In the bootblocks, after discovering and opening /bsd.upgrade, fchmod -x

so the file cannot be re-executed upon the next boot.  This provides a
stronger one-shot-upgrade model than the upgrade script's rm /bsd.upgrade.
Now various forms of upgrade failure will reboot into /bsd, which is probably
more recoverable.  Performing fchmod -x depends on (1) use of MI boot.c
(not alpha/macppc/sparc64/sgi/octeon) and (2) "can write blocks" functionality
in the IO layer.  Most architectures have this support now.

Two diagnostics "fchmod a-x %s: failed" and "/bsd.upgrade is not u+x" will
remain in the tree while refinements happen for some of the laggard
architectures.

based upon a discussion florian
tested in snapshots for more than a week without any complaints

1 files changed, 59 insertions, 0 deletions

diff --git a/sys/lib/libsa/fchmod.c b/sys/lib/libsa/fchmod.c
new file mode 100644
index 00000000000..7d9bc9cac36
--- /dev/null
+++ b/sys/lib/libsa/fchmod.c
@@ -0,0 +1,59 @@
+/*	$OpenBSD: fchmod.c,v 1.1 2019/08/03 15:22:17 deraadt Exp $	*/
+/*	$NetBSD: stat.c,v 1.3 1994/10/26 05:45:07 cgd Exp $	*/
+
+/*-
+ * Copyright (c) 1993
+ *	The Regents of the University of California.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ *	@(#)stat.c	8.1 (Berkeley) 6/11/93
+ */
+
+#include "stand.h"
+
+int
+fchmod(int fd, mode_t m)
+{
+	struct open_file *f = &files[fd];
+
+	if (f->f_ops->fchmod == NULL) {
+		errno = EOPNOTSUPP;
+		return (-1);
+	}
+	if ((unsigned)fd >= SOPEN_MAX || f->f_flags == 0) {
+		errno = EBADF;
+		return (-1);
+	}
+
+	/* operation not defined on raw devices */
+	if (f->f_flags & F_RAW) {
+		errno = EOPNOTSUPP;
+		return (-1);
+	}
+
+	errno = (f->f_ops->fchmod)(f, m);
+	return (0);
+}