fileio: accept FILE* in addition to path in parse_env_file()

Most our other parsing functions do this, let's do this here too,
internally we accept that anyway. Also, the closely related
load_env_file() and load_env_file_pairs() also do this, so let's be
systematic.

src/basic/fileio.c

@@ -677,6 +677,7 @@ static int parse_env_file_push(
 }
 
 int parse_env_file(
+                FILE *f,
                 const char *fname,
                 const char *newline, ...) {
 
@@ -687,7 +688,7 @@ int parse_env_file(
                 newline = NEWLINE;
 
         va_start(ap, newline);
-        r = parse_env_file_internal(NULL, fname, newline, parse_env_file_push, &ap, &n_pushed);
+        r = parse_env_file_internal(f, fname, newline, parse_env_file_push, &ap, &n_pushed);
         va_end(ap);
 
         return r < 0 ? r : n_pushed;

src/basic/fileio.h

@@ -45,7 +45,7 @@ int read_full_stream(FILE *f, char **contents, size_t *size);
 
 int verify_file(const char *fn, const char *blob, bool accept_extra_nl);
 
-int parse_env_file(const char *fname, const char *separator, ...) _sentinel_;
+int parse_env_file(FILE *f, const char *fname, const char *separator, ...) _sentinel_;
 int load_env_file(FILE *f, const char *fname, const char *separator, char ***l);
 int load_env_file_pairs(FILE *f, const char *fname, const char *separator, char ***l);
 

src/basic/util.c

@@ -264,7 +264,7 @@ int container_get_leader(const char *machine, pid_t *pid) {
                 return -EINVAL;
 
         p = strjoina("/run/systemd/machines/", machine);
-        r = parse_env_file(p, NEWLINE, "LEADER", &s, "CLASS", &class, NULL);
+        r = parse_env_file(NULL, p, NEWLINE, "LEADER", &s, "CLASS", &class, NULL);
         if (r == -ENOENT)
                 return -EHOSTDOWN;
         if (r < 0)