journald: support reloading configuration at runtime

src/libsystemd/sd-journal/journal-file.c

@@ -4082,6 +4082,54 @@ static void journal_default_metrics(JournalMetrics *m, int fd, bool compact) {
                   m->n_max_files);
 }
 
+static uint64_t get_compress_threshold_bytes(uint64_t compress_threshold_bytes) {
+        return compress_threshold_bytes == UINT64_MAX ?
+                DEFAULT_COMPRESS_THRESHOLD :
+                MAX(MIN_COMPRESS_THRESHOLD, compress_threshold_bytes);
+}
+
+static int set_metrics(JournalFile *f, JournalMetrics *metrics, JournalFile *template) {
+        assert(f);
+        int r;
+
+        if (!journal_file_writable(f))
+                return 0;
+
+        if (metrics) {
+                journal_default_metrics(metrics, f->fd, JOURNAL_HEADER_COMPACT(f->header));
+                f->metrics = *metrics;
+        } else if (template)
+                f->metrics = template->metrics;
+
+        r = journal_file_refresh_header(f);
+        if (r < 0)
+                return log_error_errno(r, "Failed to refresh journal file header. Error to be handled by caller.");
+
+        return 0;
+}
+
+int journal_file_reload(
+                JournalFile *f,
+                JournalFileFlags file_flags,
+                uint64_t compress_threshold_bytes,
+                JournalMetrics *metrics) {
+
+        assert(f);
+        assert((file_flags & ~_JOURNAL_FILE_FLAGS_ALL) == 0);
+        assert(metrics);
+
+        int r;
+
+        f->compress_threshold_bytes = get_compress_threshold_bytes(compress_threshold_bytes);
+
+        r = set_metrics(f, metrics, /* template */ NULL);
+        if (r < 0)
+                /* Journal file header failed to be rotated. The changes may not have taken effect in this case. */
+                return r;
+
+        return 0;
+}
+
 int journal_file_open(
                 int fd,
                 const char *fname,
@@ -4121,9 +4169,7 @@ int journal_file_open(
                 .fd = fd,
                 .mode = mode,
                 .open_flags = open_flags,
-                .compress_threshold_bytes = compress_threshold_bytes == UINT64_MAX ?
-                                            DEFAULT_COMPRESS_THRESHOLD :
-                                            MAX(MIN_COMPRESS_THRESHOLD, compress_threshold_bytes),
+                .compress_threshold_bytes = get_compress_threshold_bytes(compress_threshold_bytes),
                 .strict_order = FLAGS_SET(file_flags, JOURNAL_STRICT_ORDER),
                 .newest_boot_id_prioq_idx = PRIOQ_IDX_NULL,
                 .last_direction = _DIRECTION_INVALID,
@@ -4232,17 +4278,9 @@ int journal_file_open(
         }
 #endif
 
-        if (journal_file_writable(f)) {
-                if (metrics) {
-                        journal_default_metrics(metrics, f->fd, JOURNAL_HEADER_COMPACT(f->header));
-                        f->metrics = *metrics;
-                } else if (template)
-                        f->metrics = template->metrics;
-
-                r = journal_file_refresh_header(f);
-                if (r < 0)
-                        goto fail;
-        }
+        r = set_metrics(f, metrics, template);
+        if (r < 0)
+                goto fail;
 
 #if HAVE_GCRYPT
         r = journal_file_hmac_setup(f);

src/libsystemd/sd-journal/journal-file.h

@@ -149,6 +149,12 @@ int journal_file_open(
                 JournalFile *template,
                 JournalFile **ret);
 
+int journal_file_reload(
+        JournalFile *f,
+        JournalFileFlags file_flags,
+        uint64_t compress_threshold_bytes,
+        JournalMetrics *metrics);
+
 int journal_file_set_offline_thread_join(JournalFile *f);
 JournalFile* journal_file_close(JournalFile *j);
 int journal_file_fstat(JournalFile *f);