Implement relative atime mount flag. Relative atime means the operator

wants atime be maintained only when it's older than creation and
modification time.

For now this only applies to UFS and ext2fs cases.

Usage:

	mount -o relatime <special> <mountpoint>

lib/libc/sys/statfs.2

@@ -142,6 +142,9 @@ Identifies the root file system.
 The file system is exported read-only.
 .It Dv MNT_NOATIME
 Updating of file access times is disabled.
+.It Dv MNT_RELATIME
+Updating of file access times is only done when it is smaller than both creation
+and modification times.
 .It Dv MNT_USER
 The file system has been mounted by a user.
 .\".It Dv MNT_IGNORE

sbin/mount/mount.8

@@ -222,6 +222,10 @@ is useful on file systems where there are large numbers of files and
 performance is more critical than updating the file access time (which is
 rarely ever important).
 This option is currently only supported on local file systems.
+.It Cm relatime
+Do not update the file access time when reading from a file, if the access
+time is already later than both file creation time and file modification
+times.
 .It Cm noauto
 This file system should be skipped when
 .Nm

sbin/mount/mount.c

@@ -97,6 +97,7 @@ static struct opt {
 	{ MNT_ASYNC,		"asynchronous" },
 	{ MNT_EXPORTED,		"NFS exported" },
 	{ MNT_LOCAL,		"local" },
+	{ MNT_RELATIME,		"relative atime" },
 	{ MNT_NOATIME,		"noatime" },
 	{ MNT_NOEXEC,		"noexec" },
 	{ MNT_NOSUID,		"nosuid" },

sys/fs/ext2fs/ext2_vnops.c

@@ -1697,7 +1697,15 @@ ext2_read(struct vop_read_args *ap)
 	}
 
 	if ((error == 0 || uio->uio_resid != orig_resid) &&
-	    (vp->v_mount->mnt_flag & MNT_NOATIME) == 0)
+	    (vp->v_mount->mnt_flag & MNT_NOATIME) == 0 &&
+	    (ip->i_flag & IN_ACCESS) == 0 &&
+	    ((vp->v_mount->mnt_flag & MNT_RELATIME) == 0 ||
+	    (ip->i_mtime == ip->i_atime ?
+	     ip->i_mtimensec >= ip->i_atimensec :
+	     ip->i_mtime >= ip->i_atime) ||
+	    (ip->i_ctime == ip->i_atime ?
+	     ip->i_ctimensec >= ip->i_atimensec :
+	     ip->i_ctime >= ip->i_atime)))
 		ip->i_flag |= IN_ACCESS;
 	return (error);
 }

sys/kern/vfs_mount.c

@@ -99,6 +99,7 @@ static const char *global_opts[] = {
 	"rw",
 	"nosuid",
 	"noexec",
+	"relatime",
 	NULL
 };
 
@@ -602,6 +603,14 @@ vfs_donmount(struct thread *td, uint64_t fsflags, struct uio *fsoptions)
 			free(opt->name, M_MOUNT);
 			opt->name = strdup("nonoatime", M_MOUNT);
 		}
+		else if (strcmp(opt->name, "norelatime") == 0) {
+			vfs_freeopt(optlist, opt);
+			fsflags &= ~MNT_RELATIME;
+		}
+		else if (strcmp(opt->name, "relatime") == 0) {
+			vfs_freeopt(optlist, opt);
+			fsflags |= MNT_RELATIME;
+		}
 		else if (strcmp(opt->name, "noclusterr") == 0)
 			fsflags |= MNT_NOCLUSTERR;
 		else if (strcmp(opt->name, "clusterr") == 0) {
@@ -811,7 +820,7 @@ vfs_domount_first(
 	/* XXXMAC: pass to vfs_mount_alloc? */
 	mp->mnt_optnew = *optlist;
 	/* Set the mount level flags. */
-	mp->mnt_flag = (fsflags & (MNT_UPDATEMASK | MNT_ROOTFS | MNT_RDONLY));
+	mp->mnt_flag = (fsflags & (MNT_UPDATEMASK | MNT_ROOTFS | MNT_RDONLY | MNT_RELATIME));
 
