Add a strictatime mount option

Add support for explicitly requesting full atime updates. This makes it
possible for kernels to default to relatime but still allow userspace to
override it.

Signed-off-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 7 insertions, 1 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 06f8e63f6cb1..d0659ec291c9 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -780,6 +780,7 @@ static void show_mnt_opts(struct seq_file *m, struct vfsmount *mnt)
                 { MNT_NOATIME, ",noatime" },
                 { MNT_NODIRATIME, ",nodiratime" },
                 { MNT_RELATIME, ",relatime" },
+                { MNT_STRICTATIME, ",strictatime" },
                 { 0, NULL }
         };
         const struct proc_fs_info *fs_infop;
@@ -1932,11 +1933,14 @@ long do_mount(char *dev_name, char *dir_name, char *type_page,
                 mnt_flags |= MNT_NODIRATIME;
         if (flags & MS_RELATIME)
                 mnt_flags |= MNT_RELATIME;
+        if (flags & MS_STRICTATIME)
+                mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME);
         if (flags & MS_RDONLY)
                 mnt_flags |= MNT_READONLY;
 
         flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
-                   MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT);
+                   MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT |
+                   MS_STRICTATIME);
 
         /* ... and get the mountpoint */
         retval = kern_path(dir_name, LOOKUP_FOLLOW, &path);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 92734c0012e6..5bc81c4a98c1 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -141,6 +141,7 @@ struct inodes_stat_t {
 #define MS_RELATIME     (1<<21) /* Update atime relative to mtime/ctime. */
 #define MS_KERNMOUNT    (1<<22) /* this is a kern_mount call */
 #define MS_I_VERSION    (1<<23) /* Update inode I_version field */
+#define MS_STRICTATIME  (1<<24) /* Always perform atime updates */
 #define MS_ACTIVE       (1<<30)
 #define MS_NOUSER       (1<<31)
 
diff --git a/include/linux/mount.h b/include/linux/mount.h
index cab2a85e2ee8..51f55f903aff 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -27,6 +27,7 @@ struct mnt_namespace;
 #define MNT_NODIRATIME  0x10
 #define MNT_RELATIME    0x20
 #define MNT_READONLY    0x40    /* does the user want this to be r/o? */
+#define MNT_STRICTATIME 0x80
 
 #define MNT_SHRINKABLE  0x100
 #define MNT_IMBALANCED_WRITE_COUNT      0x200 /* just for debugging */