lib/process.c

   1 /*
   2  * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013 Nicira, Inc.
   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 "process.h"
  19 #include <errno.h>
  20 #include <fcntl.h>
  21 #include <signal.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <sys/stat.h>
  25 #include <sys/wait.h>
  26 #include <unistd.h>
  27 #include "coverage.h"
  28 #include "dynamic-string.h"
  29 #include "fatal-signal.h"
  30 #include "list.h"
  31 #include "poll-loop.h"
  32 #include "signals.h"
  33 #include "socket-util.h"
  34 #include "util.h"
  35 #include "vlog.h"
  36
  37 VLOG_DEFINE_THIS_MODULE(process);
  38
  39 COVERAGE_DEFINE(process_run);
  40 COVERAGE_DEFINE(process_run_capture);
  41 COVERAGE_DEFINE(process_sigchld);
  42 COVERAGE_DEFINE(process_start);
  43
  44 struct process {
  45     struct list node;
  46     char *name;
  47     pid_t pid;
  48
  49     /* Modified by signal handler. */
  50     volatile bool exited;
  51     volatile int status;
  52 };
  53
  54 /* Pipe used to signal child termination. */
  55 static int fds[2];
  56
  57 /* All processes. */
  58 static struct list all_processes = LIST_INITIALIZER(&all_processes);
  59
  60 static bool sigchld_is_blocked(void);
  61 static void block_sigchld(sigset_t *);
  62 static void unblock_sigchld(const sigset_t *);
  63 static void sigchld_handler(int signr OVS_UNUSED);
  64 static bool is_member(int x, const int *array, size_t);
  65
  66 /* Initializes the process subsystem (if it is not already initialized).  Calls
  67  * exit() if initialization fails.
  68  *
  69  * Calling this function is optional; it will be called automatically by
  70  * process_start() if necessary.  Calling it explicitly allows the client to
  71  * prevent the process from exiting at an unexpected time. */
  72 void
  73 process_init(void)
  74 {
  75     static bool inited;
  76     struct sigaction sa;
  77
  78     if (inited) {
  79         return;
  80     }
  81     inited = true;
  82
  83     /* Create notification pipe. */
  84     xpipe_nonblocking(fds);
  85
  86     /* Set up child termination signal handler. */
  87     memset(&sa, 0, sizeof sa);
  88     sa.sa_handler = sigchld_handler;
  89     sigemptyset(&sa.sa_mask);
  90     sa.sa_flags = SA_NOCLDSTOP | SA_RESTART;
  91     xsigaction(SIGCHLD, &sa, NULL);
  92 }
  93
  94 char *
  95 process_escape_args(char **argv)
  96 {
  97     struct ds ds = DS_EMPTY_INITIALIZER;
  98     char **argp;
  99     for (argp = argv; *argp; argp++) {
 100         const char *arg = *argp;
 101         const char *p;
 102         if (argp != argv) {
 103             ds_put_char(&ds, ' ');
 104         }
 105         if (arg[strcspn(arg, " \t\r\n\v\\\'\"")]) {
 106             ds_put_char(&ds, '"');
 107             for (p = arg; *p; p++) {
 108                 if (*p == '\\' || *p == '\"') {
 109                     ds_put_char(&ds, '\\');
 110                 }
 111                 ds_put_char(&ds, *p);
 112             }
 113             ds_put_char(&ds, '"');
 114         } else {
 115             ds_put_cstr(&ds, arg);
 116         }
 117     }
 118     return ds_cstr(&ds);
 119 }
 120
 121 /* Prepare to start a process whose command-line arguments are given by the
 122  * null-terminated 'argv' array.  Returns 0 if successful, otherwise a
 123  * positive errno value. */
 124 static int
 125 process_prestart(char **argv)
 126 {
 127     char *binary;
 128
 129     process_init();
 130
 131     /* Log the process to be started. */
 132     if (VLOG_IS_DBG_ENABLED()) {
 133         char *args = process_escape_args(argv);
 134         VLOG_DBG("starting subprocess: %s", args);
 135         free(args);
 136     }
 137
 138     /* execvp() will search PATH too, but the error in that case is more
 139      * obscure, since it is only reported post-fork. */
 140     binary = process_search_path(argv[0]);
 141     if (!binary) {
 142         VLOG_ERR("%s not found in PATH", argv[0]);
 143         return ENOENT;
 144     }
 145     free(binary);
 146
 147     return 0;
 148 }
 149
 150 /* Creates and returns a new struct process with the specified 'name' and
 151  * 'pid'.
