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 "ovs-thread.h"
  32 #include "poll-loop.h"
  33 #include "signals.h"
  34 #include "socket-util.h"
  35 #include "util.h"
  36 #include "vlog.h"
  37
  38 VLOG_DEFINE_THIS_MODULE(process);
  39
  40 COVERAGE_DEFINE(process_start);
  41
  42 struct process {
  43     struct list node;
  44     char *name;
  45     pid_t pid;
  46
  47     /* State. */
  48     bool exited;
  49     int status;
  50 };
  51
  52 /* Pipe used to signal child termination. */
  53 static int fds[2];
  54
  55 /* All processes. */
  56 static struct list all_processes = LIST_INITIALIZER(&all_processes);
  57
  58 static void sigchld_handler(int signr OVS_UNUSED);
  59
  60 /* Initializes the process subsystem (if it is not already initialized).  Calls
  61  * exit() if initialization fails.
  62  *
  63  * This function may not be called after creating any additional threads.
  64  *
  65  * Calling this function is optional; it will be called automatically by
  66  * process_start() if necessary.  Calling it explicitly allows the client to
  67  * prevent the process from exiting at an unexpected time. */
  68 void
  69 process_init(void)
  70 {
  71 #ifndef _WIN32
  72     static bool inited;
  73     struct sigaction sa;
  74
  75     assert_single_threaded();
  76     if (inited) {
  77         return;
  78     }
  79     inited = true;
  80
  81     /* Create notification pipe. */
  82     xpipe_nonblocking(fds);
  83
  84     /* Set up child termination signal handler. */
  85     memset(&sa, 0, sizeof sa);
  86     sa.sa_handler = sigchld_handler;
  87     sigemptyset(&sa.sa_mask);
  88     sa.sa_flags = SA_NOCLDSTOP | SA_RESTART;
  89     xsigaction(SIGCHLD, &sa, NULL);
  90 #endif
  91 }
  92
  93 char *
  94 process_escape_args(char **argv)
  95 {
  96     struct ds ds = DS_EMPTY_INITIALIZER;
  97     char **argp;
  98     for (argp = argv; *argp; argp++) {
  99         const char *arg = *argp;
 100         const char *p;
 101         if (argp != argv) {
 102             ds_put_char(&ds, ' ');
 103         }
 104         if (arg[strcspn(arg, " \t\r\n\v\\\'\"")]) {
 105             ds_put_char(&ds, '"');
 106             for (p = arg; *p; p++) {
 107                 if (*p == '\\' || *p == '\"') {
 108                     ds_put_char(&ds, '\\');
 109                 }
 110                 ds_put_char(&ds, *p);
 111             }
 112             ds_put_char(&ds, '"');
 113         } else {
 114             ds_put_cstr(&ds, arg);
 115         }
 116     }
 117     return ds_cstr(&ds);
 118 }
 119
 120 /* Prepare to start a process whose command-line arguments are given by the
 121  * null-terminated 'argv' array.  Returns 0 if successful, otherwise a
 122  * positive errno value. */
 123 static int
 124 process_prestart(char **argv)
 125 {
 126     char *binary;
 127
 128     process_init();
 129
 130     /* Log the process to be started. */
 131     if (VLOG_IS_DBG_ENABLED()) {
 132         char *args = process_escape_args(argv);
 133         VLOG_DBG("starting subprocess: %s", args);
 134         free(args);
 135     }
 136
 137     /* execvp() will search PATH too, but the error in that case is more
 138      * obscure, since it is only reported post-fork. */
 139     binary = process_search_path(argv[0]);
 140     if (!binary) {
 141         VLOG_ERR("%s not found in PATH", argv[0]);
 142         return ENOENT;
 143     }
 144     free(binary);
 145
 146     return 0;
 147 }
 148
 149 /* Creates and returns a new struct process with the specified 'name' and
 150  * 'pid'. */
 151 static struct process *
 152 process_register(const char *name, pid_t pid)
 153 {
 154     struct process *p;
 155     const char *slash;
 156
 157     p = xzalloc(sizeof *p);
 158     p->pid = pid;
 159     slash = strrchr(name, '/');
 160     p->name = xstrdup(slash ? slash + 1 : name);
 161     p->exited = false;
 162
 163     list_push_back(&all_processes, &p->node);
 164
 165     return p;
 166 }
 167
 168 /* Starts a subprocess with the arguments in the null-terminated argv[] array.
