In the new order of things dictated by nmount(2), a read-only mount

is to be requested via a "ro" option.  At the same time, MNT_RDONLY
is gradually becoming an indicator of the current state of the FS
instead of a command flag.  Today passing MNT_RDONLY alone to the
kernel's mount machinery will lead to various glitches.  (See the
PRs for examples.)

Therefore mount the root FS with a "ro" option instead of the
MNT_RDONLY flag.  (Note that MNT_RDONLY still is added to the mount
flags internally, by vfs_donmount(), if "ro" was specified.)

To be able to pass "ro" cleanly to kernel_vmount(), teach the latter
function to accept options with NULL values.

Also correct the comment explaining how mount_arg() handles length
of -1.

PR:		bin/106636 kern/120319
Submitted by:	Jaakko Heinonen <see PR kern/120319 for email> (originally)

1 files changed, 4 insertions, 3 deletions

diff --git a/sys/kern/vfs_mount.c b/sys/kern/vfs_mount.c
index 146f868..1f66a07 100644
--- a/sys/kern/vfs_mount.c
+++ b/sys/kern/vfs_mount.c
@@ -1723,10 +1723,11 @@ vfs_mountroot_try(const char *mountfrom)
 		strcpy(path, ROOTNAME);
 
 	error = kernel_vmount(
-	    MNT_RDONLY | MNT_ROOTFS,
+	    MNT_ROOTFS,
 	    "fstype", vfsname,
 	    "fspath", "/",
 	    "from", path,
+	    "ro", NULL,
 	    NULL);
 	if (error == 0) {
 		/*
@@ -2213,7 +2214,7 @@ mount_argsu(struct mntarg *ma, const char *name, const void *val, int len)
 /*
  * Plain argument.
  *
- * If length is -1, use printf.
+ * If length is -1, treat value as a C string.
  */
 struct mntarg *
 mount_arg(struct mntarg *ma, const char *name, const void *val, int len)
@@ -2300,7 +2301,7 @@ kernel_vmount(int flags, ...)
 		if (cp == NULL)
 			break;
 		vp = va_arg(ap, const void *);
-		ma = mount_arg(ma, cp, vp, -1);
+		ma = mount_arg(ma, cp, vp, (vp != NULL ? -1 : 0));
 	}
 	va_end(ap);