git@vger.kernel.org list mirror (unofficial, one of many)
 help / color / mirror / code / Atom feed
0a2d1c1162b9ee47ae2679b14c7f857f6aa7287c blob 25949 bytes (raw)

   1
   2
   3
   4
   5
   6
   7
   8
   9
  10
  11
  12
  13
  14
  15
  16
  17
  18
  19
  20
  21
  22
  23
  24
  25
  26
  27
  28
  29
  30
  31
  32
  33
  34
  35
  36
  37
  38
  39
  40
  41
  42
  43
  44
  45
  46
  47
  48
  49
  50
  51
  52
  53
  54
  55
  56
  57
  58
  59
  60
  61
  62
  63
  64
  65
  66
  67
  68
  69
  70
  71
  72
  73
  74
  75
  76
  77
  78
  79
  80
  81
  82
  83
  84
  85
  86
  87
  88
  89
  90
  91
  92
  93
  94
  95
  96
  97
  98
  99
 100
 101
 102
 103
 104
 105
 106
 107
 108
 109
 110
 111
 112
 113
 114
 115
 116
 117
 118
 119
 120
 121
 122
 123
 124
 125
 126
 127
 128
 129
 130
 131
 132
 133
 134
 135
 136
 137
 138
 139
 140
 141
 142
 143
 144
 145
 146
 147
 148
 149
 150
 151
 152
 153
 154
 155
 156
 157
 158
 159
 160
 161
 162
 163
 164
 165
 166
 167
 168
 169
 170
 171
 172
 173
 174
 175
 176
 177
 178
 179
 180
 181
 182
 183
 184
 185
 186
 187
 188
 189
 190
 191
 192
 193
 194
 195
 196
 197
 198
 199
 200
 201
 202
 203
 204
 205
 206
 207
 208
 209
 210
 211
 212
 213
 214
 215
 216
 217
 218
 219
 220
 221
 222
 223
 224
 225
 226
 227
 228
 229
 230
 231
 232
 233
 234
 235
 236
 237
 238
 239
 240
 241
 242
 243
 244
 245
 246
 247
 248
 249
 250
 251
 252
 253
 254
 255
 256
 257
 258
 259
 260
 261
 262
 263
 264
 265
 266
 267
 268
 269
 270
 271
 272
 273
 274
 275
 276
 277
 278
 279
 280
 281
 282
 283
 284
 285
 286
 287
 288
 289
 290
 291
 292
 293
 294
 295
 296
 297
 298
 299
 300
 301
 302
 303
 304
 305
 306
 307
 308
 309
 310
 311
 312
 313
 314
 315
 316
 317
 318
 319
 320
 321
 322
 323
 324
 325
 326
 327
 328
 329
 330
 331
 332
 333
 334
 335
 336
 337
 338
 339
 340
 341
 342
 343
 344
 345
 346
 347
 348
 349
 350
 351
 352
 353
 354
 355
 356
 357
 358
 359
 360
 361
 362
 363
 364
 365
 366
 367
 368
 369
 370
 371
 372
 373
 374
 375
 376
 377
 378
 379
 380
 381
 382
 383
 384
 385
 386
 387
 388
 389
 390
 391
 392
 393
 394
 395
 396
 397
 398
 399
 400
 401
 402
 403
 404
 405
 406
 407
 408
 409
 410
 411
 412
 413
 414
 415
 416
 417
 418
 419
 420
 421
 422
 423
 424
 425
 426
 427
 428
 429
 430
 431
 432
 433
 434
 435
 436
 437
 438
 439
 440
 441
 442
 443
 444
 445
 446
 447
 448
 449
 450
 451
 452
 453
 454
 455
 456
 457
 458
 459
 460
 461
 462
 463
 464
 465
 466
 467
 468
 469
 470
 471
 472
 473
 474
 475
 476
 477
 478
 479
 480
 481
 482
 483
 484
 485
 486
 487
 488
 489
 490
 491
 492
 493
 494
 495
 496
 497
 498
 499
 500
 501
 502
 503
 504
 505
 506
 507
 508
 509
 510
 511
 512
 513
 514
 515
 516
 517
 518
 519
 520
 521
 522
 523
 524
 525
 526
 527
 528
 529
 530
 531
 532
 533
 534
 535
 536
 537
 538
 539
 540
 541
 542
 543
 544
 545
 546
 547
 548
 549
 550
 551
 552
 553
 554
 555
 556
 557
 558
 559
 560
 561
 562
 563
 564
 565
 566
 567
 568
 569
 570
 571
 572
 573
 574
 575
 576
 577
 578
 579
 580
 581
 582
 583
 584
 585
 586
 587
 588
 589
 590
 591
 592
 593
 594
 595
 596
 597
 598
 599
 600
 601
 602
 603
 604
 605
 606
 607
 608
 609
 610
 611
 612
 613
 614
 615
 616
 617
 618
 619
 620
 621
 622
 623
 624
 625
 626
 627
 628
 629
 630
 631
 632
 633
 634
 635
 636
 637
 638
 639
 640
 641
 642
 643
 644
 645
 646
 647
 648
 649
 650
 651
 652
 653
 654
 655
 656
 657
 658
 659
 660
 661
 662
 663
 664
 665
 666
 667
 668
 669
 670
 671
 672
 673
 674
 675
 676
 677
 678
 679
 680
 681
 682
 683
 684
 685
 686
 687
 688
 689
 690
 691
 692
 693
 694
 695
 696
 697
 698
 699
 700
 701
 702
 703
 704
 705
 706
 707
 708
 709
 710
 711
 712
 713
 714
 715
 716
 717
 718
 719
 720
 721
 722
 723
 724
 725
 726
 727
 728
 729
 730
 731
 732
 733
 734
 735
 736
 737
 738
 739
 740
 741
 742
 743
 744
 745
 746
 747
 748
 749
 750
 751
 752
 753
 754
 755
 756
 757
 758
 759
 760
 761
 762
 763
 764
 765
 766
 767
 768
 769
 770
 771
 772
 773
 774
 775
 776
 777
 778
 779
 780
 781
 782
 783
 784
 785
 786
 787
 788
 789
 790
 791
 792
 793
 794
 795
 796
 797
 798
 799
 800
 801
 802
 803
 804
 805
 806
 807
 808
 809
 810
 811
 812
 813
 814
 815
 816
 817
 818
 819
 820
 821
 822
 823
 824
 825
 826
 827
 828
 829
 830
 831
 832
 833
 834
 835
 836
 837
 838
 839
 840
 841
 842
 843
 844
 845
 846
 847
 848
 849
 850
 851
 852
 853
 854
 855
 856
 857
 858
 859
 860
 861
 862
 863
 864
 865
 866
 867
 868
 869
 870
 871
 872
 873
 874
 875
 876
 877
 878
 879
 880
 881
 882
 883
 884
 885
 886
 887
 888
 889
 890
 891
 892
 893
 894
 895
 896
 897
 898
 899
 900
 901
 902
 903
 904
 905
 906
 907
 908
 909
 910
 911
 912
 913
 914
 915
 916
 917
 918
 919
 920
 921
 922
 923
 924
 925
 926
 927
 928
 929
 930
 931
 932
 933
 934
 935
 936
 937
 938
 939
 940
 941
 942
 943
 944
 945
 946
 947
 948
 949
 950
 951
 952
 953
 954
 955
 956
 957
 958
 959
 960
 961
 962
 963
 964
 965
 966
 967
 968
 969
 970
 971
 972
 973
 974
 975
 976
 977
 978
 979
 980
 981
 982
 983
 984
 985
 986
 987
 988
 989
 990
 991
 992
 993
 994
 995
 996
 997
 998
 999
1000
1001
1002
1003
 