 169  * argv[0] is used as the name of the process.  Searches the PATH environment
 170  * variable to find the program to execute.
 171  *
 172  * This function may not be called after creating any additional threads.
 173  *
 174  * All file descriptors are closed before executing the subprocess, except for
 175  * fds 0, 1, and 2.
 176  *
 177  * Returns 0 if successful, otherwise a positive errno value indicating the
 178  * error.  If successful, '*pp' is assigned a new struct process that may be
 179  * used to query the process's status.  On failure, '*pp' is set to NULL. */
 180 int
 181 process_start(char **argv, struct process **pp)
 182 {
 183 #ifndef _WIN32
 184     pid_t pid;
 185     int error;
 186
 187     assert_single_threaded();
 188
 189     *pp = NULL;
 190     COVERAGE_INC(process_start);
 191     error = process_prestart(argv);
 192     if (error) {
 193         return error;
 194     }
 195
 196     pid = fork();
 197     if (pid < 0) {
 198         VLOG_WARN("fork failed: %s", ovs_strerror(errno));
 199         return errno;
 200     } else if (pid) {
 201         /* Running in parent process. */
 202         *pp = process_register(argv[0], pid);
 203         return 0;
 204     } else {
 205         /* Running in child process. */
 206         int fd_max = get_max_fds();
 207         int fd;
 208
 209         fatal_signal_fork();
 210         for (fd = 3; fd < fd_max; fd++) {
 211             close(fd);
 212         }
 213         execvp(argv[0], argv);
 214         fprintf(stderr, "execvp(\"%s\") failed: %s\n",
 215                 argv[0], ovs_strerror(errno));
 216         _exit(1);
 217     }
 218 #else
 219     *pp = NULL;
 220     return ENOSYS;
 221 #endif
 222 }
 223
 224 /* Destroys process 'p'. */
 225 void
 226 process_destroy(struct process *p)
 227 {
 228     if (p) {
 229         list_remove(&p->node);
 230         free(p->name);
 231         free(p);
 232     }
 233 }
 234
 235 /* Sends signal 'signr' to process 'p'.  Returns 0 if successful, otherwise a
 236  * positive errno value. */
 237 int
 238 process_kill(const struct process *p, int signr)
 239 {
 240 #ifndef _WIN32
 241     return (p->exited ? ESRCH
 242             : !kill(p->pid, signr) ? 0
 243             : errno);
 244 #else
 245     return ENOSYS;
 246 #endif
 247 }
 248
 249 /* Returns the pid of process 'p'. */
 250 pid_t
 251 process_pid(const struct process *p)
 252 {
 253     return p->pid;
 254 }
 255
 256 /* Returns the name of process 'p' (the name passed to process_start() with any
 257  * leading directories stripped). */
 258 const char *
 259 process_name(const struct process *p)
 260 {
 261     return p->name;
 262 }
 263
 264 /* Returns true if process 'p' has exited, false otherwise. */
 265 bool
 266 process_exited(struct process *p)
 267 {
 268     return p->exited;
 269 }
 270
 271 /* Returns process 'p''s exit status, as reported by waitpid(2).
