lib/socket-util.c

   1 /*
   2  * Copyright (c) 2008, 2009, 2010, 2011 Nicira Networks.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 #include <config.h>
  18 #include "socket-util.h"
  19 #include <arpa/inet.h>
  20 #include <errno.h>
  21 #include <fcntl.h>
  22 #include <net/if.h>
  23 #include <netdb.h>
  24 #include <poll.h>
  25 #include <stddef.h>
  26 #include <stdio.h>
  27 #include <stdlib.h>
  28 #include <string.h>
  29 #include <sys/resource.h>
  30 #include <sys/socket.h>
  31 #include <sys/stat.h>
  32 #include <sys/un.h>
  33 #include <unistd.h>
  34 #include "dynamic-string.h"
  35 #include "fatal-signal.h"
  36 #include "packets.h"
  37 #include "util.h"
  38 #include "vlog.h"
  39 #if AF_PACKET && __linux__
  40 #include <linux/if_packet.h>
  41 #endif
  42 #ifdef HAVE_NETLINK
  43 #include "netlink-protocol.h"
  44 #include "netlink-socket.h"
  45 #endif
  46
  47 VLOG_DEFINE_THIS_MODULE(socket_util);
  48
  49 /* #ifdefs make it a pain to maintain code: you have to try to build both ways.
  50  * Thus, this file compiles all of the code regardless of the target, by
  51  * writing "if (LINUX)" instead of "#ifdef __linux__". */
  52 #ifdef __linux__
  53 #define LINUX 1
  54 #else
  55 #define LINUX 0
  56 #endif
  57
  58 #ifndef O_DIRECTORY
  59 #define O_DIRECTORY 0
  60 #endif
  61
  62 /* Sets 'fd' to non-blocking mode.  Returns 0 if successful, otherwise a
  63  * positive errno value. */
  64 int
  65 set_nonblocking(int fd)
  66 {
  67     int flags = fcntl(fd, F_GETFL, 0);
  68     if (flags != -1) {
  69         if (fcntl(fd, F_SETFL, flags | O_NONBLOCK) != -1) {
  70             return 0;
  71         } else {
  72             VLOG_ERR("fcntl(F_SETFL) failed: %s", strerror(errno));
  73             return errno;
  74         }
  75     } else {
  76         VLOG_ERR("fcntl(F_GETFL) failed: %s", strerror(errno));
  77         return errno;
  78     }
  79 }
  80
  81 static bool
  82 rlim_is_finite(rlim_t limit)
  83 {
  84     if (limit == RLIM_INFINITY) {
  85         return false;
  86     }
  87
  88 #ifdef RLIM_SAVED_CUR           /* FreeBSD 8.0 lacks RLIM_SAVED_CUR. */
  89     if (limit == RLIM_SAVED_CUR) {
  90         return false;
  91     }
  92 #endif
  93
  94 #ifdef RLIM_SAVED_MAX           /* FreeBSD 8.0 lacks RLIM_SAVED_MAX. */
  95     if (limit == RLIM_SAVED_MAX) {
  96         return false;
  97     }
  98 #endif
  99
 100     return true;
 101 }
 102
 103 /* Returns the maximum valid FD value, plus 1. */
 104 int
 105 get_max_fds(void)
 106 {
 107     static int max_fds = -1;
 108     if (max_fds < 0) {
 109         struct rlimit r;
 110         if (!getrlimit(RLIMIT_NOFILE, &r) && rlim_is_finite(r.rlim_cur)) {
 111             max_fds = r.rlim_cur;
 112         } else {
 113             VLOG_WARN("failed to obtain fd limit, defaulting to 1024");
 114             max_fds = 1024;
 115         }
 116     }
 117     return max_fds;
 118 }
 119
 120 /* Translates 'host_name', which must be a string representation of an IP
 121  * address, into a numeric IP address in '*addr'.  Returns 0 if successful,
 122  * otherwise a positive errno value. */
 123 int
 124 lookup_ip(const char *host_name, struct in_addr *addr)
 125 {
 126     if (!inet_aton(host_name, addr)) {
 127         static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
 128         VLOG_ERR_RL(&rl, "\"%s\" is not a valid IP address", host_name);
 129         return ENOENT;
 130     }
 131     return 0;
 132 }
 133
 134 /* Translates 'host_name', which must be a string representation of an IPv6
 135  * address, into a numeric IPv6 address in '*addr'.  Returns 0 if successful,
 136  * otherwise a positive errno value. */
 137 int
 138 lookup_ipv6(const char *host_name, struct in6_addr *addr)
 139 {
 140     if (inet_pton(AF_INET6, host_name, addr) != 1) {
 141         static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 5);
 142         VLOG_ERR_RL(&rl, "\"%s\" is not a valid IPv6 address", host_name);
 143         return ENOENT;
 144     }
 145     return 0;
 146 }
 147