#include "cache.h"
#include "simple-ipc.h"
#include "strbuf.h"
#include "pkt-line.h"
#include "thread-utils.h"
#include "unix-socket.h"
#include "unix-stream-server.h"

#ifdef NO_UNIX_SOCKETS
#error compat/simple-ipc/ipc-unix-socket.c requires Unix sockets
#endif

enum ipc_active_state ipc_get_active_state(const char *path)
{
	enum ipc_active_state state = IPC_STATE__OTHER_ERROR;
	struct ipc_client_connect_options options
		= IPC_CLIENT_CONNECT_OPTIONS_INIT;
	struct stat st;
	struct ipc_client_connection *connection_test = NULL;

	options.wait_if_busy = 0;
	options.wait_if_not_found = 0;

	if (lstat(path, &st) == -1) {
		switch (errno) {
		case ENOENT:
		case ENOTDIR:
			return IPC_STATE__NOT_LISTENING;
		default:
			return IPC_STATE__INVALID_PATH;
		}
	}

	/* also complain if a plain file is in the way */
	if ((st.st_mode & S_IFMT) != S_IFSOCK)
		return IPC_STATE__INVALID_PATH;

	/*
	 * Just because the filesystem has a S_IFSOCK type inode
	 * at `path`, doesn't mean it that there is a server listening.
	 * Ping it to be sure.
	 */
	state = ipc_client_try_connect(path, &options, &connection_test);
	ipc_client_close_connection(connection_test);

	return state;
}

/*
 * Retry frequency when trying to connect to a server.
 *
 * This value should be short enough that we don't seriously delay our
 * caller, but not fast enough that our spinning puts pressure on the
 * system.
 */
#define WAIT_STEP_MS (50)