 272  * process_status(p) may be called only after process_exited(p) has returned
 273  * true. */
 274 int
 275 process_status(const struct process *p)
 276 {
 277     ovs_assert(p->exited);
 278     return p->status;
 279 }
 280
 281 /* Given 'status', which is a process status in the form reported by waitpid(2)
 282  * and returned by process_status(), returns a string describing how the
 283  * process terminated.  The caller is responsible for freeing the string when
 284  * it is no longer needed. */
 285 char *
 286 process_status_msg(int status)
 287 {
 288     struct ds ds = DS_EMPTY_INITIALIZER;
 289 #ifndef _WIN32
 290     if (WIFEXITED(status)) {
 291         ds_put_format(&ds, "exit status %d", WEXITSTATUS(status));
 292     } else if (WIFSIGNALED(status)) {
 293         char namebuf[SIGNAL_NAME_BUFSIZE];
 294
 295         ds_put_format(&ds, "killed (%s)",
 296                       signal_name(WTERMSIG(status), namebuf, sizeof namebuf));
 297     } else if (WIFSTOPPED(status)) {
 298         char namebuf[SIGNAL_NAME_BUFSIZE];
 299
 300         ds_put_format(&ds, "stopped (%s)",
 301                       signal_name(WSTOPSIG(status), namebuf, sizeof namebuf));
 302     } else {
 303         ds_put_format(&ds, "terminated abnormally (%x)", status);
 304     }
 305     if (WCOREDUMP(status)) {
 306         ds_put_cstr(&ds, ", core dumped");
 307     }
 308 #else
 309     ds_put_cstr(&ds, "function not supported.");
 310 #endif
 311     return ds_cstr(&ds);
 312 }
 313
 314 /* Executes periodic maintenance activities required by the process module. */
 315 void
 316 process_run(void)
 317 {
 318 #ifndef _WIN32
 319     char buf[_POSIX_PIPE_BUF];
 320
 321     if (!list_is_empty(&all_processes) && read(fds[0], buf, sizeof buf) > 0) {
 322         struct process *p;
 323
 324         LIST_FOR_EACH (p, node, &all_processes) {
 325             if (!p->exited) {
 326                 int retval, status;
 327                 do {
 328                     retval = waitpid(p->pid, &status, WNOHANG);
 329                 } while (retval == -1 && errno == EINTR);
 330                 if (retval == p->pid) {
 331                     p->exited = true;
 332                     p->status = status;
 333                 } else if (retval < 0) {
 334                     VLOG_WARN("waitpid: %s", ovs_strerror(errno));
 335                     p->exited = true;
 336                     p->status = -1;
 337                 }
 338             }
 339         }
 340     }
 341 #endif
 342 }
 343
 344
 345 /* Causes the next call to poll_block() to wake up when process 'p' has
 346  * exited. */
 347 void
 348 process_wait(struct process *p)
 349 {
 350 #ifndef _WIN32
 351     if (p->exited) {
 352         poll_immediate_wake();
 353     } else {
 354         poll_fd_wait(fds[0], POLLIN);
 355     }
 356 #else
 357     OVS_NOT_REACHED();
 358 #endif
 359 }
 360
 361 char *
 362 process_search_path(const char *name)
 363 {
 364     char *save_ptr = NULL;
 365     char *path, *dir;
 366     struct stat s;
 367
 368     if (strchr(name, '/') || !getenv("PATH")) {
 369         return stat(name, &s) == 0 ? xstrdup(name) : NULL;
 370     }
 371
 372     path = xstrdup(getenv("PATH"));
 373     for (dir = strtok_r(path, ":", &save_ptr); dir;
 374          dir = strtok_r(NULL, ":", &save_ptr)) {
 375         char *file = xasprintf("%s/%s", dir, name);
 376         if (stat(file, &s) == 0) {
 377             free(path);
 378             return file;
 379         }
 380         free(file);
 381     }
 382     free(path);
 383     return NULL;
 384 }
 385 \f
 386 static void
 387 sigchld_handler(int signr OVS_UNUSED)
 388 {
 389     ignore(write(fds[1], "", 1));
 390 }