linux-kernel - Re: [EXT4 set 4][PATCH 3/5] i_version:ext4 inode version read/store

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Date:	Wed, 11 Jul 2007 05:50:13 -0600
From:	Andreas Dilger <adilger@...sterfs.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	cmm@...ibm.com, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org,
	nfsv4@...ux-nfs.org
Subject: Re: [EXT4 set 4][PATCH 3/5] i_version:ext4 inode version read/store

On Jul 10, 2007  16:31 -0700, Andrew Morton wrote:
> > This patch adds 64-bit inode version support to ext4. The lower 32 bits
> > are stored in the osd1.linux1.l_i_version field while the high 32 bits
> > are stored in the i_version_hi field newly created in the ext4_inode.
> 
> So reading the code here does serve to answer the question I raised against
> the earlier patch.  A bit.
> 
> I'd have thought that this patch and the one which adds i_version_hi should
> be folded into a single diff?

It could be - the original patch to reserve i_version_hi was submitted to
before the patches were ready to avoid that space being used by something
else.

> > +	if (EXT4_INODE_SIZE(inode->i_sb) > EXT4_GOOD_OLD_INODE_SIZE) {
> > +		if (EXT4_FITS_IN_INODE(raw_inode, ei, i_version_hi))
> > +			inode->i_version |=
> > +			(__u64)(le32_to_cpu(raw_inode->i_version_hi)) << 32;
> 
> <checks the precedence of "(type)" versus "<<">
> 
> <OK>
> 
> > +	}
> 
> I don't quite see how the above two tests are sufficient to unambiguously
> determine that the i_version_hi field is present on-disk.
> 
> I guess we're implicitly assuming that if the on-disk inode is big enough
> then it _must_ have i_version_hi in there?  If so, why is the comparison
> with EXT4_GOOD_OLD_INODE_SIZE needed?

The GOOT_OLD_INODE_SIZE check is needed to know if i_extra_isize is even
present or valid in the on-disk inode.

> > @@ -2852,8 +2859,14 @@ static int ext4_do_update_inode(handle_t
> > +	raw_inode->i_disk_version = cpu_to_le32(inode->i_version);
> > +	if (ei->i_extra_isize) {
> > +		if (EXT4_FITS_IN_INODE(raw_inode, ei, i_version_hi)) {
> 
> There's no comparison with EXT4_GOOD_OLD_INODE_SIZE here...

Because this is the in-memory version and it is always valid (set to zero
if there is extra space in the on-disk inode).

Cheers, Andreas
--
Andreas Dilger
Principal Software Engineer
Cluster File Systems, Inc.

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