 148 /* Returns the error condition associated with socket 'fd' and resets the
 149  * socket's error status. */
 150 int
 151 get_socket_error(int fd)
 152 {
 153     int error;
 154     socklen_t len = sizeof(error);
 155     if (getsockopt(fd, SOL_SOCKET, SO_ERROR, &error, &len) < 0) {
 156         static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(5, 10);
 157         error = errno;
 158         VLOG_ERR_RL(&rl, "getsockopt(SO_ERROR): %s", strerror(error));
 159     }
 160     return error;
 161 }
 162
 163 int
 164 check_connection_completion(int fd)
 165 {
 166     struct pollfd pfd;
 167     int retval;
 168
 169     pfd.fd = fd;
 170     pfd.events = POLLOUT;
 171     do {
 172         retval = poll(&pfd, 1, 0);
 173     } while (retval < 0 && errno == EINTR);
 174     if (retval == 1) {
 175         return get_socket_error(fd);
 176     } else if (retval < 0) {
 177         static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(5, 10);
 178         VLOG_ERR_RL(&rl, "poll: %s", strerror(errno));
 179         return errno;
 180     } else {
 181         return EAGAIN;
 182     }
 183 }
 184
 185 /* Drain all the data currently in the receive queue of a datagram socket (and
 186  * possibly additional data).  There is no way to know how many packets are in
 187  * the receive queue, but we do know that the total number of bytes queued does
 188  * not exceed the receive buffer size, so we pull packets until none are left
 189  * or we've read that many bytes. */
 190 int
 191 drain_rcvbuf(int fd)
 192 {
 193     socklen_t rcvbuf_len;
 194     size_t rcvbuf;
 195
 196     rcvbuf_len = sizeof rcvbuf;
 197     if (getsockopt(fd, SOL_SOCKET, SO_RCVBUF, &rcvbuf, &rcvbuf_len) < 0) {
 198         static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(5, 10);
 199         VLOG_ERR_RL(&rl, "getsockopt(SO_RCVBUF) failed: %s", strerror(errno));
 200         return errno;
 201     }
 202     while (rcvbuf > 0) {
 203         /* In Linux, specifying MSG_TRUNC in the flags argument causes the
 204          * datagram length to be returned, even if that is longer than the
 205          * buffer provided.  Thus, we can use a 1-byte buffer to discard the
 206          * incoming datagram and still be able to account how many bytes were
 207          * removed from the receive buffer.
 208          *
 209          * On other Unix-like OSes, MSG_TRUNC has no effect in the flags
 210          * argument. */
 211         char buffer[LINUX ? 1 : 2048];
 212         ssize_t n_bytes = recv(fd, buffer, sizeof buffer,
 213                                MSG_TRUNC | MSG_DONTWAIT);
 214         if (n_bytes <= 0 || n_bytes >= rcvbuf) {
 215             break;
 216         }
 217         rcvbuf -= n_bytes;
 218     }
 219     return 0;
 220 }
 221
 222 /* Reads and discards up to 'n' datagrams from 'fd', stopping as soon as no
 223  * more data can be immediately read.  ('fd' should therefore be in
 224  * non-blocking mode.)*/
 225 void
 226 drain_fd(int fd, size_t n_packets)
 227 {
 228     for (; n_packets > 0; n_packets--) {
 229         /* 'buffer' only needs to be 1 byte long in most circumstances.  This
 230          * size is defensive against the possibility that we someday want to
 231          * use a Linux tap device without TUN_NO_PI, in which case a buffer
 232          * smaller than sizeof(struct tun_pi) will give EINVAL on read. */
 233         char buffer[128];
 234         if (read(fd, buffer, sizeof buffer) <= 0) {
 235             break;
 236         }
 237     }
 238 }
 239
 240 /* Stores in '*un' a sockaddr_un that refers to file 'name'.  Stores in
 241  * '*un_len' the size of the sockaddr_un. */
 242 static void
 243 make_sockaddr_un__(const char *name, struct sockaddr_un *un, socklen_t *un_len)
 244 {
 245     un->sun_family = AF_UNIX;
 246     ovs_strzcpy(un->sun_path, name, sizeof un->sun_path);
 247     *un_len = (offsetof(struct sockaddr_un, sun_path)
 248                 + strlen (un->sun_path) + 1);
 249 }
 250
 251 /* Stores in '*un' a sockaddr_un that refers to file 'name'.  Stores in
 252  * '*un_len' the size of the sockaddr_un.