/*
 * Try to connect to the server.  If the server is just starting up or
 * is very busy, we may not get a connection the first time.
 */
static enum ipc_active_state connect_to_server(
	const char *path,
	int timeout_ms,
	const struct ipc_client_connect_options *options,
	int *pfd)
{
	int k;

	*pfd = -1;

	for (k = 0; k < timeout_ms; k += WAIT_STEP_MS) {
		int fd = unix_stream_connect(path, options->uds_disallow_chdir);

		if (fd != -1) {
			*pfd = fd;
			return IPC_STATE__LISTENING;
		}

		if (errno == ENOENT) {
			if (!options->wait_if_not_found)
				return IPC_STATE__PATH_NOT_FOUND;

			goto sleep_and_try_again;
		}

		if (errno == ETIMEDOUT) {
			if (!options->wait_if_busy)
				return IPC_STATE__NOT_LISTENING;

			goto sleep_and_try_again;
		}

		if (errno == ECONNREFUSED) {
			if (!options->wait_if_busy)
				return IPC_STATE__NOT_LISTENING;

			goto sleep_and_try_again;
		}

		return IPC_STATE__OTHER_ERROR;

	sleep_and_try_again:
		sleep_millisec(WAIT_STEP_MS);
	}

	return IPC_STATE__NOT_LISTENING;
}

/*
 * The total amount of time that we are willing to wait when trying to
 * connect to a server.
 *
 * When the server is first started, it might take a little while for
 * it to become ready to service requests.  Likewise, the server may
 * be very (temporarily) busy and not respond to our connections.
 *
 * We should gracefully and silently handle those conditions and try
 * again for a reasonable time period.
 *
 * The value chosen here should be long enough for the server
 * to reliably heal from the above conditions.
 */
#define MY_CONNECTION_TIMEOUT_MS (1000)

enum ipc_active_state ipc_client_try_connect(
	const char *path,
	const struct ipc_client_connect_options *options,
	struct ipc_client_connection **p_connection)
{
	enum ipc_active_state state = IPC_STATE__OTHER_ERROR;
	int fd = -1;

	*p_connection = NULL;

	trace2_region_enter("ipc-client", "try-connect", NULL);
	trace2_data_string("ipc-client", NULL, "try-connect/path", path);

	state = connect_to_server(path, MY_CONNECTION_TIMEOUT_MS,
				  options, &fd);

	trace2_data_intmax("ipc-client", NULL, "try-connect/state",
			   (intmax_t)state);
	trace2_region_leave("ipc-client", "try-connect", NULL);

	if (state == IPC_STATE__LISTENING) {
		(*p_connection) = xcalloc(1, sizeof(struct ipc_client_connection));
		(*p_connection)->fd = fd;
	}

	return state;
}

void ipc_client_close_connection(struct ipc_client_connection *connection)
{
	if (!connection)
		return;

	if (connection->fd != -1)
		close(connection->fd);

	free(connection);
}

int ipc_client_send_command_to_connection(
	struct ipc_client_connection *connection,
	const char *message, size_t message_len,
	struct strbuf *answer)
{
	int ret = 0;

	strbuf_setlen(answer, 0);

	trace2_region_enter("ipc-client", "send-command", NULL);

	if (write_packetized_from_buf_no_flush(message, message_len,
					       connection->fd) < 0 ||
	    packet_flush_gently(connection->fd) < 0) {
		ret = error(_("could not send IPC command"));
		goto done;
	}

	if (read_packetized_to_strbuf(
		    connection->fd, answer,
		    PACKET_READ_GENTLE_ON_EOF | PACKET_READ_GENTLE_ON_READ_ERROR) < 0) {
		ret = error(_("could not read IPC response"));
		goto done;
	}

done:
	trace2_region_leave("ipc-client", "send-command", NULL);
	return ret;
}

int ipc_client_send_command(const char *path,
			    const struct ipc_client_connect_options *options,
			    const char *message, size_t message_len,
			    struct strbuf *answer)
{
	int ret = -1;
	enum ipc_active_state state;
	struct ipc_client_connection *connection = NULL;

	state = ipc_client_try_connect(path, options, &connection);

	if (state != IPC_STATE__LISTENING)
		return ret;

	ret = ipc_client_send_command_to_connection(connection,
						    message, message_len,
						    answer);

	ipc_client_close_connection(connection);

	return ret;
}

static int set_socket_blocking_flag(int fd, int make_nonblocking)
{
	int flags;

	flags = fcntl(fd, F_GETFL, NULL);

	if (flags < 0)
		return -1;

	if (make_nonblocking)
		flags |= O_NONBLOCK;
	else
		flags &= ~O_NONBLOCK;

