[RFC] [patch 3/3] i_version update for ext4: user interface

[RFC] [patch 3/3] i_version update for ext4: user interface

[Cordenner jean noel]

This patch adds a  ``st_i_version'' field in the stat
structure, and modifies the stat(2) syscall accordingly. Currently the
change is only visible on i386 and x86_64 archs.



Signed-off-by: Jean Noel Cordenner <jean-noel.cordenner@bull.net>

Index: linux-2.6.20-rc5/fs/stat.c
===================================================================
--- linux-2.6.20-rc5.orig/fs/stat.c     2007-01-19 16:59:15.000000000 +0100
+++ linux-2.6.20-rc5/fs/stat.c  2007-01-23 16:21:17.000000000 +0100
@@ -31,6 +31,7 @@
         stat->atime = inode->i_atime;
         stat->mtime = inode->i_mtime;
         stat->ctime = inode->i_ctime;
+       stat->i_version = inode->i_version;
         stat->size = i_size_read(inode);
         stat->blocks = inode->i_blocks;
         stat->blksize = (1 << inode->i_blkbits);
@@ -226,6 +227,7 @@
         tmp.st_atime = stat->atime.tv_sec;
         tmp.st_mtime = stat->mtime.tv_sec;
         tmp.st_ctime = stat->ctime.tv_sec;
+       tmp.st_i_version = stat->i_version;
  #ifdef STAT_HAVE_NSEC
         tmp.st_atime_nsec = stat->atime.tv_nsec;
         tmp.st_mtime_nsec = stat->mtime.tv_nsec;
@@ -359,6 +361,7 @@
         tmp.st_mtime_nsec = stat->mtime.tv_nsec;
         tmp.st_ctime = stat->ctime.tv_sec;
         tmp.st_ctime_nsec = stat->ctime.tv_nsec;
+       tmp.st_i_version = stat->i_version;
         tmp.st_size = stat->size;
         tmp.st_blocks = stat->blocks;
         tmp.st_blksize = stat->blksize;
Index: linux-2.6.20-rc5/include/linux/stat.h
===================================================================
--- linux-2.6.20-rc5.orig/include/linux/stat.h  2006-11-29 
22:57:37.000000000 +0100
+++ linux-2.6.20-rc5/include/linux/stat.h       2007-01-23 
16:22:18.000000000 +0100
@@ -68,6 +68,7 @@
         struct timespec  atime;
         struct timespec mtime;
         struct timespec ctime;
+       unsigned long   i_version;
         unsigned long   blksize;
         unsigned long long      blocks;
  };
Index: linux-2.6.20-rc5/include/asm-i386/stat.h
===================================================================
--- linux-2.6.20-rc5.orig/include/asm-i386/stat.h       2006-11-29 
22:57:37.000000000 +0100
+++ linux-2.6.20-rc5/include/asm-i386/stat.h    2007-01-23 
17:48:36.000000000 +0100
@@ -32,7 +32,7 @@
         unsigned long  st_mtime_nsec;
         unsigned long  st_ctime;
         unsigned long  st_ctime_nsec;
-       unsigned long  __unused4;
+       unsigned long  st_i_version;
         unsigned long  __unused5;
  };

@@ -41,7 +41,7 @@
   */
  struct stat64 {
         unsigned long long      st_dev;
-       unsigned char   __pad0[4];
+       unsigned int    st_i_version;

  #define STAT64_HAS_BROKEN_ST_INO       1
         unsigned long   __st_ino;
Index: linux-2.6.20-rc5/include/asm-x86_64/stat.h
===================================================================
--- linux-2.6.20-rc5.orig/include/asm-x86_64/stat.h     2006-11-29 
22:57:37.000000000 +0100
+++ linux-2.6.20-rc5/include/asm-x86_64/stat.h  2007-01-23 
17:57:03.000000000 +0100
@@ -23,7 +23,8 @@
         unsigned long   st_mtime_nsec;
         unsigned long   st_ctime;
         unsigned long   st_ctime_nsec;
-       long            __unused[3];
+       unsigned long   st_i_version;
+       long            __unused[2];
  };

  /* For 32bit emulation */

Re: [RFC] [patch 3/3] i_version update for ext4: user interface

[Andreas Dilger]

On Jan 23, 2007  18:24 +0100, Cordenner jean noel wrote:
> This patch adds a  ``st_i_version'' field in the stat
> structure, and modifies the stat(2) syscall accordingly. Currently the
> change is only visible on i386 and x86_64 archs.

What is the need for exporting i_version to userspace?

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

Re: [RFC] [patch 3/3] i_version update for ext4: user interface

[J. Bruce Fields]

On Tue, Jan 23, 2007 at 11:52:08AM -0700, Andreas Dilger wrote:
> On Jan 23, 2007  18:24 +0100, Cordenner jean noel wrote:
> > This patch adds a  ``st_i_version'' field in the stat
> > structure, and modifies the stat(2) syscall accordingly. Currently the
> > change is only visible on i386 and x86_64 archs.
> 
> What is the need for exporting i_version to userspace?

Maybe none, but it seems potentially really useful to me; in practice
aren't most uses of mtime/ctime exactly in order to find out if the file
has changed recently?

Who else is asking for finer time resolutions?  Is it because they need
the precision (or the inter-file comparison) or because they need to
know whether a file has changed?

Isn't anybody that currently maintains some cached information about a
filesystem currently living with the same races as NFS?

--b.

Re: [RFC] [patch 3/3] i_version update for ext4: user interface

[Peter Staubach]

J. Bruce Fields wrote:
> On Tue, Jan 23, 2007 at 11:52:08AM -0700, Andreas Dilger wrote:
>   
>> On Jan 23, 2007  18:24 +0100, Cordenner jean noel wrote:
>>     
>>> This patch adds a  ``st_i_version'' field in the stat
>>> structure, and modifies the stat(2) syscall accordingly. Currently the
>>> change is only visible on i386 and x86_64 archs.
>>>       
>> What is the need for exporting i_version to userspace?
>>     
>
> Maybe none, but it seems potentially really useful to me; in practice
> aren't most uses of mtime/ctime exactly in order to find out if the file
> has changed recently?
>
> Who else is asking for finer time resolutions?  Is it because they need
> the precision (or the inter-file comparison) or because they need to
> know whether a file has changed?
>
> Isn't anybody that currently maintains some cached information about a
> filesystem currently living with the same races as NFS?

Doesn't the BSD stat struct have a field like this?  If so, perhaps
they can remember why it was deemed to be interesting?

    Thanx...

       ps