core/manager: split out creation of serialization fd out to a helper

There is a slight change in behaviour: the user manager for root will create a
temporary file in /run/systemd, not /tmp. I don't think this matters, but
simplifies implementation.

src/basic/fileio.c

@@ -1342,6 +1342,25 @@ int open_tmpfile_linkable(const char *target, int flags, char **ret_path) {
         return fd;
 }
 
+int open_serialization_fd(const char *ident) {
+        int fd = -1;
+
+        fd = memfd_create(ident, MFD_CLOEXEC);
+        if (fd < 0) {
+                const char *path;
+
+                path = getpid() == 1 ? "/run/systemd" : "/tmp";
+                fd = open_tmpfile_unlinkable(path, O_RDWR|O_CLOEXEC);
+                if (fd < 0)
+                        return fd;
+
+                log_debug("Serializing %s to %s.", ident, path);
+        } else
+                log_debug("Serializing %s to memfd.", ident);
+
+        return fd;
+}
+
 int link_tmpfile(int fd, const char *path, const char *target) {
 
         assert(fd >= 0);

src/basic/fileio.h

@@ -84,6 +84,7 @@ int fputs_with_space(FILE *f, const char *s, const char *separator, bool *space)
 
 int open_tmpfile_unlinkable(const char *directory, int flags);
 int open_tmpfile_linkable(const char *target, int flags, char **ret_path);
+int open_serialization_fd(const char *ident);
 
 int link_tmpfile(int fd, const char *path, const char *target);
 

src/core/manager.c

@@ -2437,22 +2437,14 @@ void manager_send_unit_plymouth(Manager *m, Unit *u) {
 }
 
 int manager_open_serialization(Manager *m, FILE **_f) {
-        int fd = -1;
+        int fd;
         FILE *f;
 
         assert(_f);
 
-        fd = memfd_create("systemd-serialization", MFD_CLOEXEC);
-        if (fd < 0) {
-                const char *path;
-
-                path = MANAGER_IS_SYSTEM(m) ? "/run/systemd" : "/tmp";
-                fd = open_tmpfile_unlinkable(path, O_RDWR|O_CLOEXEC);
-                if (fd < 0)
-                        return -errno;
-                log_debug("Serializing state to %s.", path);
-        } else
-                log_debug("Serializing state to memfd.");
+        fd = open_serialization_fd("systemd-state");
+        if (fd < 0)
+                return fd;
 
         f = fdopen(fd, "w+");
         if (!f) {
@@ -2461,7 +2453,6 @@ int manager_open_serialization(Manager *m, FILE **_f) {
         }
 
         *_f = f;
-
         return 0;
 }
 

src/test/test-fd-util.c

@@ -94,10 +94,20 @@ static void test_same_fd(void) {
         assert_se(same_fd(b, a) == 0);
 }
 
+static void test_open_serialization_fd(void) {
+        _cleanup_close_ int fd = -1;
+
+        fd = open_serialization_fd("test");
+        assert_se(fd >= 0);
+
+        write(fd, "test\n", 5);
+}
+
 int main(int argc, char *argv[]) {
         test_close_many();
         test_close_nointr();
         test_same_fd();
+        test_open_serialization_fd();
 
         return 0;
 }