	return fcntl(fd, F_SETFL, flags);
}

/*
 * Magic numbers used to annotate callback instance data.
 * These are used to help guard against accidentally passing the
 * wrong instance data across multiple levels of callbacks (which
 * is easy to do if there are `void*` arguments).
 */
enum magic {
	MAGIC_SERVER_REPLY_DATA,
	MAGIC_WORKER_THREAD_DATA,
	MAGIC_ACCEPT_THREAD_DATA,
	MAGIC_SERVER_DATA,
};

struct ipc_server_reply_data {
	enum magic magic;
	int fd;
	struct ipc_worker_thread_data *worker_thread_data;
};

struct ipc_worker_thread_data {
	enum magic magic;
	struct ipc_worker_thread_data *next_thread;
	struct ipc_server_data *server_data;
	pthread_t pthread_id;
};

struct ipc_accept_thread_data {
	enum magic magic;
	struct ipc_server_data *server_data;

	struct unix_ss_socket *server_socket;

	int fd_send_shutdown;
	int fd_wait_shutdown;
	pthread_t pthread_id;
};

/*
 * With unix-sockets, the conceptual "ipc-server" is implemented as a single
 * controller "accept-thread" thread and a pool of "worker-thread" threads.
 * The former does the usual `accept()` loop and dispatches connections
 * to an idle worker thread.  The worker threads wait in an idle loop for
 * a new connection, communicate with the client and relay data to/from
 * the `application_cb` and then wait for another connection from the
 * server thread.  This avoids the overhead of constantly creating and
 * destroying threads.
 */
struct ipc_server_data {
	enum magic magic;
	ipc_server_application_cb *application_cb;
	void *application_data;
	struct strbuf buf_path;

	struct ipc_accept_thread_data *accept_thread;
	struct ipc_worker_thread_data *worker_thread_list;

	pthread_mutex_t work_available_mutex;
	pthread_cond_t work_available_cond;

	/*
	 * Accepted but not yet processed client connections are kept
	 * in a circular buffer FIFO.  The queue is empty when the
	 * positions are equal.
	 */
	int *fifo_fds;
	int queue_size;
	int back_pos;
	int front_pos;

	int shutdown_requested;
	int is_stopped;
};

/*
 * Remove and return the oldest queued connection.
 *
 * Returns -1 if empty.
 */
static int fifo_dequeue(struct ipc_server_data *server_data)
{
	/* ASSERT holding mutex */

	int fd;

	if (server_data->back_pos == server_data->front_pos)
		return -1;

	fd = server_data->fifo_fds[server_data->front_pos];
	server_data->fifo_fds[server_data->front_pos] = -1;

	server_data->front_pos++;
	if (server_data->front_pos == server_data->queue_size)
		server_data->front_pos = 0;

	return fd;
}

/*
 * Push a new fd onto the back of the queue.
 *
 * Drop it and return -1 if queue is already full.
 */
static int fifo_enqueue(struct ipc_server_data *server_data, int fd)
{
	/* ASSERT holding mutex */

	int next_back_pos;

	next_back_pos = server_data->back_pos + 1;
	if (next_back_pos == server_data->queue_size)
		next_back_pos = 0;

	if (next_back_pos == server_data->front_pos) {
		/* Queue is full. Just drop it. */
		close(fd);
		return -1;
	}

	server_data->fifo_fds[server_data->back_pos] = fd;
	server_data->back_pos = next_back_pos;

	return fd;
}

/*
 * Wait for a connection to be queued to the FIFO and return it.
 *
 * Returns -1 if someone has already requested a shutdown.
 */
static int worker_thread__wait_for_connection(
	struct ipc_worker_thread_data *worker_thread_data)
{
	/* ASSERT NOT holding mutex */

	struct ipc_server_data *server_data = worker_thread_data->server_data;
	int fd = -1;

	pthread_mutex_lock(&server_data->work_available_mutex);
	for (;;) {
		if (server_data->shutdown_requested)
			break;

		fd = fifo_dequeue(server_data);
		if (fd >= 0)
			break;

		pthread_cond_wait(&server_data->work_available_cond,
				  &server_data->work_available_mutex);
	}
	pthread_mutex_unlock(&server_data->work_available_mutex);

	return fd;
}

/*
 * Forward declare our reply callback function so that any compiler
 * errors are reported when we actually define the function (in addition
 * to any errors reported when we try to pass this callback function as
 * a parameter in a function call).  The former are easier to understand.
 */
static ipc_server_reply_cb do_io_reply_callback;

/*
 * Relay application's response message to the client process.
 * (We do not flush at this point because we allow the caller
 * to chunk data to the client thru us.)
 */
static int do_io_reply_callback(struct ipc_server_reply_data *reply_data,
		       const char *response, size_t response_len)
{
	if (reply_data->magic != MAGIC_SERVER_REPLY_DATA)
		BUG("reply_cb called with wrong instance data");

	return write_packetized_from_buf_no_flush(response, response_len,
						  reply_data->fd);
}

