From 47ae32d6a54955a041cdc30b06d0bb16e75f68d5 Mon Sep 17 00:00:00 2001
From: Valerie Henson <val_henson@linux.intel.com>
Date: Wed, 13 Dec 2006 00:34:34 -0800
Subject: [PATCH] relative atime

Add "relatime" (relative atime) support.  Relative atime only updates the
atime if the previous atime is older than the mtime or ctime.  Like
noatime, but useful for applications like mutt that need to know when a
file has been read since it was last modified.

A corresponding patch against mount(8) is available at
http://userweb.kernel.org/~akpm/mount-relative-atime.txt

Signed-off-by: Valerie Henson <val_henson@linux.intel.com>
Cc: Mark Fasheh <mark.fasheh@oracle.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Karel Zak <kzak@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/fs/inode.c b/fs/inode.c
index 04536eb..bf21dc6 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1177,13 +1177,27 @@ void touch_atime(struct vfsmount *mnt, struct dentry *dentry)
 			return;
 		if ((mnt->mnt_flags & MNT_NODIRATIME) && S_ISDIR(inode->i_mode))
 			return;
+
+		if (mnt->mnt_flags & MNT_RELATIME) {
+			/*
+			 * With relative atime, only update atime if the
+			 * previous atime is earlier than either the ctime or
+			 * mtime.
+			 */
+			if (timespec_compare(&inode->i_mtime,
+						&inode->i_atime) < 0 &&
+			    timespec_compare(&inode->i_ctime,
+						&inode->i_atime) < 0)
+				return;
+		}
 	}
 
 	now = current_fs_time(inode->i_sb);
-	if (!timespec_equal(&inode->i_atime, &now)) {
-		inode->i_atime = now;
-		mark_inode_dirty_sync(inode);
-	}
+	if (timespec_equal(&inode->i_atime, &now))
+		return;
+
+	inode->i_atime = now;
+	mark_inode_dirty_sync(inode);
 }
 EXPORT_SYMBOL(touch_atime);
 
diff --git a/fs/namespace.c b/fs/namespace.c
index fde8553..5ef336c 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -368,6 +368,7 @@ static int show_vfsmnt(struct seq_file *m, void *v)
 		{ MNT_NOEXEC, ",noexec" },
 		{ MNT_NOATIME, ",noatime" },
 		{ MNT_NODIRATIME, ",nodiratime" },
+		{ MNT_RELATIME, ",relatime" },
 		{ 0, NULL }
 	};
 	struct proc_fs_info *fs_infop;
@@ -1405,9 +1406,11 @@ long do_mount(char *dev_name, char *dir_name, char *type_page,
 		mnt_flags |= MNT_NOATIME;
 	if (flags & MS_NODIRATIME)
 		mnt_flags |= MNT_NODIRATIME;
+	if (flags & MS_RELATIME)
+		mnt_flags |= MNT_RELATIME;
 
 	flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
-		   MS_NOATIME | MS_NODIRATIME);
+		   MS_NOATIME | MS_NODIRATIME | MS_RELATIME);
 
 	/* ... and get the mountpoint */
 	retval = path_lookup(dir_name, LOOKUP_FOLLOW, &nd);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index adce6e1..186da81 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -120,6 +120,7 @@ extern int dir_notify_enable;
 #define MS_PRIVATE	(1<<18)	/* change to private */
 #define MS_SLAVE	(1<<19)	/* change to slave */
 #define MS_SHARED	(1<<20)	/* change to shared */
+#define MS_RELATIME	(1<<21)	/* Update atime relative to mtime/ctime. */
 #define MS_ACTIVE	(1<<30)
 #define MS_NOUSER	(1<<31)
 
diff --git a/include/linux/mount.h b/include/linux/mount.h
index e357dc8..1b7e178 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -27,6 +27,7 @@ struct mnt_namespace;
 #define MNT_NOEXEC	0x04
 #define MNT_NOATIME	0x08
 #define MNT_NODIRATIME	0x10
+#define MNT_RELATIME	0x20
 
 #define MNT_SHRINKABLE	0x100
 
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