 253  *
 254  * Returns 0 on success, otherwise a positive errno value.  On success,
 255  * '*dirfdp' is either -1 or a nonnegative file descriptor that the caller
 256  * should close after using '*un' to bind or connect.  On failure, '*dirfdp' is
 257  * -1. */
 258 static int
 259 make_sockaddr_un(const char *name, struct sockaddr_un *un, socklen_t *un_len,
 260                  int *dirfdp)
 261 {
 262     enum { MAX_UN_LEN = sizeof un->sun_path - 1 };
 263
 264     *dirfdp = -1;
 265     if (strlen(name) > MAX_UN_LEN) {
 266         static struct vlog_rate_limit rl = VLOG_RATE_LIMIT_INIT(1, 1);
 267
 268         if (LINUX) {
 269             /* 'name' is too long to fit in a sockaddr_un, but we have a
 270              * workaround for that on Linux: shorten it by opening a file
 271              * descriptor for the directory part of the name and indirecting
 272              * through /proc/self/fd/<dirfd>/<basename>. */
 273             char *dir, *base;
 274             char *short_name;
 275             int dirfd;
 276
 277             dir = dir_name(name);
 278             base = base_name(name);
 279
 280             dirfd = open(dir, O_DIRECTORY | O_RDONLY);
 281             if (dirfd < 0) {
 282                 free(base);
 283                 free(dir);
 284                 return errno;
 285             }
 286
 287             short_name = xasprintf("/proc/self/fd/%d/%s", dirfd, base);
 288             free(dir);
 289             free(base);
 290
 291             if (strlen(short_name) <= MAX_UN_LEN) {
 292                 make_sockaddr_un__(short_name, un, un_len);
 293                 free(short_name);
 294                 *dirfdp = dirfd;
 295                 return 0;
 296             }
 297             free(short_name);
 298             close(dirfd);
 299
 300             VLOG_WARN_RL(&rl, "Unix socket name %s is longer than maximum "
 301                          "%d bytes (even shortened)", name, MAX_UN_LEN);
 302         } else {
 303             /* 'name' is too long and we have no workaround. */
 304             VLOG_WARN_RL(&rl, "Unix socket name %s is longer than maximum "
 305                          "%d bytes", name, MAX_UN_LEN);
 306         }
 307
 308         return ENAMETOOLONG;
 309     } else {
 310         make_sockaddr_un__(name, un, un_len);
 311         return 0;
 312     }
 313 }
 314
 315 /* Binds Unix domain socket 'fd' to a file with permissions 0700. */
 316 static int
 317 bind_unix_socket(int fd, struct sockaddr *sun, socklen_t sun_len)
 318 {
 319     /* According to _Unix Network Programming_, umask should affect bind(). */
 320     mode_t old_umask = umask(0077);
 321     int error = bind(fd, sun, sun_len) ? errno : 0;
 322     umask(old_umask);
 323     return error;
 324 }
 325
 326 /* Creates a Unix domain socket in the given 'style' (either SOCK_DGRAM or
 327  * SOCK_STREAM) that is bound to '*bind_path' (if 'bind_path' is non-null) and
 328  * connected to '*connect_path' (if 'connect_path' is non-null).  If 'nonblock'
 329  * is true, the socket is made non-blocking.  If 'passcred' is true, the socket
 330  * is configured to receive SCM_CREDENTIALS control messages.
