Allow overriding /etc/fstab with $SYSTEMD_FSTAB

src/shared/fstab-util.c

@@ -19,7 +19,7 @@ int fstab_has_fstype(const char *fstype) {
         _cleanup_endmntent_ FILE *f = NULL;
         struct mntent *m;
 
-        f = setmntent("/etc/fstab", "re");
+        f = setmntent(fstab_path(), "re");
         if (!f)
                 return errno == ENOENT ? false : -errno;
 
@@ -39,7 +39,7 @@ int fstab_is_mount_point(const char *mount) {
         _cleanup_endmntent_ FILE *f = NULL;
         struct mntent *m;
 
-        f = setmntent("/etc/fstab", "re");
+        f = setmntent(fstab_path(), "re");
         if (!f)
                 return errno == ENOENT ? false : -errno;
 

src/shared/fstab-util.h

@@ -31,3 +31,7 @@ static inline bool fstab_test_yes_no_option(const char *opts, const char *yes_no
 }
 
 char *fstab_node_to_udev_node(const char *p);
+
+static inline const char* fstab_path(void) {
+        return secure_getenv("SYSTEMD_FSTAB") ?: "/etc/fstab";
+}