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

[Jeff Hostetler <git@jeffhostetler.com>]

On 3/22/22 2:30 PM, Ævar Arnfjörð Bjarmason wrote:
> 
> On Tue, Mar 22 2022, Jeff Hostetler via GitGitGadget wrote:
> 
>> 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;
> 
> Just noticed while skimming, isn't initializing do_trivial here (didn't
> exhaustively check the others) getting in the way of uninitialized
> analysis the compiler will do...
> 
>> +
>> +	/*
>> +	 * 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>"
>> +			 */
>> +		}
>> +	}
> 
> Since we'll set it here in all branches except the "else" branch,
> i.e. if you move this to "we have a v2 valid" we'll catch future bugs if
> we ever have it uninitialized still,

I suppose we could do it that way.  We'd want to do the same
for "do_flush" in that case.  I could go either way on this
change.


> 
>> +
>> +	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) {
> 
> I.e. this would start warning.
> 
>> +		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;
> 
> Nit: instead of strbuf_release() here, just a 'goto cleanup' and ...

Yeah, we could do that.  That would also do an unnecesssary release
of "payload", but that's not that bad (or I could order them at the
bottom).

I'm not sure either of these changes are enough for a re-roll,
but I'll include them if I do.

Thanks
Jeff

> 
>> +	}
>> +
>> +	/*
>> +	 * 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);
>> +
> 
> add a "cleanup" label here?
> 
>> +	strbuf_release(&response_token);
>> +	strbuf_release(&requested_token_id);
>> +	strbuf_release(&payload);
>> +
>> +	return 0;
>> +}
>> +
>>   static ipc_server_application_cb handle_client;