 331  *
 332  * Returns the socket's fd if successful, otherwise a negative errno value. */
 333 int
 334 make_unix_socket(int style, bool nonblock, bool passcred OVS_UNUSED,
 335                  const char *bind_path, const char *connect_path)
 336 {
 337     int error;
 338     int fd;
 339
 340     fd = socket(PF_UNIX, style, 0);
 341     if (fd < 0) {
 342         return -errno;
 343     }
 344
 345     /* Set nonblocking mode right away, if we want it.  This prevents blocking
 346      * in connect(), if connect_path != NULL.  (In turn, that's a corner case:
 347      * it will only happen if style is SOCK_STREAM or SOCK_SEQPACKET, and only
 348      * if a backlog of un-accepted connections has built up in the kernel.)  */
 349     if (nonblock) {
 350         int flags = fcntl(fd, F_GETFL, 0);
 351         if (flags == -1) {
 352             error = errno;
 353             goto error;
 354         }
 355         if (fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1) {
 356             error = errno;
 357             goto error;
 358         }
 359     }
 360
 361     if (bind_path) {
 362         struct sockaddr_un un;
 363         socklen_t un_len;
 364         int dirfd;
 365
 366         if (unlink(bind_path) && errno != ENOENT) {
 367             VLOG_WARN("unlinking \"%s\": %s\n", bind_path, strerror(errno));
 368         }
 369         fatal_signal_add_file_to_unlink(bind_path);
 370
 371         error = make_sockaddr_un(bind_path, &un, &un_len, &dirfd);
 372         if (!error) {
 373             error = bind_unix_socket(fd, (struct sockaddr *) &un, un_len);
 374         }
 375         if (dirfd >= 0) {
 376             close(dirfd);
 377         }
 378         if (error) {
 379             goto error;
 380         }
 381     }
 382
 383     if (connect_path) {
 384         struct sockaddr_un un;
 385         socklen_t un_len;
 386         int dirfd;
 387
 388         error = make_sockaddr_un(connect_path, &un, &un_len, &dirfd);
 389         if (!error
 390             && connect(fd, (struct sockaddr*) &un, un_len)
 391             && errno != EINPROGRESS) {
 392             error = errno;
 393         }
 394         if (dirfd >= 0) {
 395             close(dirfd);
 396         }
 397         if (error) {
 398             goto error;
 399         }
 400     }
 401
 402 #ifdef SCM_CREDENTIALS
 403     if (passcred) {
 404         int enable = 1;
 405         if (setsockopt(fd, SOL_SOCKET, SO_PASSCRED, &enable, sizeof(enable))) {
 406             error = errno;
 407             goto error;
 408         }
 409     }
 410 #endif
 411
 412     return fd;
 413
 414 error:
 415     if (error == EAGAIN) {
 416         error = EPROTO;
 417     }
 418     if (bind_path) {
 419         fatal_signal_remove_file_to_unlink(bind_path);
 420     }
 421     close(fd);
 422     return -error;
 423 }
 424
 425 int
 426 get_unix_name_len(socklen_t sun_len)
 427 {
 428     return (sun_len >= offsetof(struct sockaddr_un, sun_path)
 429             ? sun_len - offsetof(struct sockaddr_un, sun_path)
 430             : 0);
 431 }
 432
 433 ovs_be32
 434 guess_netmask(ovs_be32 ip_)
 435 {
 436     uint32_t ip = ntohl(ip_);
 437     return ((ip >> 31) == 0 ? htonl(0xff000000)   /* Class A */
 438             : (ip >> 30) == 2 ? htonl(0xffff0000) /* Class B */
 439             : (ip >> 29) == 6 ? htonl(0xffffff00) /* Class C */
 440             : htonl(0));                          /* ??? */
 441 }
 442
 443 /* Parses 'target', which should be a string in the format "<host>[:<port>]".
 444  * <host> is required.  If 'default_port' is nonzero then <port> is optional
 445  * and defaults to 'default_port'.
 446  *
 447  * On success, returns true and stores the parsed remote address into '*sinp'.