/* A randomly chosen value. */
#define MY_WAIT_POLL_TIMEOUT_MS (10)

/*
 * If the client hangs up without sending any data on the wire, just
 * quietly close the socket and ignore this client.
 *
 * This worker thread is committed to reading the IPC request data
 * from the client at the other end of this fd.  Wait here for the
 * client to actually put something on the wire -- because if the
 * client just does a ping (connect and hangup without sending any
 * data), our use of the pkt-line read routines will spew an error
 * message.
 *
 * Return -1 if the client hung up.
 * Return 0 if data (possibly incomplete) is ready.
 */
static int worker_thread__wait_for_io_start(
	struct ipc_worker_thread_data *worker_thread_data,
	int fd)
{
	struct ipc_server_data *server_data = worker_thread_data->server_data;
	struct pollfd pollfd[1];
	int result;

	for (;;) {
		pollfd[0].fd = fd;
		pollfd[0].events = POLLIN;

		result = poll(pollfd, 1, MY_WAIT_POLL_TIMEOUT_MS);
		if (result < 0) {
			if (errno == EINTR)
				continue;
			goto cleanup;
		}

		if (result == 0) {
			/* a timeout */

			int in_shutdown;

			pthread_mutex_lock(&server_data->work_available_mutex);
			in_shutdown = server_data->shutdown_requested;
			pthread_mutex_unlock(&server_data->work_available_mutex);

			/*
			 * If a shutdown is already in progress and this
			 * client has not started talking yet, just drop it.
			 */
			if (in_shutdown)
				goto cleanup;
			continue;
		}

		if (pollfd[0].revents & POLLHUP)
			goto cleanup;

		if (pollfd[0].revents & POLLIN)
			return 0;

		goto cleanup;
	}

cleanup:
	close(fd);
	return -1;
}

/*
 * Receive the request/command from the client and pass it to the
 * registered request-callback.  The request-callback will compose
 * a response and call our reply-callback to send it to the client.
 */
static int worker_thread__do_io(
	struct ipc_worker_thread_data *worker_thread_data,
	int fd)
{
	/* ASSERT NOT holding lock */

	struct strbuf buf = STRBUF_INIT;
	struct ipc_server_reply_data reply_data;
	int ret = 0;

	reply_data.magic = MAGIC_SERVER_REPLY_DATA;
	reply_data.worker_thread_data = worker_thread_data;

	reply_data.fd = fd;

	ret = read_packetized_to_strbuf(
		reply_data.fd, &buf,
		PACKET_READ_GENTLE_ON_EOF | PACKET_READ_GENTLE_ON_READ_ERROR);
	if (ret >= 0) {
		ret = worker_thread_data->server_data->application_cb(
			worker_thread_data->server_data->application_data,
			buf.buf, buf.len, do_io_reply_callback, &reply_data);

		packet_flush_gently(reply_data.fd);
	}
	else {
		/*
		 * The client probably disconnected/shutdown before it
		 * could send a well-formed message.  Ignore it.
		 */
	}

	strbuf_release(&buf);
	close(reply_data.fd);

	return ret;
}

/*
 * Block SIGPIPE on the current thread (so that we get EPIPE from
 * write() rather than an actual signal).
 *
 * Note that using sigchain_push() and _pop() to control SIGPIPE
 * around our IO calls is not thread safe:
 * [] It uses a global stack of handler frames.
 * [] It uses ALLOC_GROW() to resize it.
 * [] Finally, according to the `signal(2)` man-page:
 *    "The effects of `signal()` in a multithreaded process are unspecified."
 */
static void thread_block_sigpipe(sigset_t *old_set)
{
	sigset_t new_set;

	sigemptyset(&new_set);
	sigaddset(&new_set, SIGPIPE);

	sigemptyset(old_set);
	pthread_sigmask(SIG_BLOCK, &new_set, old_set);
}

/*
 * Thread proc for an IPC worker thread.  It handles a series of
 * connections from clients.  It pulls the next fd from the queue
 * processes it, and then waits for the next client.
 *
 * Block SIGPIPE in this worker thread for the life of the thread.
 * This avoids stray (and sometimes delayed) SIGPIPE signals caused
 * by client errors and/or when we are under extremely heavy IO load.
 *
 * This means that the application callback will have SIGPIPE blocked.
 * The callback should not change it.
 */
static void *worker_thread_proc(void *_worker_thread_data)
{
	struct ipc_worker_thread_data *worker_thread_data = _worker_thread_data;
	struct ipc_server_data *server_data = worker_thread_data->server_data;
	sigset_t old_set;
	int fd, io;
	int ret;

	trace2_thread_start("ipc-worker");

	thread_block_sigpipe(&old_set);