 152  *
 153  * This is racy unless SIGCHLD is blocked (and has been blocked since before
 154  * the fork()) that created the subprocess.  */
 155 static struct process *
 156 process_register(const char *name, pid_t pid)
 157 {
 158     struct process *p;
 159     const char *slash;
 160
 161     ovs_assert(sigchld_is_blocked());
 162
 163     p = xzalloc(sizeof *p);
 164     p->pid = pid;
 165     slash = strrchr(name, '/');
 166     p->name = xstrdup(slash ? slash + 1 : name);
 167     p->exited = false;
 168
 169     list_push_back(&all_processes, &p->node);
 170
 171     return p;
 172 }
 173
 174 /* Starts a subprocess with the arguments in the null-terminated argv[] array.
 175  * argv[0] is used as the name of the process.  Searches the PATH environment
 176  * variable to find the program to execute.
 177  *
 178  * All file descriptors are closed before executing the subprocess, except for
 179  * fds 0, 1, and 2 and the 'n_keep_fds' fds listed in 'keep_fds'.  Also, any of
 180  * the 'n_null_fds' fds listed in 'null_fds' are replaced by /dev/null.
 181  *
 182  * Returns 0 if successful, otherwise a positive errno value indicating the
 183  * error.  If successful, '*pp' is assigned a new struct process that may be
 184  * used to query the process's status.  On failure, '*pp' is set to NULL. */
 185 int
 186 process_start(char **argv,
 187               const int keep_fds[], size_t n_keep_fds,
 188               const int null_fds[], size_t n_null_fds,
 189               struct process **pp)
 190 {
 191     sigset_t oldsigs;
 192     int nullfd;
 193     pid_t pid;
 194     int error;
 195
 196     *pp = NULL;
 197     COVERAGE_INC(process_start);
 198     error = process_prestart(argv);
 199     if (error) {
 200         return error;
 201     }
 202
 203     if (n_null_fds) {
 204         nullfd = get_null_fd();
 205         if (nullfd < 0) {
 206             return -nullfd;
 207         }
 208     } else {
 209         nullfd = -1;
 210     }
 211
 212     block_sigchld(&oldsigs);
 213     pid = fork();
 214     if (pid < 0) {
 215         unblock_sigchld(&oldsigs);
 216         VLOG_WARN("fork failed: %s", strerror(errno));
 217         return errno;
 218     } else if (pid) {
 219         /* Running in parent process. */
 220         *pp = process_register(argv[0], pid);
 221         unblock_sigchld(&oldsigs);
 222         return 0;
 223     } else {
 224         /* Running in child process. */
 225         int fd_max = get_max_fds();
 226         int fd;
 227
 228         fatal_signal_fork();
 229         unblock_sigchld(&oldsigs);
 230         for (fd = 0; fd < fd_max; fd++) {
 231             if (is_member(fd, null_fds, n_null_fds)) {
 232                 dup2(nullfd, fd);
 233             } else if (fd >= 3 && fd != nullfd
 234                        && !is_member(fd, keep_fds, n_keep_fds)) {
 235                 close(fd);
 236             }
 237         }
 238         if (nullfd >= 0
 239             && !is_member(nullfd, keep_fds, n_keep_fds)
 240             && !is_member(nullfd, null_fds, n_null_fds)) {
 241             close(nullfd);
 242         }
 243         execvp(argv[0], argv);
 244         fprintf(stderr, "execvp(\"%s\") failed: %s\n",
 245                 argv[0], strerror(errno));
 246         _exit(1);
 247     }
 248 }
 249
 250 /* Destroys process 'p'. */
 251 void
 252 process_destroy(struct process *p)
 253 {
 254     if (p) {
 255         sigset_t oldsigs;
 256
 257         block_sigchld(&oldsigs);
 258         list_remove(&p->node);
 259         unblock_sigchld(&oldsigs);
 260
 261         free(p->name);
 262         free(p);
 263     }
 264 }
 265
 266 /* Sends signal 'signr' to process 'p'.  Returns 0 if successful, otherwise a
 267  * positive errno value. */
 268 int
 269 process_kill(const struct process *p, int signr)
 270 {
 271     return (p->exited ? ESRCH
 272             : !kill(p->pid, signr) ? 0
 273             : errno);
 274 }
 275
 276 /* Returns the pid of process 'p'. */
 277 pid_t
 278 process_pid(const struct process *p)
 279 {
 280     return p->pid;
 281 }
 282
 283 /* Returns the name of process 'p' (the name passed to process_start() with any
 284  * leading directories stripped). */
 285 const char *
 286 process_name(const struct process *p)
 287 {
 288     return p->name;
 289 }
 290
 291 /* Returns true if process 'p' has exited, false otherwise. */
 292 bool
 293 process_exited(struct process *p)
 294 {
 295     if (p->exited) {
 296         return true;
 297     } else {
 298         char buf[_POSIX_PIPE_BUF];
 299         ignore(read(fds[0], buf, sizeof buf));
 300         return false;
 301     }
 302 }
 303
 304 /* Returns process 'p''s exit status, as reported by waitpid(2).
