fstabinfo/mountinfo: ensure /etc/fstab exists before calling setmntent

This is based on a patch by A. Wilcox <awilfox.gentoo@foxkit.us>.

X-Gentoo-Bug: 478226
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=478226

X-Gentoo-Bug: 478226
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=478226

src/rc/fstabinfo.c

@@ -178,6 +178,9 @@ int main(int argc, char **argv)
 	FILE *fp;
 #endif
 
+	/* fail if there is no /etc/fstab */
+	if (!exists("/etc/fstab"))
+		eerrorx("/etc/fstab does not exist");
 	/* Ensure that we are only quiet when explicitly told to be */
 	unsetenv("EINFO_QUIET");
 

src/rc/mountinfo.c

@@ -297,6 +297,9 @@ getmntfile(const char *file)
 	struct mntent *ent = NULL;
 	FILE *fp;
 
+	if (!exists("/etc/fstab"))
+		return NULL;
+
 	fp = setmntent("/etc/fstab", "r");
 	while ((ent = getmntent(fp)))
 		if (strcmp(file, ent->mnt_dir) == 0)