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/resource.h>
  25 #include <sys/stat.h>
  26 #include <sys/wait.h>
  27 #include <unistd.h>
  28 #include "coverage.h"
  29 #include "openvswitch/dynamic-string.h"
  30 #include "fatal-signal.h"
  31 #include "openvswitch/list.h"
  32 #include "ovs-thread.h"
  33 #include "poll-loop.h"
  34 #include "signals.h"
  35 #include "socket-util.h"
  36 #include "util.h"
  37 #include "openvswitch/vlog.h"
  38
  39 VLOG_DEFINE_THIS_MODULE(process);
  40
  41 COVERAGE_DEFINE(process_start);
  42
  43 struct process {
  44     struct ovs_list node;
  45     char *name;
  46     pid_t pid;
  47
  48     /* State. */
  49     bool exited;
  50     int status;
  51 };
  52
  53 /* Pipe used to signal child termination. */
  54 static int fds[2];
  55
  56 /* All processes. */
  57 static struct ovs_list all_processes = OVS_LIST_INITIALIZER(&all_processes);
  58
  59 static void sigchld_handler(int signr OVS_UNUSED);
  60
  61 /* Initializes the process subsystem (if it is not already initialized).  Calls
  62  * exit() if initialization fails.
  63  *
  64  * This function may not be called after creating any additional threads.
  65  *
  66  * Calling this function is optional; it will be called automatically by
  67  * process_start() if necessary.  Calling it explicitly allows the client to
  68  * prevent the process from exiting at an unexpected time. */
  69 void
  70 process_init(void)
  71 {
  72 #ifndef _WIN32
  73     static bool inited;
  74     struct sigaction sa;
  75
  76     assert_single_threaded();
  77     if (inited) {
  78         return;
  79     }
  80     inited = true;
  81
  82     /* Create notification pipe. */
  83     xpipe_nonblocking(fds);
  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     xsigaction(SIGCHLD, &sa, NULL);
  91 #endif
  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 static struct process *
 153 process_register(const char *name, pid_t pid)
 154 {
 155     struct process *p;
 156     const char *slash;
 157
 158     p = xzalloc(sizeof *p);
 159     p->pid = pid;
 160     slash = strrchr(name, '/');
 161     p->name = xstrdup(slash ? slash + 1 : name);
 162     p->exited = false;
 163
 164     ovs_list_push_back(&all_processes, &p->node);
 165
 166     return p;
 167 }
 168
 169 #ifndef _WIN32
 170 static bool
 171 rlim_is_finite(rlim_t limit)
 172 {
 173     if (limit == RLIM_INFINITY) {
 174         return false;
 175     }
 176
 177 #ifdef RLIM_SAVED_CUR           /* FreeBSD 8.0 lacks RLIM_SAVED_CUR. */
 178     if (limit == RLIM_SAVED_CUR) {
 179         return false;
 180     }
 181 #endif
 182
 183 #ifdef RLIM_SAVED_MAX           /* FreeBSD 8.0 lacks RLIM_SAVED_MAX. */
 184     if (limit == RLIM_SAVED_MAX) {
 185         return false;
 186     }
 187 #endif
 188
 189     return true;
 190 }
 191
 192 /* Returns the maximum valid FD value, plus 1. */
 193 static int
 194 get_max_fds(void)
 195 {
 196     static int max_fds;
 197
 198     if (!max_fds) {
 199         struct rlimit r;
 200         if (!getrlimit(RLIMIT_NOFILE, &r) && rlim_is_finite(r.rlim_cur)) {
 201             max_fds = r.rlim_cur;
 202         } else {
 203             VLOG_WARN("failed to obtain fd limit, defaulting to 1024");
 204             max_fds = 1024;
 205         }
 206     }
 207
 208     return max_fds;
 209 }
 210 #endif /* _WIN32 */
 211
 212 /* Starts a subprocess with the arguments in the null-terminated argv[] array.
 213  * argv[0] is used as the name of the process.  Searches the PATH environment
 214  * variable to find the program to execute.
 215  *
 216  * This function may not be called after creating any additional threads.
 217  *
 218  * All file descriptors are closed before executing the subprocess, except for
 219  * fds 0, 1, and 2.
