linux-kernel - Re: [EXT4 set 4][PATCH 1/5] i

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Message-Id: <20070710233529.7d8bfe9a.akpm@linux-foundation.org>
Date:	Tue, 10 Jul 2007 23:35:29 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	cmm@...ibm.com
Cc:	Neil Brown <neilb@...e.de>, 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 1/5] i_version:64 bit inode version

On Tue, 10 Jul 2007 23:18:50 -0400 Mingming Cao <cmm@...ibm.com> wrote:

> On Tue, 2007-07-10 at 22:17 -0700, Andrew Morton wrote:
> > On Tue, 10 Jul 2007 22:09:08 -0400 Mingming Cao <cmm@...ibm.com> wrote:
> > 
> > > David Chinneer pointed that we need to journal the version number
> > > updates together with the operations that causes the change of the inode
> > > version number, in order to survive server crashes so clients won't see
> > > the counter go backwards.
> > > 
> > > So increment i_version in fs code is probably the place to ensure the
> > > inode version changes are stored to disk. It's seems update the ext4
> > > inode version in every ext4_mark_inode_dirty() is the easiest way.
> > 
> > That still makes us dependent upon _something_ changing the inode.  For
> > overwrites the only something is mtime.
> > 
> > If we don't want to have a peculiar dependency upon s_time_gran=1e9 (and
> > I don't think we do) then I guess we'll need new code in or around
> > file_update_time() to do this.
> 
> do you mean mark inode dirty all the times in file_update_time()? Not
> sure about the overhead for ext3/4.
> 

hm, I hadn't thought about it in any detail.

Maybe something like

--- a/fs/inode.c~a
+++ a/fs/inode.c
@@ -1238,6 +1238,11 @@ void file_update_time(struct file *file)
 		sync_it = 1;
 	}
 
+	if (IS_I_VERSION_64(inode)) {
+		inode_inc_iversion(inode);	/* Takes i_lock on 32-bit */
+		sync_it = 1;
+	}
+
 	if (sync_it)
 		mark_inode_dirty_sync(inode);
 }
_

?
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