libsysprof-profile: tail journald and append logs to capture

It can be handy to get system information from journald to correlate with
what is going on in applications. This simple journald tail GSource will
dispatch to our callback which can append the logs to the capture.

This uses a custom callback rather than the GSourceFunc because that seems
a bit annoying to use with recent GCC function equivalence checks.

src/libsysprof-profile/sysprof-journald-source.c

@@ -0,0 +1,107 @@
+/* sysprof-journald-source.c
+ *
+ * Copyright 2023 Christian Hergert <chergert@redhat.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#include "config.h"
+
+#include <systemd/sd-journal.h>
+
+#include "sysprof-journald-source.h"
+
+typedef struct _SysprofJournaldSource
+{
+  GSource                    parent_instance;
+  sd_journal                *journal;
+  SysprofJournaldSourceFunc  func;
+  gpointer                   func_data;
+  GDestroyNotify             func_data_destroy;
+} SysprofJournaldSource;
+
+static void
+sysprof_journald_source_finalize (GSource *source)
+{
+  SysprofJournaldSource *self = (SysprofJournaldSource *)source;
+
+  if (self->func_data_destroy)
+    self->func_data_destroy (self->func_data);
+
+  g_clear_pointer (&self->journal, sd_journal_close);
+}
+
+static gboolean
+sysprof_journald_source_dispatch (GSource     *source,
+                                  GSourceFunc  callback,
+                                  gpointer     user_data)
+{
+  SysprofJournaldSource *self = (SysprofJournaldSource *)source;
+
+  if (sd_journal_process (self->journal) == SD_JOURNAL_APPEND)
+    {
+      if (sd_journal_next (self->journal) > 0)
+        return self->func (self->func_data, self->journal);
+    }
+
+  return G_SOURCE_CONTINUE;
+}
+
+static GSourceFuncs sysprof_journald_source_funcs = {
+  .dispatch = sysprof_journald_source_dispatch,
+  .finalize = sysprof_journald_source_finalize,
+};
+
+GSource *
+sysprof_journald_source_new (SysprofJournaldSourceFunc func,
+                             gpointer                  func_data,
+                             GDestroyNotify            func_data_destroy)
+{
+  SysprofJournaldSource *self;
+  sd_journal *journal = NULL;
+  int fd;
+
+  if (sd_journal_open (&journal, 0) < 0)
+    return NULL;
+
+  if (sd_journal_seek_tail (journal) < 0)
+    goto failure;
+
+  if (sd_journal_previous (journal) < 0)
+    goto failure;
+
+  if (sd_journal_next (journal) < 0)
+    goto failure;
+
+  if (-1 == (fd = sd_journal_get_fd (journal)))
+    goto failure;
+
+  self = (SysprofJournaldSource *)g_source_new (&sysprof_journald_source_funcs,
+                                                sizeof (SysprofJournaldSource));
+  self->journal = journal;
+  self->func = func;
+  self->func_data = func_data;
+  self->func_data_destroy = func_data_destroy;
+
+  g_source_add_unix_fd ((GSource *)self, fd, sd_journal_get_events (journal));
+
+  return (GSource *)self;
+
+failure:
+  g_clear_pointer (&journal, sd_journal_close);
+
+  return NULL;
+}