[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>

4 files changed, 24 insertions, 5 deletions

diff --git a/fs/inode.c b/fs/inode.c
index 04536ebc5ac4..bf21dc6d0dbd 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 fde8553faa76..5ef336c1103c 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 adce6e1d70c2..186da813541e 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 e357dc86a4de..1b7e178b0d84 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