 220  *
 221  * Returns 0 if successful, otherwise a positive errno value indicating the
 222  * error.  If successful, '*pp' is assigned a new struct process that may be
 223  * used to query the process's status.  On failure, '*pp' is set to NULL. */
 224 int
 225 process_start(char **argv, struct process **pp)
 226 {
 227 #ifndef _WIN32
 228     pid_t pid;
 229     int error;
 230     sigset_t prev_mask;
 231
 232     assert_single_threaded();
 233
 234     *pp = NULL;
 235     COVERAGE_INC(process_start);
 236     error = process_prestart(argv);
 237     if (error) {
 238         return error;
 239     }
 240
 241     fatal_signal_block(&prev_mask);
 242     pid = fork();
 243     if (pid < 0) {
 244         VLOG_WARN("fork failed: %s", ovs_strerror(errno));
 245         error = errno;
 246     } else if (pid) {
 247         /* Running in parent process. */
 248         *pp = process_register(argv[0], pid);
 249         error = 0;
 250     } else {
 251         /* Running in child process. */
 252         int fd_max = get_max_fds();
 253         int fd;
 254
 255         fatal_signal_fork();
 256         for (fd = 3; fd < fd_max; fd++) {
 257             close(fd);
 258         }
 259         xpthread_sigmask(SIG_SETMASK, &prev_mask, NULL);
 260         execvp(argv[0], argv);
 261         fprintf(stderr, "execvp(\"%s\") failed: %s\n",
 262                 argv[0], ovs_strerror(errno));
 263         _exit(1);
 264     }
 265     xpthread_sigmask(SIG_SETMASK, &prev_mask, NULL);
 266     return error;
 267 #else
 268     *pp = NULL;
 269     return ENOSYS;
 270 #endif
 271 }
 272
 273 /* Destroys process 'p'. */
 274 void
 275 process_destroy(struct process *p)
 276 {
 277     if (p) {
 278         ovs_list_remove(&p->node);
 279         free(p->name);
 280         free(p);
 281     }
 282 }
 283
 284 /* Sends signal 'signr' to process 'p'.  Returns 0 if successful, otherwise a
 285  * positive errno value. */
 286 int
 287 process_kill(const struct process *p, int signr)
 288 {
 289 #ifndef _WIN32
 290     return (p->exited ? ESRCH
 291             : !kill(p->pid, signr) ? 0
 292             : errno);
 293 #else
 294     return ENOSYS;
 295 #endif
 296 }
 297
 298 /* Returns the pid of process 'p'. */
 299 pid_t
 300 process_pid(const struct process *p)
 301 {
 302     return p->pid;
 303 }
 304
 305 /* Returns the name of process 'p' (the name passed to process_start() with any
 306  * leading directories stripped). */
 307 const char *
 308 process_name(const struct process *p)
 309 {
 310     return p->name;
 311 }
 312
 313 /* Returns true if process 'p' has exited, false otherwise. */
 314 bool
 315 process_exited(struct process *p)
 316 {
 317     return p->exited;
 318 }
 319
 320 /* Returns process 'p''s exit status, as reported by waitpid(2).
 321  * process_status(p) may be called only after process_exited(p) has returned
 322  * true. */
 323 int
 324 process_status(const struct process *p)
 325 {
 326     ovs_assert(p->exited);
 327     return p->status;
 328 }
 329
 330 /* Given 'status', which is a process status in the form reported by waitpid(2)
 331  * and returned by process_status(), returns a string describing how the
 332  * process terminated.  The caller is responsible for freeing the string when
 333  * it is no longer needed. */
 334 char *
 335 process_status_msg(int status)
 336 {
 337     struct ds ds = DS_EMPTY_INITIALIZER;
 338 #ifndef _WIN32
 339     if (WIFEXITED(status)) {
 340         ds_put_format(&ds, "exit status %d", WEXITSTATUS(status));
 341     } else if (WIFSIGNALED(status)) {
 342         char namebuf[SIGNAL_NAME_BUFSIZE];
 343
 344         ds_put_format(&ds, "killed (%s)",
 345                       signal_name(WTERMSIG(status), namebuf, sizeof namebuf));
 346     } else if (WIFSTOPPED(status)) {
 347         char namebuf[SIGNAL_NAME_BUFSIZE];
 348
 349         ds_put_format(&ds, "stopped (%s)",
 350                       signal_name(WSTOPSIG(status), namebuf, sizeof namebuf));
 351     } else {
 352         ds_put_format(&ds, "terminated abnormally (%x)", status);
 353     }
 354     if (WCOREDUMP(status)) {
 355         ds_put_cstr(&ds, ", core dumped");
 356     }
 357 #else
 358     ds_put_cstr(&ds, "function not supported.");
 359 #endif
 360     return ds_cstr(&ds);
 361 }
 362
 363 /* Executes periodic maintenance activities required by the process module. */
 364 void
 365 process_run(void)
 366 {
 367 #ifndef _WIN32
 368     char buf[_POSIX_PIPE_BUF];
 369
 370     if (!ovs_list_is_empty(&all_processes) && read(fds[0], buf, sizeof buf) > 0) {
 371         struct process *p;
 372
 373         LIST_FOR_EACH (p, node, &all_processes) {
 374             if (!p->exited) {
 375                 int retval, status;
 376                 do {
 377                     retval = waitpid(p->pid, &status, WNOHANG);
 378                 } while (retval == -1 && errno == EINTR);
 379                 if (retval == p->pid) {
 380                     p->exited = true;
 381                     p->status = status;
 382                 } else if (retval < 0) {
 383                     VLOG_WARN("waitpid: %s", ovs_strerror(errno));
 384                     p->exited = true;
 385                     p->status = -1;
 386                 }
 387             }
 388         }
 389     }
 390 #endif
 391 }
 392
 393
 394 /* Causes the next call to poll_block() to wake up when process 'p' has
 395  * exited. */
 396 void
 397 process_wait(struct process *p)
 398 {
 399 #ifndef _WIN32
 400     if (p->exited) {
 401         poll_immediate_wake();
 402     } else {
 403         poll_fd_wait(fds[0], POLLIN);
 404     }
 405 #else
 406     OVS_NOT_REACHED();
 407 #endif
 408 }
 409
 410 char *
 411 process_search_path(const char *name)
 412 {
 413     char *save_ptr = NULL;
 414     char *path, *dir;
 415     struct stat s;
 416
 417     if (strchr(name, '/') || !getenv("PATH")) {
 418         return stat(name, &s) == 0 ? xstrdup(name) : NULL;
 419     }
 420
 421     path = xstrdup(getenv("PATH"));
 422     for (dir = strtok_r(path, ":", &save_ptr); dir;
 423          dir = strtok_r(NULL, ":", &save_ptr)) {
 424         char *file = xasprintf("%s/%s", dir, name);
 425         if (stat(file, &s) == 0) {
 426             free(path);
 427             return file;
 428         }
 429         free(file);
 430     }
 431     free(path);
 432     return NULL;
 433 }
 434 \f
 435 static void
 436 sigchld_handler(int signr OVS_UNUSED)
 437 {
 438     ignore(write(fds[1], "", 1));
 439 }