 	/*
 	 * Mount the filesystem.
@@ -933,7 +942,8 @@ vfs_domount_update(
 	MNT_ILOCK(mp);
 	mp->mnt_flag &= ~MNT_UPDATEMASK;
 	mp->mnt_flag |= fsflags & (MNT_RELOAD | MNT_FORCE | MNT_UPDATE |
-	    MNT_SNAPSHOT | MNT_ROOTFS | MNT_UPDATEMASK | MNT_RDONLY);
+	    MNT_SNAPSHOT | MNT_ROOTFS | MNT_UPDATEMASK | MNT_RDONLY |
+	    MNT_RELATIME);
 	if ((mp->mnt_flag & MNT_ASYNC) == 0)
 		mp->mnt_kern_flag &= ~MNTK_ASYNC;
 	MNT_IUNLOCK(mp);

sys/kern/vfs_subr.c

@@ -3004,6 +3004,7 @@ DB_SHOW_COMMAND(mount, db_show_mount)
 	MNT_FLAG(MNT_GJOURNAL);
 	MNT_FLAG(MNT_MULTILABEL);
 	MNT_FLAG(MNT_ACLS);
+	MNT_FLAG(MNT_RELATIME);
 	MNT_FLAG(MNT_NOATIME);
 	MNT_FLAG(MNT_NOCLUSTERR);
 	MNT_FLAG(MNT_NOCLUSTERW);
@@ -4526,11 +4527,33 @@ void
 vfs_mark_atime(struct vnode *vp, struct ucred *cred)
 {
 	struct mount *mp;
+	struct vattr vattr;
 
 	mp = vp->v_mount;
 	ASSERT_VOP_LOCKED(vp, "vfs_mark_atime");
-	if (mp != NULL && (mp->mnt_flag & (MNT_NOATIME | MNT_RDONLY)) == 0)
-		(void)VOP_MARKATIME(vp);
+
+	/*
+	 * Do nothing if the file system is mounted with noatime or
+	 * marked as read only.
+	 */
+	if (mp == NULL || (mp->mnt_flag & (MNT_NOATIME | MNT_RDONLY)) != 0)
+		return;
+
+	/*
+	 * Relative atime: do nothing if both ctime and mtime are
+	 * smaller than atime.
+	 */
+	if ((mp->mnt_flag & MNT_RELATIME) == MNT_RELATIME) {
+		if (VOP_GETATTR(vp, &vattr, cred) != 0)
+			return;
+		else {
+			if (timespeccmp(&vattr.va_mtime, &vattr.va_atime, < ) &&
+			    timespeccmp(&vattr.va_ctime, &vattr.va_atime, < ))
+				return;
+		}
+	}
+
+	(void)VOP_MARKATIME(vp);
 }
 
 /*

sys/sys/mount.h

@@ -259,6 +259,7 @@ void          __mnt_vnode_markerfree_active(struct vnode **mvp, struct mount *);
 #define	MNT_NOCLUSTERR	0x0000000040000000ULL /* disable cluster read */
 #define	MNT_NOCLUSTERW	0x0000000080000000ULL /* disable cluster write */
 #define	MNT_SUJ		0x0000000100000000ULL /* using journaled soft updates */
+#define	MNT_RELATIME	0x0000000200000000ULL /* using relative atime */
 
 /*
  * NFS export related mount flags.
@@ -295,7 +296,7 @@ void          __mnt_vnode_markerfree_active(struct vnode **mvp, struct mount *);
 			MNT_NOCLUSTERW	| MNT_SUIDDIR	| MNT_SOFTDEP	| \
 			MNT_IGNORE	| MNT_EXPUBLIC	| MNT_NOSYMFOLLOW | \
 			MNT_GJOURNAL	| MNT_MULTILABEL | MNT_ACLS	| \
-			MNT_NFS4ACLS)
+			MNT_NFS4ACLS	| MNT_RELATIME)
 
 /* Mask of flags that can be updated. */
 #define	MNT_UPDATEMASK (MNT_NOSUID	| MNT_NOEXEC	| \

sys/ufs/ffs/ffs_vnops.c

@@ -621,7 +621,14 @@ ffs_read(ap)
 
 	if ((error == 0 || uio->uio_resid != orig_resid) &&
 	    (vp->v_mount->mnt_flag & MNT_NOATIME) == 0 &&
-	    (ip->i_flag & IN_ACCESS) == 0) {
+	    (ip->i_flag & IN_ACCESS) == 0 &&
+	    ((vp->v_mount->mnt_flag & MNT_RELATIME) == 0 ||
+	    (DIP(ip, i_mtime) == DIP(ip, i_atime) ?
+	    (DIP(ip, i_mtimensec) >= DIP(ip, i_atimensec)) :
+	    (DIP(ip, i_mtime) >= DIP(ip, i_atime))) ||
+	    (DIP(ip, i_ctime) == DIP(ip, i_atime) ?
+	    (DIP(ip, i_ctimensec) >= DIP(ip, i_atimensec)) :
+	    (DIP(ip, i_ctime) >= DIP(ip, i_atime))))) {
 		VI_LOCK(vp);
 		ip->i_flag |= IN_ACCESS;
 		VI_UNLOCK(vp);