+/* Check whether memory usage may have dropped below critical thresholds for
+ * waking up waiting threads. */
+void flushd_check_wakeup(BlueSkyFS *fs)
+{
+ int dirty = g_atomic_int_get(&fs->cache_dirty);
+ dirty += g_atomic_int_get(&fs->cache_log_dirty);
+
+ if (dirty <= bluesky_watermark_high_dirty)
+ g_cond_broadcast(fs->flushd_cond);
+}
+
+/* Try to flush dirty data to disk, either due to memory pressure or due to
+ * timeouts. */
+static void flushd_dirty(BlueSkyFS *fs)
+{
+ int64_t start_time = bluesky_get_current_time();
+ g_mutex_lock(fs->lock);
+
+ while (1) {
+ BlueSkyInode *inode;
+ if (fs->unlogged_list.prev == NULL)
+ break;
+ inode = fs->unlogged_list.prev->data;
+
+ if (bluesky_verbose) {
+ g_log("bluesky/flushd", G_LOG_LEVEL_DEBUG,
+ "Considering flushing inode %"PRIu64, inode->inum);
+ }
+
+ /* Stop processing dirty inodes if we both have enough memory available
+ * and the oldest inode is sufficiently new that it need not be flushed
+ * out. */
+ uint64_t elapsed = bluesky_get_current_time() - inode->change_time;
+ if (g_atomic_int_get(&fs->cache_dirty) < bluesky_watermark_low_dirty
+ && elapsed < WRITEBACK_DELAY)
+ break;
+ if (inode->change_time > start_time)
+ break;
+
+ bluesky_inode_ref(inode);
+
+ g_mutex_unlock(fs->lock);
+
+ g_mutex_lock(inode->lock);
+ flushd_dirty_inode(inode);
+ g_mutex_unlock(inode->lock);
+ bluesky_inode_unref(inode);
+
+ g_mutex_lock(fs->lock);
+ flushd_check_wakeup(fs);
+ }
+
+ g_cond_broadcast(fs->flushd_cond);
+
+ g_mutex_unlock(fs->lock);
+}
+
+/* Try to flush dirty data to the cloud. This will take a snapshot of the
+ * entire filesystem (though only point-in-time consistent for isolated inodes
+ * and not the filesystem as a whole) and ensure all data is written to the
+ * cloud. When the write completes, we will allow old journal segments (those
+ * that were fully written _before_ the snapshot process started) to be garbage
+ * collected. Newer journal segments can't be collected yet since they may
+ * still contain data which has not been written persistently to the cloud.
+ *
+ * Note that some of this code relies on the fact that only this thread of
+ * control (running flushd_cloud) is manipulating the inode map, and so
+ * concurrent updates to the inode map are prevented even without the
+ * filesystem lock held. Take great care if allowing multi-threaded access to
+ * the inode map... */
+static void flushd_cloud(BlueSkyFS *fs)
+{
+ g_mutex_lock(fs->lock);
+
+ /* TODO: Locking? Since we're reading a single variable this is probably
+ * atomic but a lock could be safer. */
+ BlueSkyCloudLog *marker = bluesky_log_get_commit_point(fs);
+ int journal_seq_start = fs->log->seq_num;
+
+ while (1) {
+ BlueSkyInode *inode;
+ if (fs->dirty_list.prev == NULL)
+ break;
+ inode = fs->dirty_list.prev->data;
+
+ if (bluesky_verbose) {
+ g_log("bluesky/flushd", G_LOG_LEVEL_DEBUG,
+ "Flushing inode %"PRIu64" to cloud", inode->inum);
+ }
+
+ bluesky_inode_ref(inode);
+
+ g_mutex_unlock(fs->lock);
+
+ g_mutex_lock(inode->lock);
+ g_assert(inode->change_cloud == inode->change_commit);
+ g_mutex_lock(fs->lock);
+ bluesky_list_unlink(&fs->dirty_list, inode->dirty_list);
+ inode->dirty_list = NULL;
+ g_mutex_unlock(fs->lock);
+
+ BlueSkyCloudLog *log = inode->committed_item;
+ inode->committed_item = NULL;
+ g_mutex_unlock(inode->lock);
+
+ if (log != NULL)
+ bluesky_cloudlog_serialize(log, fs);
+ bluesky_inode_unref(inode);
+ bluesky_cloudlog_unref(log);
+
+ g_mutex_lock(fs->lock);
+ }
+ g_mutex_unlock(fs->lock);
+
+ /* Write out any updated inode map entries, so that all inodes just written
+ * can be located, and then a final commit record. */
+ BlueSkyCloudLog *commit_record = bluesky_inode_map_serialize(fs);
+ if (commit_record != NULL) {
+ bluesky_cloudlog_serialize(commit_record, fs);
+ } else {
+ g_print("No need for a checkpoint record...\n");
+ }
+
+ bluesky_cloudlog_flush(fs);
+
+ /* Wait until all segments have been written to the cloud, so that it
+ * becomes safe to free up journal segments. */
+ while (fs->log_state->pending_segments != NULL) {
+ SerializedRecord *segment
+ = (SerializedRecord *)fs->log_state->pending_segments->data;
+ g_mutex_lock(segment->lock);
+ while (!segment->complete)
+ g_cond_wait(segment->cond, segment->lock);
+ g_mutex_unlock(segment->lock);
+
+ g_mutex_free(segment->lock);
+ g_cond_free(segment->cond);
+ g_free(segment);
+
+ fs->log_state->pending_segments
+ = g_list_delete_link(fs->log_state->pending_segments,
+ fs->log_state->pending_segments);
+ }
+
+ bluesky_log_write_commit_point(fs, marker);
+ bluesky_cloudlog_unref(commit_record);
+
+ g_print("All segments have been flushed, journal < %d is clean\n",
+ journal_seq_start);
+
+ fs->log->journal_watermark = journal_seq_start;
+
+ bluesky_inode_map_minimize(fs);
+}
+
+/* Drop cached data for a given inode, if it is clean. inode must be locked. */
+static void drop_caches(BlueSkyInode *inode)