	for (;;) {
		fd = worker_thread__wait_for_connection(worker_thread_data);
		if (fd == -1)
			break; /* in shutdown */

		io = worker_thread__wait_for_io_start(worker_thread_data, fd);
		if (io == -1)
			continue; /* client hung up without sending anything */

		ret = worker_thread__do_io(worker_thread_data, fd);

		if (ret == SIMPLE_IPC_QUIT) {
			trace2_data_string("ipc-worker", NULL, "queue_stop_async",
					   "application_quit");
			/*
			 * The application layer is telling the ipc-server
			 * layer to shutdown.
			 *
			 * We DO NOT have a response to send to the client.
			 *
			 * Queue an async stop (to stop the other threads) and
			 * allow this worker thread to exit now (no sense waiting
			 * for the thread-pool shutdown signal).
			 *
			 * Other non-idle worker threads are allowed to finish
			 * responding to their current clients.
			 */
			ipc_server_stop_async(server_data);
			break;
		}
	}

	trace2_thread_exit();
	return NULL;
}

/* A randomly chosen value. */
#define MY_ACCEPT_POLL_TIMEOUT_MS (60 * 1000)

/*
 * Accept a new client connection on our socket.  This uses non-blocking
 * IO so that we can also wait for shutdown requests on our socket-pair
 * without actually spinning on a fast timeout.
 */
static int accept_thread__wait_for_connection(
	struct ipc_accept_thread_data *accept_thread_data)
{
	struct pollfd pollfd[2];
	int result;

	for (;;) {
		pollfd[0].fd = accept_thread_data->fd_wait_shutdown;
		pollfd[0].events = POLLIN;

		pollfd[1].fd = accept_thread_data->server_socket->fd_socket;
		pollfd[1].events = POLLIN;

		result = poll(pollfd, 2, MY_ACCEPT_POLL_TIMEOUT_MS);
		if (result < 0) {
			if (errno == EINTR)
				continue;
			return result;
		}

		if (result == 0) {
			/* a timeout */

			/*
			 * If someone deletes or force-creates a new unix
			 * domain socket at our path, all future clients
			 * will be routed elsewhere and we silently starve.
			 * If that happens, just queue a shutdown.
			 */
			if (unix_ss_was_stolen(
				    accept_thread_data->server_socket)) {
				trace2_data_string("ipc-accept", NULL,
						   "queue_stop_async",
						   "socket_stolen");
				ipc_server_stop_async(
					accept_thread_data->server_data);
			}
			continue;
		}

		if (pollfd[0].revents & POLLIN) {
			/* shutdown message queued to socketpair */
			return -1;
		}

		if (pollfd[1].revents & POLLIN) {
			/* a connection is available on server_socket */

			int client_fd =
				accept(accept_thread_data->server_socket->fd_socket,
				       NULL, NULL);
			if (client_fd >= 0)
				return client_fd;

			/*
			 * An error here is unlikely -- it probably
			 * indicates that the connecting process has
			 * already dropped the connection.
			 */
			continue;
		}

		BUG("unandled poll result errno=%d r[0]=%d r[1]=%d",
		    errno, pollfd[0].revents, pollfd[1].revents);
	}
}

/*
 * Thread proc for the IPC server "accept thread".  This waits for
 * an incoming socket connection, appends it to the queue of available
 * connections, and notifies a worker thread to process it.
 *
 * Block SIGPIPE in this thread for the life of the thread.  This
 * avoids any stray SIGPIPE signals when closing pipe fds under
 * extremely heavy loads (such as when the fifo queue is full and we
 * drop incomming connections).
 */
static void *accept_thread_proc(void *_accept_thread_data)
{
	struct ipc_accept_thread_data *accept_thread_data = _accept_thread_data;
	struct ipc_server_data *server_data = accept_thread_data->server_data;
	sigset_t old_set;

	trace2_thread_start("ipc-accept");

	thread_block_sigpipe(&old_set);

	for (;;) {
		int client_fd = accept_thread__wait_for_connection(
			accept_thread_data);

		pthread_mutex_lock(&server_data->work_available_mutex);
		if (server_data->shutdown_requested) {
			pthread_mutex_unlock(&server_data->work_available_mutex);
			if (client_fd >= 0)
				close(client_fd);
			break;
		}

		if (client_fd < 0) {
			/* ignore transient accept() errors */
		}
		else {
			fifo_enqueue(server_data, client_fd);
			pthread_cond_broadcast(&server_data->work_available_cond);
		}
		pthread_mutex_unlock(&server_data->work_available_mutex);
	}

	trace2_thread_exit();
	return NULL;
}

/*
 * We can't predict the connection arrival rate relative to the worker
 * processing rate, therefore we allow the "accept-thread" to queue up
 * a generous number of connections, since we'd rather have the client
 * not unnecessarily timeout if we can avoid it.  (The assumption is
 * that this will be used for FSMonitor and a few second wait on a
 * connection is better than having the client timeout and do the full
 * computation itself.)
 *
 * The FIFO queue size is set to a multiple of the worker pool size.
 * This value chosen at random.
 */
#define FIFO_SCALE (100)

