Export the name of the device used to mount the root file system as

kern.rootdev.  If rootdev is undefined (NFS mount, etc), export an
empty string.

Desired by:	peter

1 files changed, 24 insertions, 0 deletions

diff --git a/sys/kern/vfs_mount.c b/sys/kern/vfs_mount.c
index 9c47ceb..a7efa34 100644
--- a/sys/kern/vfs_mount.c
+++ b/sys/kern/vfs_mount.c
@@ -150,6 +150,30 @@ char		*rootdevnames[2] = {NULL, NULL};
 static int	setrootbyname(char *name);
 dev_t		rootdev = NODEV;
 
+/*
+ * Has to be dynamic as the value of rootdev can change; however, it can't
+ * change after the root is mounted, so a user process can't access this
+ * sysctl until after the value is unchangeable.
+ */
+static int
+sysctl_rootdev(SYSCTL_HANDLER_ARGS)
+{
+	int error;
+
+	/* _RD prevents this from happening. */
+	KASSERT(req->newptr == NULL, ("Attempt to change root device name"));
+
+	if (rootdev != NODEV)
+		error = sysctl_handle_string(oidp, rootdev->si_name, 0, req);
+	else
+		error = sysctl_handle_string(oidp, "", 0, req);
+
+	return (error);
+}
+
+SYSCTL_PROC(_kern, OID_AUTO, rootdev, CTLTYPE_STRING | CTLFLAG_RD,
+    0, 0, sysctl_rootdev, "A", "Root file system device");
+
 /* Remove one mount option. */
 static void
 vfs_freeopt(struct vfsoptlist *opts, struct vfsopt *opt)