Re: [PATCH v7 18/29] fsmonitor--daemon: implement handle_client callback

> From: Jeff Hostetler <jeffhost@microsoft.com>
> [...]
> +static int do_handle_client(struct fsmonitor_daemon_state *state,
> +			    const char *command,
> +			    ipc_server_reply_cb *reply,
> +			    struct ipc_server_reply_data *reply_data)
> +{
> +	struct fsmonitor_token_data *token_data = NULL;
> +	struct strbuf response_token = STRBUF_INIT;
> +	struct strbuf requested_token_id = STRBUF_INIT;
> +	struct strbuf payload = STRBUF_INIT;
> +	uint64_t requested_oldest_seq_nr = 0;
> +	uint64_t total_response_len = 0;
> +	const char *p;
> +	const struct fsmonitor_batch *batch_head;
> +	const struct fsmonitor_batch *batch;
> +	intmax_t count = 0, duplicates = 0;
> +	kh_str_t *shown;
> +	int hash_ret;
> +	int do_trivial = 0;
> +	int do_flush = 0;

> +
> +	/*
> +	 * We expect `command` to be of the form:
> +	 *
> +	 * <command> := quit NUL
> +	 *            | flush NUL
> +	 *            | <V1-time-since-epoch-ns> NUL
> +	 *            | <V2-opaque-fsmonitor-token> NUL
> +	 */
> +
> +	if (!strcmp(command, "quit")) {
> +		/*
> +		 * A client has requested over the socket/pipe that the
> +		 * daemon shutdown.
> +		 *
> +		 * Tell the IPC thread pool to shutdown (which completes
> +		 * the await in the main thread (which can stop the
> +		 * fsmonitor listener thread)).
> +		 *
> +		 * There is no reply to the client.
> +		 */
> +		return SIMPLE_IPC_QUIT;
> +
> +	} else if (!strcmp(command, "flush")) {
> +		/*
> +		 * Flush all of our cached data and generate a new token
> +		 * just like if we lost sync with the filesystem.
> +		 *
> +		 * Then send a trivial response using the new token.
> +		 */
> +		do_flush = 1;
> +		do_trivial = 1;
> +
> +	} else if (!skip_prefix(command, "builtin:", &p)) {
> +		/* assume V1 timestamp or garbage */
> +
> +		char *p_end;
> +
> +		strtoumax(command, &p_end, 10);
> +		trace_printf_key(&trace_fsmonitor,
> +				 ((*p_end) ?
> +				  "fsmonitor: invalid command line '%s'" :
> +				  "fsmonitor: unsupported V1 protocol '%s'"),
> +				 command);
> +		do_trivial = 1;
> +
> +	} else {
> +		/* We have "builtin:*" */
> +		if (fsmonitor_parse_client_token(command, &requested_token_id,
> +						 &requested_oldest_seq_nr)) {
> +			trace_printf_key(&trace_fsmonitor,
> +					 "fsmonitor: invalid V2 protocol token '%s'",
> +					 command);
> +			do_trivial = 1;
> +
> +		} else {
> +			/*
> +			 * We have a V2 valid token:
> +			 *     "builtin:<token_id>:<seq_nr>"
> +			 */
> +		}
> +	}

> +
> +	pthread_mutex_lock(&state->main_lock);
> +
> +	if (!state->current_token_data)
> +		BUG("fsmonitor state does not have a current token");
> +
> +	if (do_flush)
> +		with_lock__do_force_resync(state);
> +
> +	/*
> +	 * We mark the current head of the batch list as "pinned" so
> +	 * that the listener thread will treat this item as read-only
> +	 * (and prevent any more paths from being added to it) from
> +	 * now on.
> +	 */
> +	token_data = state->current_token_data;
> +	batch_head = token_data->batch_head;
> +	((struct fsmonitor_batch *)batch_head)->pinned_time = time(NULL);
> +
> +	/*
> +	 * FSMonitor Protocol V2 requires that we send a response header
> +	 * with a "new current token" and then all of the paths that changed
> +	 * since the "requested token".  We send the seq_nr of the just-pinned
> +	 * head batch so that future requests from a client will be relative
> +	 * to it.
> +	 */
> +	with_lock__format_response_token(&response_token,
> +					 &token_data->token_id, batch_head);
> +
> +	reply(reply_data, response_token.buf, response_token.len + 1);
> +	total_response_len += response_token.len + 1;
> +
> +	trace2_data_string("fsmonitor", the_repository, "response/token",
> +			   response_token.buf);
> +	trace_printf_key(&trace_fsmonitor, "response token: %s",
> +			 response_token.buf);
> +
> +	if (!do_trivial) {