 305  * process_status(p) may be called only after process_exited(p) has returned
 306  * true. */
 307 int
 308 process_status(const struct process *p)
 309 {
 310     ovs_assert(p->exited);
 311     return p->status;
 312 }
 313
 314 int
 315 process_run(char **argv,
 316             const int keep_fds[], size_t n_keep_fds,
 317             const int null_fds[], size_t n_null_fds,
 318             int *status)
 319 {
 320     struct process *p;
 321     int retval;
 322
 323     COVERAGE_INC(process_run);
 324     retval = process_start(argv, keep_fds, n_keep_fds, null_fds, n_null_fds,
 325                            &p);
 326     if (retval) {
 327         *status = 0;
 328         return retval;
 329     }
 330
 331     while (!process_exited(p)) {
 332         process_wait(p);
 333         poll_block();
 334     }
 335     *status = process_status(p);
 336     process_destroy(p);
 337     return 0;
 338 }
 339
 340 /* Given 'status', which is a process status in the form reported by waitpid(2)
 341  * and returned by process_status(), returns a string describing how the
 342  * process terminated.  The caller is responsible for freeing the string when
 343  * it is no longer needed. */
 344 char *
 345 process_status_msg(int status)
 346 {
 347     struct ds ds = DS_EMPTY_INITIALIZER;
 348     if (WIFEXITED(status)) {
 349         ds_put_format(&ds, "exit status %d", WEXITSTATUS(status));
 350     } else if (WIFSIGNALED(status)) {
 351         ds_put_format(&ds, "killed (%s)", signal_name(WTERMSIG(status)));
 352     } else if (WIFSTOPPED(status)) {
 353         ds_put_format(&ds, "stopped (%s)", signal_name(WSTOPSIG(status)));
 354     } else {
 355         ds_put_format(&ds, "terminated abnormally (%x)", status);
 356     }
 357     if (WCOREDUMP(status)) {
 358         ds_put_cstr(&ds, ", core dumped");
 359     }
 360     return ds_cstr(&ds);
 361 }
 362
 363 /* Causes the next call to poll_block() to wake up when process 'p' has
 364  * exited. */
 365 void
 366 process_wait(struct process *p)
 367 {
 368     if (p->exited) {
 369         poll_immediate_wake();
 370     } else {
 371         poll_fd_wait(fds[0], POLLIN);
 372     }
 373 }
 374
 375 char *
 376 process_search_path(const char *name)
 377 {
 378     char *save_ptr = NULL;
 379     char *path, *dir;
 380     struct stat s;
 381
 382     if (strchr(name, '/') || !getenv("PATH")) {
 383         return stat(name, &s) == 0 ? xstrdup(name) : NULL;
 384     }
 385
 386     path = xstrdup(getenv("PATH"));
 387     for (dir = strtok_r(path, ":", &save_ptr); dir;
 388          dir = strtok_r(NULL, ":", &save_ptr)) {
 389         char *file = xasprintf("%s/%s", dir, name);
 390         if (stat(file, &s) == 0) {
 391             free(path);
 392             return file;
 393         }
 394         free(file);
 395     }
 396     free(path);
