lib/process.c

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