From c313f09bfbaba40cc7a85d11f10dbb70f68621cd Mon Sep 17 00:00:00 2001
From: "Christian S.J. Peron" <csjp@FreeBSD.org>
Date: Tue, 30 Aug 2005 16:45:32 +0000
Subject: [PATCH] When using files as backing stores for devices, and the user
 has requested the device be created read+write, check to see if the backing
 store is read only through the use of the access(2) system call. If this
 check fails returning EACCES, EPERM or EROFS then gracefully downgrade the
 access to read only. Also print a warning message to stderr, informing the
 user that the access mode they requested is not available.

This behavior used to be handled by md(4) but was changed in revision 1.154

Discussed with:	pjd, phk, Dario Freni <saturnero at freesbie dot org>
Reviewed by:	phk
---
 sbin/mdconfig/mdconfig.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/sbin/mdconfig/mdconfig.c b/sbin/mdconfig/mdconfig.c
index 02f128763c2..e3ca148d7fa 100644
--- a/sbin/mdconfig/mdconfig.c
+++ b/sbin/mdconfig/mdconfig.c
@@ -12,6 +12,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <errno.h>
 #include <fcntl.h>
 #include <unistd.h>
 #include <inttypes.h>
@@ -233,6 +234,16 @@ main(int argc, char **argv)
 	if (cmdline == 2 && mdio.md_type == MD_VNODE)
 		if (mdio.md_file[0] == '\0')
 			errx(1, "must specify -f for -t vnode");
+	if (mdio.md_type == MD_VNODE &&
+	    (mdio.md_options & MD_READONLY) == 0) {
+		if (access(mdio.md_file, W_OK) < 0 &&
+		    (errno == EACCES || errno == EPERM || errno == EROFS)) {
+			fprintf(stderr,
+			    "WARNING: opening backing store: %s readonly\n",
+			    mdio.md_file);
+			mdio.md_options |= MD_READONLY;
+		}
+	}
 	if (action == LIST) {
 		if (mdio.md_options & MD_AUTOUNIT)
 			list(fd);