/*
 * The backlog value for `listen(2)`.  This doesn't need to huge,
 * rather just large enough for our "accept-thread" to wake up and
 * queue incoming connections onto the FIFO without the kernel
 * dropping any.
 *
 * This value chosen at random.
 */
#define LISTEN_BACKLOG (50)

static int create_listener_socket(
	const char *path,
	const struct ipc_server_opts *ipc_opts,
	struct unix_ss_socket **new_server_socket)
{
	struct unix_ss_socket *server_socket = NULL;
	struct unix_stream_listen_opts uslg_opts = UNIX_STREAM_LISTEN_OPTS_INIT;
	int ret;

	uslg_opts.listen_backlog_size = LISTEN_BACKLOG;
	uslg_opts.disallow_chdir = ipc_opts->uds_disallow_chdir;

	ret = unix_ss_create(path, &uslg_opts, -1, &server_socket);
	if (ret)
		return ret;

	if (set_socket_blocking_flag(server_socket->fd_socket, 1)) {
		int saved_errno = errno;
		unix_ss_free(server_socket);
		errno = saved_errno;
		return -1;
	}

	*new_server_socket = server_socket;

	trace2_data_string("ipc-server", NULL, "listen-with-lock", path);
	return 0;
}

static int setup_listener_socket(
	const char *path,
	const struct ipc_server_opts *ipc_opts,
	struct unix_ss_socket **new_server_socket)
{
	int ret, saved_errno;

	trace2_region_enter("ipc-server", "create-listener_socket", NULL);

	ret = create_listener_socket(path, ipc_opts, new_server_socket);

	saved_errno = errno;
	trace2_region_leave("ipc-server", "create-listener_socket", NULL);
	errno = saved_errno;

	return ret;
}

/*
 * Start IPC server in a pool of background threads.
 */
int ipc_server_run_async(struct ipc_server_data **returned_server_data,
			 const char *path, const struct ipc_server_opts *opts,
			 ipc_server_application_cb *application_cb,
			 void *application_data)
{
	struct unix_ss_socket *server_socket = NULL;
	struct ipc_server_data *server_data;
	int sv[2];
	int k;
	int ret;
	int nr_threads = opts->nr_threads;

	*returned_server_data = NULL;

	/*
	 * Create a socketpair and set sv[1] to non-blocking.  This
	 * will used to send a shutdown message to the accept-thread
	 * and allows the accept-thread to wait on EITHER a client
	 * connection or a shutdown request without spinning.
	 */
	if (socketpair(AF_UNIX, SOCK_STREAM, 0, sv) < 0)
		return -1;

	if (set_socket_blocking_flag(sv[1], 1)) {
		int saved_errno = errno;
		close(sv[0]);
		close(sv[1]);
		errno = saved_errno;
		return -1;
	}

	ret = setup_listener_socket(path, opts, &server_socket);
	if (ret) {
		int saved_errno = errno;
		close(sv[0]);
		close(sv[1]);
		errno = saved_errno;
		return ret;
	}

	server_data = xcalloc(1, sizeof(*server_data));
	server_data->magic = MAGIC_SERVER_DATA;
	server_data->application_cb = application_cb;
	server_data->application_data = application_data;
	strbuf_init(&server_data->buf_path, 0);
	strbuf_addstr(&server_data->buf_path, path);

	if (nr_threads < 1)
		nr_threads = 1;

	pthread_mutex_init(&server_data->work_available_mutex, NULL);
	pthread_cond_init(&server_data->work_available_cond, NULL);

	server_data->queue_size = nr_threads * FIFO_SCALE;
	CALLOC_ARRAY(server_data->fifo_fds, server_data->queue_size);

	server_data->accept_thread =
		xcalloc(1, sizeof(*server_data->accept_thread));
	server_data->accept_thread->magic = MAGIC_ACCEPT_THREAD_DATA;
	server_data->accept_thread->server_data = server_data;
	server_data->accept_thread->server_socket = server_socket;
	server_data->accept_thread->fd_send_shutdown = sv[0];
	server_data->accept_thread->fd_wait_shutdown = sv[1];

	if (pthread_create(&server_data->accept_thread->pthread_id, NULL,
			   accept_thread_proc, server_data->accept_thread))
		die_errno(_("could not start accept_thread '%s'"), path);

	for (k = 0; k < nr_threads; k++) {
		struct ipc_worker_thread_data *wtd;

		wtd = xcalloc(1, sizeof(*wtd));
		wtd->magic = MAGIC_WORKER_THREAD_DATA;
		wtd->server_data = server_data;

		if (pthread_create(&wtd->pthread_id, NULL, worker_thread_proc,
				   wtd)) {
			if (k == 0)
				die(_("could not start worker[0] for '%s'"),
				    path);
			/*
			 * Limp along with the thread pool that we have.
			 */
			break;
		}

		wtd->next_thread = server_data->worker_thread_list;
		server_data->worker_thread_list = wtd;
	}