 448  * On failure, logs an error, stores zeros into '*sinp', and returns false. */
 449 bool
 450 inet_parse_active(const char *target_, uint16_t default_port,
 451                   struct sockaddr_in *sinp)
 452 {
 453     char *target = xstrdup(target_);
 454     char *save_ptr = NULL;
 455     const char *host_name;
 456     const char *port_string;
 457     bool ok = false;
 458
 459     /* Defaults. */
 460     sinp->sin_family = AF_INET;
 461     sinp->sin_port = htons(default_port);
 462
 463     /* Tokenize. */
 464     host_name = strtok_r(target, ":", &save_ptr);
 465     port_string = strtok_r(NULL, ":", &save_ptr);
 466     if (!host_name) {
 467         VLOG_ERR("%s: bad peer name format", target_);
 468         goto exit;
 469     }
 470
 471     /* Look up IP, port. */
 472     if (lookup_ip(host_name, &sinp->sin_addr)) {
 473         goto exit;
 474     }
 475     if (port_string && atoi(port_string)) {
 476         sinp->sin_port = htons(atoi(port_string));
 477     } else if (!default_port) {
 478         VLOG_ERR("%s: port number must be specified", target_);
 479         goto exit;
 480     }
 481
 482     ok = true;
 483
 484 exit:
 485     if (!ok) {
 486         memset(sinp, 0, sizeof *sinp);
 487     }
 488     free(target);
 489     return ok;
 490 }
 491
 492 /* Opens a non-blocking IPv4 socket of the specified 'style' and connects to
 493  * 'target', which should be a string in the format "<host>[:<port>]".  <host>
 494  * is required.  If 'default_port' is nonzero then <port> is optional and
 495  * defaults to 'default_port'.
 496  *
 497  * 'style' should be SOCK_STREAM (for TCP) or SOCK_DGRAM (for UDP).
 498  *
 499  * On success, returns 0 (indicating connection complete) or EAGAIN (indicating
 500  * connection in progress), in which case the new file descriptor is stored
 501  * into '*fdp'.  On failure, returns a positive errno value other than EAGAIN
 502  * and stores -1 into '*fdp'.
 503  *
 504  * If 'sinp' is non-null, then on success the target address is stored into
 505  * '*sinp'. */
 506 int
 507 inet_open_active(int style, const char *target, uint16_t default_port,
 508                  struct sockaddr_in *sinp, int *fdp)
 509 {
 510     struct sockaddr_in sin;
 511     int fd = -1;
 512     int error;
 513
 514     /* Parse. */
 515     if (!inet_parse_active(target, default_port, &sin)) {
 516         error = EAFNOSUPPORT;
 517         goto exit;
 518     }
 519
 520     /* Create non-blocking socket. */
 521     fd = socket(AF_INET, style, 0);
 522     if (fd < 0) {
 523         VLOG_ERR("%s: socket: %s", target, strerror(errno));
 524         error = errno;
 525         goto exit;
 526     }
 527     error = set_nonblocking(fd);
 528     if (error) {
 529         goto exit_close;
 530     }
 531
 532     /* Connect. */
 533     error = connect(fd, (struct sockaddr *) &sin, sizeof sin) == 0 ? 0 : errno;
 534     if (error == EINPROGRESS) {
 535         error = EAGAIN;
 536     } else if (error && error != EAGAIN) {
 537         goto exit_close;
 538     }
 539
 540     /* Success: error is 0 or EAGAIN. */
 541     goto exit;
 542
 543 exit_close:
 544     close(fd);
 545 exit:
 546     if (!error || error == EAGAIN) {
 547         if (sinp) {
 548             *sinp = sin;
 549         }
 550         *fdp = fd;
 551     } else {
 552         *fdp = -1;
 553     }
 554     return error;
 555 }
 556
 557 /* Opens a non-blocking IPv4 socket of the specified 'style', binds to
 558  * 'target', and listens for incoming connections.  'target' should be a string
 559  * in the format "[<port>][:<ip>]":
 560  *
 561  *      - If 'default_port' is -1, then <port> is required.  Otherwise, if
 562  *        <port> is omitted, then 'default_port' is used instead.
 563  *
 564  *      - If <port> (or 'default_port', if used) is 0, then no port is bound
 565  *        and the TCP/IP stack will select a port.
 566  *
 567  *      - If <ip> is omitted then the IP address is wildcarded.
 568  *
 569  * 'style' should be SOCK_STREAM (for TCP) or SOCK_DGRAM (for UDP).
 570  *
 571  * For TCP, the socket will have SO_REUSEADDR turned on.
 572  *
 573  * On success, returns a non-negative file descriptor.  On failure, returns a
 574  * negative errno value.
