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