	*returned_server_data = server_data;
	return 0;
}

/*
 * Gently tell the IPC server treads to shutdown.
 * Can be run on any thread.
 */
int ipc_server_stop_async(struct ipc_server_data *server_data)
{
	/* ASSERT NOT holding mutex */

	int fd;

	if (!server_data)
		return 0;

	trace2_region_enter("ipc-server", "server-stop-async", NULL);

	pthread_mutex_lock(&server_data->work_available_mutex);

	server_data->shutdown_requested = 1;

	/*
	 * Write a byte to the shutdown socket pair to wake up the
	 * accept-thread.
	 */
	if (write(server_data->accept_thread->fd_send_shutdown, "Q", 1) < 0)
		error_errno("could not write to fd_send_shutdown");

	/*
	 * Drain the queue of existing connections.
	 */
	while ((fd = fifo_dequeue(server_data)) != -1)
		close(fd);

	/*
	 * Gently tell worker threads to stop processing new connections
	 * and exit.  (This does not abort in-process conversations.)
	 */
	pthread_cond_broadcast(&server_data->work_available_cond);

	pthread_mutex_unlock(&server_data->work_available_mutex);

	trace2_region_leave("ipc-server", "server-stop-async", NULL);

	return 0;
}

/*
 * Wait for all IPC server threads to stop.
 */
int ipc_server_await(struct ipc_server_data *server_data)
{
	pthread_join(server_data->accept_thread->pthread_id, NULL);

	if (!server_data->shutdown_requested)
		BUG("ipc-server: accept-thread stopped for '%s'",
		    server_data->buf_path.buf);

	while (server_data->worker_thread_list) {
		struct ipc_worker_thread_data *wtd =
			server_data->worker_thread_list;

		pthread_join(wtd->pthread_id, NULL);

		server_data->worker_thread_list = wtd->next_thread;
		free(wtd);
	}

	server_data->is_stopped = 1;

	return 0;
}

void ipc_server_free(struct ipc_server_data *server_data)
{
	struct ipc_accept_thread_data * accept_thread_data;

	if (!server_data)
		return;

	if (!server_data->is_stopped)
		BUG("cannot free ipc-server while running for '%s'",
		    server_data->buf_path.buf);

	accept_thread_data = server_data->accept_thread;
	if (accept_thread_data) {
		unix_ss_free(accept_thread_data->server_socket);

		if (accept_thread_data->fd_send_shutdown != -1)
			close(accept_thread_data->fd_send_shutdown);
		if (accept_thread_data->fd_wait_shutdown != -1)
			close(accept_thread_data->fd_wait_shutdown);

		free(server_data->accept_thread);
	}

	while (server_data->worker_thread_list) {
		struct ipc_worker_thread_data *wtd =
			server_data->worker_thread_list;

		server_data->worker_thread_list = wtd->next_thread;
		free(wtd);
	}

	pthread_cond_destroy(&server_data->work_available_cond);
	pthread_mutex_destroy(&server_data->work_available_mutex);

	strbuf_release(&server_data->buf_path);

	free(server_data->fifo_fds);
	free(server_data);
}
debug log:

solving 0a2d1c1162b9 ...
found 0a2d1c1162b9 in https://public-inbox.org/git/763fa1ee7bb61d236cb0e7e2f01a3a03af87ac2d.1621691828.git.gitgitgadget@gmail.com/
found 38689b278df3 in git.git.git
preparing index
index prepared:
100644 38689b278df30e1366afb378a5cd9f1c7062da7f	compat/simple-ipc/ipc-unix-socket.c

applying [1/1] https://public-inbox.org/git/763fa1ee7bb61d236cb0e7e2f01a3a03af87ac2d.1621691828.git.gitgitgadget@gmail.com/
diff --git a/compat/simple-ipc/ipc-unix-socket.c b/compat/simple-ipc/ipc-unix-socket.c
index 38689b278df3..0a2d1c1162b9 100644

Checking patch compat/simple-ipc/ipc-unix-socket.c...
Applied patch compat/simple-ipc/ipc-unix-socket.c cleanly.

index at:
100644 0a2d1c1162b9ee47ae2679b14c7f857f6aa7287c	compat/simple-ipc/ipc-unix-socket.c

Code repositories for project(s) associated with this inbox:

	https://80x24.org/mirrors/git.git

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).