 575  *
 576  * If 'sinp' is non-null, then on success the bound address is stored into
 577  * '*sinp'. */
 578 int
 579 inet_open_passive(int style, const char *target_, int default_port,
 580                   struct sockaddr_in *sinp)
 581 {
 582     char *target = xstrdup(target_);
 583     char *string_ptr = target;
 584     struct sockaddr_in sin;
 585     const char *host_name;
 586     const char *port_string;
 587     int fd = 0, error, port;
 588     unsigned int yes  = 1;
 589
 590     /* Address defaults. */
 591     memset(&sin, 0, sizeof sin);
 592     sin.sin_family = AF_INET;
 593     sin.sin_addr.s_addr = htonl(INADDR_ANY);
 594     sin.sin_port = htons(default_port);
 595
 596     /* Parse optional port number. */
 597     port_string = strsep(&string_ptr, ":");
 598     if (port_string && str_to_int(port_string, 10, &port)) {
 599         sin.sin_port = htons(port);
 600     } else if (default_port < 0) {
 601         VLOG_ERR("%s: port number must be specified", target_);
 602         error = EAFNOSUPPORT;
 603         goto exit;
 604     }
 605
 606     /* Parse optional bind IP. */
 607     host_name = strsep(&string_ptr, ":");
 608     if (host_name && host_name[0]) {
 609         error = lookup_ip(host_name, &sin.sin_addr);
 610         if (error) {
 611             goto exit;
 612         }
 613     }
 614
 615     /* Create non-blocking socket, set SO_REUSEADDR. */
 616     fd = socket(AF_INET, style, 0);
 617     if (fd < 0) {
 618         error = errno;
 619         VLOG_ERR("%s: socket: %s", target_, strerror(error));
 620         goto exit;
 621     }
 622     error = set_nonblocking(fd);
 623     if (error) {
 624         goto exit_close;
 625     }
 626     if (style == SOCK_STREAM
 627         && setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof yes) < 0) {
 628         error = errno;
 629         VLOG_ERR("%s: setsockopt(SO_REUSEADDR): %s", target_, strerror(error));
 630         goto exit_close;
 631     }
 632
 633     /* Bind. */
 634     if (bind(fd, (struct sockaddr *) &sin, sizeof sin) < 0) {
 635         error = errno;
 636         VLOG_ERR("%s: bind: %s", target_, strerror(error));
 637         goto exit_close;
 638     }
 639
 640     /* Listen. */
 641     if (listen(fd, 10) < 0) {
 642         error = errno;
 643         VLOG_ERR("%s: listen: %s", target_, strerror(error));
 644         goto exit_close;
 645     }
 646
 647     if (sinp) {
 648         socklen_t sin_len = sizeof sin;
 649         if (getsockname(fd, (struct sockaddr *) &sin, &sin_len) < 0){
 650             error = errno;
 651             VLOG_ERR("%s: getsockname: %s", target_, strerror(error));
 652             goto exit_close;
 653         }
 654         if (sin.sin_family != AF_INET || sin_len != sizeof sin) {
 655             VLOG_ERR("%s: getsockname: invalid socket name", target_);
 656             goto exit_close;
 657         }
 658         *sinp = sin;
 659     }
 660
 661     error = 0;
 662     goto exit;
 663
 664 exit_close:
 665     close(fd);
 666 exit:
 667     free(target);
 668     return error ? -error : fd;
 669 }
 670
 671 /* Returns a readable and writable fd for /dev/null, if successful, otherwise
 672  * a negative errno value.  The caller must not close the returned fd (because
 673  * the same fd will be handed out to subsequent callers). */
 674 int
 675 get_null_fd(void)
 676 {
 677     static int null_fd = -1;
 678     if (null_fd < 0) {
 679         null_fd = open("/dev/null", O_RDWR);
 680         if (null_fd < 0) {
 681             int error = errno;
 682             VLOG_ERR("could not open /dev/null: %s", strerror(error));
 683             return -error;
 684         }
 685     }
 686     return null_fd;
 687 }
 688
 689 int
 690 read_fully(int fd, void *p_, size_t size, size_t *bytes_read)
 691 {
 692     uint8_t *p = p_;
 693
 694     *bytes_read = 0;
 695     while (size > 0) {
 696         ssize_t retval = read(fd, p, size);
 697         if (retval > 0) {
 698             *bytes_read += retval;
 699             size -= retval;
 700             p += retval;
 701         } else if (retval == 0) {
 702             return EOF;
 703         } else if (errno != EINTR) {
 704             return errno;
 705         }
 706     }
 707     return 0;
 708 }
 709
 710 int
 711 write_fully(int fd, const void *p_, size_t size, size_t *bytes_written)
 712 {
 713     const uint8_t *p = p_;
 714
 715     *bytes_written = 0;
 716     while (size > 0) {
 717         ssize_t retval = write(fd, p, size);
 718         if (retval > 0) {
 719             *bytes_written += retval;
 720             size -= retval;
 721             p += retval;
 722         } else if (retval == 0) {
 723             VLOG_WARN("write returned 0");
 724             return EPROTO;
 725         } else if (errno != EINTR) {
 726             return errno;
 727         }
 728     }
 729     return 0;
 730 }
 731
 732 /* Given file name 'file_name', fsyncs the directory in which it is contained.