 397     return NULL;
 398 }
 399 \f
 400 /* process_run_capture() and supporting functions. */
 401
 402 struct stream {
 403     size_t max_size;
 404     struct ds log;
 405     int fds[2];
 406 };
 407
 408 static int
 409 stream_open(struct stream *s, size_t max_size)
 410 {
 411     int error;
 412
 413     s->max_size = max_size;
 414     ds_init(&s->log);
 415     if (pipe(s->fds)) {
 416         VLOG_WARN("failed to create pipe: %s", strerror(errno));
 417         return errno;
 418     }
 419     error = set_nonblocking(s->fds[0]);
 420     if (error) {
 421         close(s->fds[0]);
 422         close(s->fds[1]);
 423     }
 424     return error;
 425 }
 426
 427 static void
 428 stream_read(struct stream *s)
 429 {
 430     if (s->fds[0] < 0) {
 431         return;
 432     }
 433
 434     for (;;) {
 435         char buffer[512];
 436         int error;
 437         size_t n;
 438
 439         error = read_fully(s->fds[0], buffer, sizeof buffer, &n);
 440         ds_put_buffer(&s->log, buffer, n);
 441         if (error) {
 442             if (error == EAGAIN || error == EWOULDBLOCK) {
 443                 return;
 444             } else {
 445                 if (error != EOF) {
 446                     VLOG_WARN("error reading subprocess pipe: %s",
 447                               strerror(error));
 448                 }
 449                 break;
 450             }
 451         } else if (s->log.length > s->max_size) {
 452             VLOG_WARN("subprocess output overflowed %zu-byte buffer",
 453                       s->max_size);
 454             break;
 455         }
 456     }
 457     close(s->fds[0]);
 458     s->fds[0] = -1;
 459 }
 460
 461 static void
 462 stream_wait(struct stream *s)
 463 {
 464     if (s->fds[0] >= 0) {
 465         poll_fd_wait(s->fds[0], POLLIN);
 466     }
 467 }
 468
 469 static void
 470 stream_close(struct stream *s)
 471 {
 472     ds_destroy(&s->log);
 473     if (s->fds[0] >= 0) {
 474         close(s->fds[0]);
 475     }
 476     if (s->fds[1] >= 0) {
 477         close(s->fds[1]);
 478     }
 479 }
 480
 481 /* Starts the process whose arguments are given in the null-terminated array
 482  * 'argv' and waits for it to exit.  On success returns 0 and stores the
 483  * process exit value (suitable for passing to process_status_msg()) in
 484  * '*status'.  On failure, returns a positive errno value and stores 0 in
 485  * '*status'.
 486  *
 487  * If 'stdout_log' is nonnull, then the subprocess's output to stdout (up to a
 488  * limit of 'log_max' bytes) is captured in a memory buffer, which
 489  * when this function returns 0 is stored as a null-terminated string in
 490  * '*stdout_log'.  The caller is responsible for freeing '*stdout_log' (by
 491  * passing it to free()).  When this function returns an error, '*stdout_log'
 492  * is set to NULL.
