From 54755eba5f04aa18b4c3dd6facb62aed74ff35dd Mon Sep 17 00:00:00 2001
From: Alan Cox <alan@linux.intel.com>
Date: Sun, 31 Dec 2017 23:01:28 +0000
Subject: [PATCH] utils: update remount to handle mtab etc

Add a -n option for boot time
---
 Applications/util/remount.c | 92 +++++++++++++++++++++++++++++++++----
 1 file changed, 84 insertions(+), 8 deletions(-)

diff --git a/Applications/util/remount.c b/Applications/util/remount.c
index bfaf4f88..eba55e5c 100644
--- a/Applications/util/remount.c
+++ b/Applications/util/remount.c
@@ -4,12 +4,42 @@
 #include <sys/mount.h>
 #include <mntent.h>
 
-static char *getdev(char *arg)
+static int quiet;
+
+/* Strip ro and rw from the entry and append the correct one */
+/* Will want extending when we do nosuid */
+static char *modify_opts(char *opts, int flags)
+{
+	static char optbuf[_MAX_MNTLEN];
+	char *op = optbuf;
+	char *p = strtok(opts, ",");
+	while(p) {
+		if (strcmp(p, "ro") != 0 && strcmp(p, "rw") != 0) {
+			if (op != optbuf)
+				*op++ = ',';
+			strcpy(op, p);
+			op += strlen(p);
+		}
+		p = strtok(NULL,",");
+	}
+	if (flags & MS_RDONLY) {
+		if (op != optbuf)
+			*op++ = ',';
+		strcpy(op, "ro");
+		op += 2;
+	}
+	if (op == optbuf)
+		return "defaults";
+	*op = 0;
+	return optbuf;
+}
+
+static char *getdev(char *arg, char *p)
 {
 	FILE *f;
 	struct mntent *mnt;
 
-	f = setmntent("/etc/mtab", "r");
+	f = setmntent(p, "r");
 	if (f) {
 		while (mnt = getmntent(f)) {
 			if ((strcmp(mnt->mnt_fsname, arg) == 0) || (strcmp(mnt->mnt_dir, arg) == 0)) {
@@ -22,21 +52,60 @@ static char *getdev(char *arg)
 	return NULL;
 }
 
-/* FIXME: needs to update mtab entry / support nosuid etc ? */
+static void rewrite_mtab(char *name, flags)
+{
+	FILE *inpf, *outf;
+	struct mntent *mnt;
+
+	if (quiet)
+		return;
+
+	inpf = setmntent("/etc/mtab", "r");
+	if (!inpf) {
+		perror("Can't open /etc/mtab");
+		exit(1);
+	}
+	outf = setmntent("/etc/mtab.new", "w");
+	if (!outf) {
+		perror("Can't create temporary file");
+		exit(1);
+	}
+	/* Correct the options for the remounted entry */
+	while (mnt = getmntent(inpf)) {
+		if (strcmp(name, mnt->mnt_fsname) == 0)
+			mnt->mnt_opts = modify_opts(mnt->mnt_opts, flags);
+		addmntent(outf, mnt);
+	}
+	endmntent(inpf);
+	endmntent(outf);
+	if (rename("/etc/mtab.new", "/etc/mtab") < 0) {
+		perror("Error installing /etc/mtab");
+		exit(1);
+	}
+}
 
 int main(int argc, char *argv[])
 {
 	char *dev;
 	unsigned int flags;
-	
+
+	if (argc == 4 && strcmp(argv[1], "-n") == 0) {
+		argc--;
+		argv++;
+		quiet = 1;
+	}
 	if (argc != 3) {
 		fprintf(stderr, "%s: remount device [ro][rw]\n", argv[0]);
 		return 1;
 	}
 
-	dev = getdev(argv[1]);
-	if (!dev) dev = argv[1];
-	
+	dev = getdev(argv[1], "/etc/fstab");
+	if (!dev)
+		dev = getdev(argv[1], "/etc/mtab");
+	if (!dev)
+		dev = argv[1];
+
+	/* TODO - nosuid once supported */
 	if (strcmp(argv[2], "ro") == 0)
 		flags = MS_RDONLY|MS_REMOUNT;
 	else if (strcmp(argv[2], "rw") == 0)
@@ -45,10 +114,17 @@ int main(int argc, char *argv[])
 		fprintf(stderr, "%s: ro or rw required.\n", argv[0]);
 		return 1;
 	}
+
+	/* Rewrite first in case we are updating /etc to ro */
+	if (flags & MS_RDONLY)
+		rewrite_mtab(dev, flags);
 	
 	if (remount(dev, flags)) {
-		perror("umount");
+		perror("remount");
 		return 1;
 	}
+	/* Otherwise rewrite after in case /etc was ro */
+	if (!(flags & MS_RDONLY))
+		rewrite_mtab(dev, flags);
 	return 0;
 }
-- 
2.34.1