 733  * Returns 0 if successful, otherwise a positive errno value. */
 734 int
 735 fsync_parent_dir(const char *file_name)
 736 {
 737     int error = 0;
 738     char *dir;
 739     int fd;
 740
 741     dir = dir_name(file_name);
 742     fd = open(dir, O_RDONLY);
 743     if (fd >= 0) {
 744         if (fsync(fd)) {
 745             if (errno == EINVAL || errno == EROFS) {
 746                 /* This directory does not support synchronization.  Not
 747                  * really an error. */
 748             } else {
 749                 error = errno;
 750                 VLOG_ERR("%s: fsync failed (%s)", dir, strerror(error));
 751             }
 752         }
 753         close(fd);
 754     } else {
 755         error = errno;
 756         VLOG_ERR("%s: open failed (%s)", dir, strerror(error));
 757     }
 758     free(dir);
 759
 760     return error;
 761 }
 762
 763 /* Obtains the modification time of the file named 'file_name' to the greatest
 764  * supported precision.  If successful, stores the mtime in '*mtime' and
 765  * returns 0.  On error, returns a positive errno value and stores zeros in
 766  * '*mtime'. */
 767 int
 768 get_mtime(const char *file_name, struct timespec *mtime)
 769 {
 770     struct stat s;
 771
 772     if (!stat(file_name, &s)) {
 773         mtime->tv_sec = s.st_mtime;
 774
 775 #if HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC
 776         mtime->tv_nsec = s.st_mtim.tv_nsec;
 777 #elif HAVE_STRUCT_STAT_ST_MTIMENSEC
 778         mtime->tv_nsec = s.st_mtimensec;
 779 #else
 780         mtime->tv_nsec = 0;
 781 #endif
 782
 783         return 0;
 784     } else {
 785         mtime->tv_sec = mtime->tv_nsec = 0;
 786         return errno;
 787     }
 788 }
 789
 790 void
 791 xpipe(int fds[2])
 792 {
 793     if (pipe(fds)) {
 794         VLOG_FATAL("failed to create pipe (%s)", strerror(errno));
 795     }
 796 }
 797
 798 static int
 799 getsockopt_int(int fd, int level, int optname, int *valuep)
 800 {
 801     socklen_t len = sizeof *valuep;
 802
 803     return (getsockopt(fd, level, optname, valuep, &len) ? errno
 804             : len == sizeof *valuep ? 0
 805             : EINVAL);
 806 }
 807
 808 static void
 809 describe_sockaddr(struct ds *string, int fd,
 810                   int (*getaddr)(int, struct sockaddr *, socklen_t *))
 811 {
 812     struct sockaddr_storage ss;
 813     socklen_t len = sizeof ss;
 814
 815     if (!getaddr(fd, (struct sockaddr *) &ss, &len)) {
 816         if (ss.ss_family == AF_INET) {
 817             struct sockaddr_in sin;
 818
 819             memcpy(&sin, &ss, sizeof sin);
 820             ds_put_format(string, IP_FMT":%"PRIu16,
 821                           IP_ARGS(&sin.sin_addr.s_addr), ntohs(sin.sin_port));
 822         } else if (ss.ss_family == AF_UNIX) {
 823             struct sockaddr_un sun;
 824             const char *null;
 825             size_t maxlen;
 826
 827             memcpy(&sun, &ss, sizeof sun);
 828             maxlen = len - offsetof(struct sockaddr_un, sun_path);
 829             null = memchr(sun.sun_path, '\0', maxlen);
 830             ds_put_buffer(string, sun.sun_path,
 831                           null ? null - sun.sun_path : maxlen);
 832         }
 833 #ifdef HAVE_NETLINK
 834         else if (ss.ss_family == AF_NETLINK) {
 835             int protocol;
 836
 837 /* SO_PROTOCOL was introduced in 2.6.32.  Support it regardless of the version
 838  * of the Linux kernel headers in use at build time. */
 839 #ifndef SO_PROTOCOL
