For a mounted file system which is read-only, when

doing the MNT_RELOAD, pass in "ro" and "update"
string mount options to nmount() instead of MNT_RDONLY and MNT_UPDATE flags.

Due to the complexity of the mount parsing code especially
with respect to the root file system, passing in MNT_RDONLY and MNT_UPDATE
flags would do weird things and would cause fsck to convert the root
file system from a read-only mount to read-write.

To test:
 - boot into single user mode
 - show mounted file systems with: mount
 - root file system should be mounted read-only
 - fsck /
 - show mounted file systems with: mount
 - root file system should still be mounted read-only

PR:		120319
MFC after:	1 month
Reported by:	yar

1 files changed, 3 insertions, 1 deletions

diff --git a/sbin/fsck_ffs/main.c b/sbin/fsck_ffs/main.c
index 04c313c..1e6f370 100644
--- a/sbin/fsck_ffs/main.c
+++ b/sbin/fsck_ffs/main.c
@@ -532,7 +532,7 @@ chkdoreload(struct statfs *mntp)
 	 * as safely as possible.
 	 */
 	if (mntp->f_flags & MNT_RDONLY) {
-		fflags = fflags | MNT_UPDATE | MNT_RELOAD;
+		fflags = fflags | MNT_RELOAD;
 		build_iovec(&iov, &iovlen, "fstype", "ffs", 4);
 		build_iovec(&iov, &iovlen, "from", mntp->f_mntfromname,
 		    (size_t)-1);
@@ -540,6 +540,8 @@ chkdoreload(struct statfs *mntp)
 		    (size_t)-1);
 		build_iovec(&iov, &iovlen, "errmsg", errmsg,
 		    sizeof(errmsg));
+		build_iovec(&iov, &iovlen, "update", NULL, 0);
+		build_iovec(&iov, &iovlen, "ro", NULL, 0);
 		if (nmount(iov, iovlen, fflags) == 0) {
 			return (0);
 		}