxxxxx>
Date: Mon, 25 Feb 2008 10:55:06 +0100 (CET)
Cc: Barry Naujok <bnaujok@xxxxxxx>, "xfs@xxxxxxxxxxx" <xfs@xxxxxxxxxxx>
In-reply-to: <47C27F63.8070909@sandeen.net>
References: <op.t6w1h5f53jf8g2@pc-bnaujok.melbourne.sgi.com> <47BF0963.6020809@sandeen.net> <op.t611gf1q3jf8g2@pc-bnaujok.melbourne.sgi.com> <47C27F63.8070909@sandeen.net>
Sender: xfs-bounce@xxxxxxxxxxx
On Mon, 25 Feb 2008, Eric Sandeen wrote:

> Barry Naujok wrote:
> > On Sat, 23 Feb 2008 04:41:55 +1100, Eric Sandeen <sandeen@xxxxxxxxxxx>  
> > wrote:
> 
> ...
> 
> >> 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)
> > 
> > I believe the kernel code never tried to access "bad_features2" part
> > of the superblock, it always did the correct thing (correct me if I'm
> > wrong of course :).
> 
> I'm fairly sure that it did; both userspace & kernelspace were doing the
> same thing, and endian-flipping "too much" ... but I'd have to test
> again to be sure.

In my case (x86_64, both kernel and userspace 64-bit), kernel accessed the
right place (features2), but userspace (mkfs.xfs) accessed wrong place
(bad_features2).

After patching mkfs.xfs with your patch, kernel began to use lazy-count
without additional bad_features2 changes.

There seems to be problem with sb_fdblocks count but kernel really look for
features2 and behaves differently if lazy-count is sets on right place.


jan


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