linux-ext4 - Re: [RFC] [patch 2/2] i_version update

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Message-Id: <1179180669.3772.20.camel@dyn9047017103.beaverton.ibm.com>
Date:	Mon, 14 May 2007 15:11:09 -0700
From:	Mingming Cao <cmm@...ibm.com>
To:	Andreas Dilger <adilger@...sterfs.com>
Cc:	Cordenner jean noel <jean-noel.cordenner@...l.net>,
	linux-ext4@...r.kernel.org, Kalpak Shah <kalpak@...sterfs.com>
Subject: Re: [RFC] [patch 2/2] i_version update - ext4 part

On Mon, 2007-05-14 at 14:31 -0600, Andreas Dilger wrote:
> On May 14, 2007  14:21 -0600, Andreas Dilger wrote:
> > On May 14, 2007  13:05 +0200, Cordenner jean noel wrote:
> > > @@ -331,12 +331,13 @@
> > >  	} osd2;				/* OS dependent 2 */
> > >  	__le16	i_extra_isize;
> > >  	__le16	i_pad1;
> > > +	__le32	i_disk_version_hi;
> > 
> > No, this is not correct.  There are already several other fields here
> > (nanosecond ctime, mtime, atime, crtime (creation time)) so you need
> > to use the correct reserved field for this.
> > 
> > 	__u16	i_extra_isize;
> > 	__u16	i_pad1;
> > 	__u32	i_ctime_extra;	/* extra Change time (nsec << 2 | epoch) */
> > 	__u32	i_mtime_extra;	/* extra Modification time (nsec << 2 | epoch)*/
> > 	__u32	i_atime_extra;	/* extra Access time (nsec << 2 | epoch) */
> > 	__u32	i_crtime;	/* File creation time */
> > 	__u32	i_crtime_extra;	/* extra File creation time (nsec << 2 |epoch)*/
> 
> Sorry, I meant to add (before hitting send :-) that the field after
> i_crtime_extra is supposed to be "i_disk_version_hi".
> 


> See the patch from Kalpak Shah "[RFC] 64-bit inode version" which also handles
> the case for expanding i_extra_isize to cover the needed extra fields if
> i_extra_isize is not large enough.  That patch didn't include the 64-bit
> i_version_hi yet, because there wasn't yet agreement at that time if
> the iversion_hi should be allocated separately, but that was since decided.
> 

Kalpak already sent a patch [PATCH] Add i_version_hi for 64-bit version,
which added i_version_hi after i_crtime. His patch has in ext4 git tree
for a while.

ftp://ftp.kernel.org/pub/linux/kernel/people/tytso/ext4-patches/2.6.21-
ext4-1

Regards,
Mingming

> Without that patch, your patch will possibly corrupt the extended attributes
> by just overwriting i_disk_version_hi while ignoring the actual value of
> i_extra_isize.  This would clobber the EA magic and result in loss of all
> EAs in that inode.
> 
> Cheers, Andreas
> --
> Andreas Dilger
> Principal Software Engineer
> Cluster File Systems, Inc.
> 
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