 493  *
 494  * If 'stderr_log' is nonnull, then it is treated like 'stdout_log' except
 495  * that it captures the subprocess's output to stderr. */
 496 int
 497 process_run_capture(char **argv, char **stdout_log, char **stderr_log,
 498                     size_t max_log, int *status)
 499 {
 500     struct stream s_stdout, s_stderr;
 501     sigset_t oldsigs;
 502     pid_t pid;
 503     int error;
 504
 505     COVERAGE_INC(process_run_capture);
 506     if (stdout_log) {
 507         *stdout_log = NULL;
 508     }
 509     if (stderr_log) {
 510         *stderr_log = NULL;
 511     }
 512     *status = 0;
 513     error = process_prestart(argv);
 514     if (error) {
 515         return error;
 516     }
 517
 518     error = stream_open(&s_stdout, max_log);
 519     if (error) {
 520         return error;
 521     }
 522
 523     error = stream_open(&s_stderr, max_log);
 524     if (error) {
 525         stream_close(&s_stdout);
 526         return error;
 527     }
 528
 529     block_sigchld(&oldsigs);
 530     pid = fork();
 531     if (pid < 0) {
 532         error = errno;
 533
 534         unblock_sigchld(&oldsigs);
 535         VLOG_WARN("fork failed: %s", strerror(error));
 536
 537         stream_close(&s_stdout);
 538         stream_close(&s_stderr);
 539         *status = 0;
 540         return error;
 541     } else if (pid) {
 542         /* Running in parent process. */
 543         struct process *p;
 544
 545         p = process_register(argv[0], pid);
 546         unblock_sigchld(&oldsigs);
 547
 548         close(s_stdout.fds[1]);
 549         close(s_stderr.fds[1]);
 550         while (!process_exited(p)) {
 551             stream_read(&s_stdout);
 552             stream_read(&s_stderr);
 553
 554             stream_wait(&s_stdout);
 555             stream_wait(&s_stderr);
 556             process_wait(p);
 557             poll_block();
 558         }
 559         stream_read(&s_stdout);
 560         stream_read(&s_stderr);
 561
 562         if (stdout_log) {
 563             *stdout_log = ds_steal_cstr(&s_stdout.log);
 564         }
 565         if (stderr_log) {
 566             *stderr_log = ds_steal_cstr(&s_stderr.log);
 567         }
 568
 569         stream_close(&s_stdout);
 570         stream_close(&s_stderr);
 571
 572         *status = process_status(p);
 573         process_destroy(p);
 574         return 0;
 575     } else {
 576         /* Running in child process. */
 577         int max_fds;
 578         int i;
 579
 580         fatal_signal_fork();
 581         unblock_sigchld(&oldsigs);
 582
 583         dup2(get_null_fd(), 0);
 584         dup2(s_stdout.fds[1], 1);
 585         dup2(s_stderr.fds[1], 2);
 586
 587         max_fds = get_max_fds();
 588         for (i = 3; i < max_fds; i++) {
 589             close(i);
 590         }
 591
 592         execvp(argv[0], argv);
 593         fprintf(stderr, "execvp(\"%s\") failed: %s\n",
 594                 argv[0], strerror(errno));
 595         exit(EXIT_FAILURE);
 596     }
 597 }
 598 \f
 599 static void
 600 sigchld_handler(int signr OVS_UNUSED)
 601 {
 602     struct process *p;
 603
 604     COVERAGE_INC(process_sigchld);
 605     LIST_FOR_EACH (p, node, &all_processes) {
 606         if (!p->exited) {
 607             int retval, status;
 608             do {
 609                 retval = waitpid(p->pid, &status, WNOHANG);
 610             } while (retval == -1 && errno == EINTR);
 611             if (retval == p->pid) {
 612                 p->exited = true;
 613                 p->status = status;
 614             } else if (retval < 0) {
 615                 /* XXX We want to log something but we're in a signal
 616                  * handler. */
 617                 p->exited = true;
 618                 p->status = -1;
 619             }
 620         }
 621     }
 622     ignore(write(fds[1], "", 1));
 623 }
 624
 625 static bool
 626 is_member(int x, const int *array, size_t n)
 627 {
 628     size_t i;
 629
 630     for (i = 0; i < n; i++) {
 631         if (array[i] == x) {
 632             return true;
 633         }
 634     }
 635     return false;
 636 }
 637
 638 static bool
 639 sigchld_is_blocked(void)
 640 {
 641     sigset_t sigs;
 642
 643     xsigprocmask(SIG_SETMASK, NULL, &sigs);
 644     return sigismember(&sigs, SIGCHLD);
 645 }
 646
 647 static void
 648 block_sigchld(sigset_t *oldsigs)
 649 {
 650     sigset_t sigchld;
 651
 652     sigemptyset(&sigchld);
 653     sigaddset(&sigchld, SIGCHLD);
 654     xsigprocmask(SIG_BLOCK, &sigchld, oldsigs);
 655 }
 656
 657 static void
 658 unblock_sigchld(const sigset_t *oldsigs)
 659 {
 660     xsigprocmask(SIG_SETMASK, oldsigs, NULL);
 661 }