 840 #define SO_PROTOCOL 38
 841 #endif
 842
 843             if (!getsockopt_int(fd, SOL_SOCKET, SO_PROTOCOL, &protocol)) {
 844                 switch (protocol) {
 845                 case NETLINK_ROUTE:
 846                     ds_put_cstr(string, "NETLINK_ROUTE");
 847                     break;
 848
 849                 case NETLINK_GENERIC:
 850                     ds_put_cstr(string, "NETLINK_GENERIC");
 851                     break;
 852
 853                 default:
 854                     ds_put_format(string, "AF_NETLINK family %d", protocol);
 855                     break;
 856                 }
 857             } else {
 858                 ds_put_cstr(string, "AF_NETLINK");
 859             }
 860         }
 861 #endif
 862 #if AF_PACKET && __linux__
 863         else if (ss.ss_family == AF_PACKET) {
 864             struct sockaddr_ll sll;
 865
 866             memcpy(&sll, &ss, sizeof sll);
 867             ds_put_cstr(string, "AF_PACKET");
 868             if (sll.sll_ifindex) {
 869                 char name[IFNAMSIZ];
 870
 871                 if (if_indextoname(sll.sll_ifindex, name)) {
 872                     ds_put_format(string, "(%s)", name);
 873                 } else {
 874                     ds_put_format(string, "(ifindex=%d)", sll.sll_ifindex);
 875                 }
 876             }
 877             if (sll.sll_protocol) {
 878                 ds_put_format(string, "(protocol=0x%"PRIu16")",
 879                               ntohs(sll.sll_protocol));
 880             }
 881         }
 882 #endif
 883         else if (ss.ss_family == AF_UNSPEC) {
 884             ds_put_cstr(string, "AF_UNSPEC");
 885         } else {
 886             ds_put_format(string, "AF_%d", (int) ss.ss_family);
 887         }
 888     }
 889 }
 890
 891
 892 #ifdef __linux__
 893 static void
 894 put_fd_filename(struct ds *string, int fd)
 895 {
 896     char buf[1024];
 897     char *linkname;
 898     int n;
 899
 900     linkname = xasprintf("/proc/self/fd/%d", fd);
 901     n = readlink(linkname, buf, sizeof buf);
 902     if (n > 0) {
 903         ds_put_char(string, ' ');
 904         ds_put_buffer(string, buf, n);
 905         if (n > sizeof buf) {
 906             ds_put_cstr(string, "...");
 907         }
 908     }
 909     free(linkname);
 910 }
 911 #endif
 912
 913 /* Returns a malloc()'d string describing 'fd', for use in logging. */
 914 char *
 915 describe_fd(int fd)
 916 {
 917     struct ds string;
 918     struct stat s;
 919
 920     ds_init(&string);
 921     if (fstat(fd, &s)) {
 922         ds_put_format(&string, "fstat failed (%s)", strerror(errno));
 923     } else if (S_ISSOCK(s.st_mode)) {
 924         describe_sockaddr(&string, fd, getsockname);
 925         ds_put_cstr(&string, "<->");
 926         describe_sockaddr(&string, fd, getpeername);
 927     } else {
 928         ds_put_cstr(&string, (isatty(fd) ? "tty"
 929                               : S_ISDIR(s.st_mode) ? "directory"
 930                               : S_ISCHR(s.st_mode) ? "character device"
 931                               : S_ISBLK(s.st_mode) ? "block device"
 932                               : S_ISREG(s.st_mode) ? "file"
 933                               : S_ISFIFO(s.st_mode) ? "FIFO"
 934                               : S_ISLNK(s.st_mode) ? "symbolic link"
 935                               : "unknown"));
 936 #ifdef __linux__
 937         put_fd_filename(&string, fd);
 938 #endif
 939     }
 940     return ds_steal_cstr(&string);
 941 }