tmpfs: Allow update mounts only for certain options.

Since r230208 update mounts were allowed if the list of mount options
contained the "export" option. This is not correct as tmpfs doesn't
really support updating all options.

Reviewed by:	kevlo, trociny

2 files changed, 15 insertions, 6 deletions

diff --git a/sys/fs/tmpfs/tmpfs.h b/sys/fs/tmpfs/tmpfs.h
index fad97ac..1c6d714 100644
--- a/sys/fs/tmpfs/tmpfs.h
+++ b/sys/fs/tmpfs/tmpfs.h
@@ -387,6 +387,9 @@ struct tmpfs_mount {
 	 * tmpfs_pool.c. */
 	uma_zone_t		tm_dirent_pool;
 	uma_zone_t		tm_node_pool;
+
+	/* Read-only status. */
+	int			tm_ronly;
 };
 #define TMPFS_LOCK(tm) mtx_lock(&(tm)->allnode_lock)
 #define TMPFS_UNLOCK(tm) mtx_unlock(&(tm)->allnode_lock)
diff --git a/sys/fs/tmpfs/tmpfs_vfsops.c b/sys/fs/tmpfs/tmpfs_vfsops.c
index 96d7321..a08dafa 100644
--- a/sys/fs/tmpfs/tmpfs_vfsops.c
+++ b/sys/fs/tmpfs/tmpfs_vfsops.c
@@ -82,6 +82,10 @@ static const char *tmpfs_opts[] = {
 	NULL
 };
 
+static const char *tmpfs_updateopts[] = {
+	"from", "export", NULL
+};
+
 /* --------------------------------------------------------------------- */
 
 static int
@@ -150,12 +154,13 @@ tmpfs_mount(struct mount *mp)
 		return (EINVAL);
 
 	if (mp->mnt_flag & MNT_UPDATE) {
-		/*
-		 * Only support update mounts for NFS export.
-		 */
-		if (vfs_flagopt(mp->mnt_optnew, "export", NULL, 0))
-			return (0);
-		return (EOPNOTSUPP);
+		/* Only support update mounts for certain options. */
+		if (vfs_filteropt(mp->mnt_optnew, tmpfs_updateopts) != 0)
+			return (EOPNOTSUPP);
+		if (vfs_flagopt(mp->mnt_optnew, "ro", NULL, 0) !=
+		    ((struct tmpfs_mount *)mp->mnt_data)->tm_ronly)
+			return (EOPNOTSUPP);
+		return (0);
 	}
 
 	vn_lock(mp->mnt_vnodecovered, LK_SHARED | LK_RETRY);
@@ -228,6 +233,7 @@ tmpfs_mount(struct mount *mp)
 	    tmpfs_node_ctor, tmpfs_node_dtor,
 	    tmpfs_node_init, tmpfs_node_fini,
 	    UMA_ALIGN_PTR, 0);
+	tmp->tm_ronly = (mp->mnt_flag & MNT_RDONLY) != 0;
 
 	/* Allocate the root node. */
 	error = tmpfs_alloc_node(tmp, VDIR, root_uid,