> +		if (strcmp(requested_token_id.buf, token_data->token_id.buf)) {
> +			/*
> +			 * The client last spoke to a different daemon
> +			 * instance -OR- the daemon had to resync with
> +			 * the filesystem (and lost events), so reject.
> +			 */
> +			trace2_data_string("fsmonitor", the_repository,
> +					   "response/token", "different");
> +			do_trivial = 1;
> +
> +		} else if (requested_oldest_seq_nr <
> +			   token_data->batch_tail->batch_seq_nr) {
> +			/*
> +			 * The client wants older events than we have for
> +			 * this token_id.  This means that the end of our
> +			 * batch list was truncated and we cannot give the
> +			 * client a complete snapshot relative to their
> +			 * request.
> +			 */
> +			trace_printf_key(&trace_fsmonitor,
> +					 "client requested truncated data");
> +			do_trivial = 1;
> +		}
> +	}
> +
> +	if (do_trivial) {
> +		pthread_mutex_unlock(&state->main_lock);
> +
> +		reply(reply_data, "/", 2);
> +
> +		trace2_data_intmax("fsmonitor", the_repository,
> +				   "response/trivial", 1);
> +
> +		strbuf_release(&response_token);
> +		strbuf_release(&requested_token_id);
> +		return 0;

> +	}
> +
> +	/*
> +	 * We're going to hold onto a pointer to the current
> +	 * token-data while we walk the list of batches of files.
> +	 * During this time, we will NOT be under the lock.
> +	 * So we ref-count it.
> +	 *
> +	 * This allows the listener thread to continue prepending
> +	 * new batches of items to the token-data (which we'll ignore).
> +	 *
> +	 * AND it allows the listener thread to do a token-reset
> +	 * (and install a new `current_token_data`).
> +	 */
> +	token_data->client_ref_count++;
> +
> +	pthread_mutex_unlock(&state->main_lock);
> +
> +	/*
> +	 * The client request is relative to the token that they sent,
> +	 * so walk the batch list backwards from the current head back
> +	 * to the batch (sequence number) they named.
> +	 *
> +	 * We use khash to de-dup the list of pathnames.
> +	 *
> +	 * NEEDSWORK: each batch contains a list of interned strings,
> +	 * so we only need to do pointer comparisons here to build the
> +	 * hash table.  Currently, we're still comparing the string
> +	 * values.
> +	 */
> +	shown = kh_init_str();
> +	for (batch = batch_head;
> +	     batch && batch->batch_seq_nr > requested_oldest_seq_nr;
> +	     batch = batch->next) {
> +		size_t k;
> +
> +		for (k = 0; k < batch->nr; k++) {
> +			const char *s = batch->interned_paths[k];
> +			size_t s_len;
> +
> +			if (kh_get_str(shown, s) != kh_end(shown))
> +				duplicates++;
> +			else {
> +				kh_put_str(shown, s, &hash_ret);
> +
> +				trace_printf_key(&trace_fsmonitor,
> +						 "send[%"PRIuMAX"]: %s",
> +						 count, s);
> +
> +				/* Each path gets written with a trailing NUL */
> +				s_len = strlen(s) + 1;
> +
> +				if (payload.len + s_len >=
> +				    LARGE_PACKET_DATA_MAX) {
> +					reply(reply_data, payload.buf,
> +					      payload.len);
> +					total_response_len += payload.len;
> +					strbuf_reset(&payload);
> +				}
> +
> +				strbuf_add(&payload, s, s_len);
> +				count++;
> +			}
> +		}
> +	}
> +
> +	if (payload.len) {
> +		reply(reply_data, payload.buf, payload.len);
> +		total_response_len += payload.len;
> +	}
> +
> +	kh_release_str(shown);
> +
> +	pthread_mutex_lock(&state->main_lock);
> +
> +	if (token_data->client_ref_count > 0)
> +		token_data->client_ref_count--;
> +
> +	if (token_data->client_ref_count == 0) {
> +		if (token_data != state->current_token_data) {
> +			/*
> +			 * The listener thread did a token-reset while we were
> +			 * walking the batch list.  Therefore, this token is
> +			 * stale and can be discarded completely.  If we are
> +			 * the last reader thread using this token, we own
> +			 * that work.
> +			 */
> +			fsmonitor_free_token_data(token_data);
> +		}
> +	}
> +
> +	pthread_mutex_unlock(&state->main_lock);
> +
> +	trace2_data_intmax("fsmonitor", the_repository, "response/length", total_response_len);
> +	trace2_data_intmax("fsmonitor", the_repository, "response/count/files", count);
> +	trace2_data_intmax("fsmonitor", the_repository, "response/count/duplicates", duplicates);
> +

> +	strbuf_release(&response_token);
> +	strbuf_release(&requested_token_id);
> +	strbuf_release(&payload);
> +
> +	return 0;
> +}
> +
>  static ipc_server_application_cb handle_client;