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     /* Modified by signal handler. */
  48     volatile bool exited;
  49     volatile 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 bool sigchld_is_blocked(void);
  59 static void block_sigchld(sigset_t *);
  60 static void unblock_sigchld(const sigset_t *);
  61 static void sigchld_handler(int signr OVS_UNUSED);
  62
  63 /* Initializes the process subsystem (if it is not already initialized).  Calls
  64  * exit() if initialization fails.
  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     static bool inited;
  73     struct sigaction sa;
  74
  75     if (inited) {
  76         return;
  77     }
  78     inited = true;
  79
  80     /* Create notification pipe. */
  81     xpipe_nonblocking(fds);
  82
  83     /* Set up child termination signal handler. */
  84     memset(&sa, 0, sizeof sa);
  85     sa.sa_handler = sigchld_handler;
  86     sigemptyset(&sa.sa_mask);
  87     sa.sa_flags = SA_NOCLDSTOP | SA_RESTART;
  88     xsigaction(SIGCHLD, &sa, NULL);
  89 }
  90
  91 char *
  92 process_escape_args(char **argv)
  93 {
  94     struct ds ds = DS_EMPTY_INITIALIZER;
  95     char **argp;
  96     for (argp = argv; *argp; argp++) {
  97         const char *arg = *argp;
  98         const char *p;
  99         if (argp != argv) {
 100             ds_put_char(&ds, ' ');
 101         }
 102         if (arg[strcspn(arg, " \t\r\n\v\\\'\"")]) {
 103             ds_put_char(&ds, '"');
 104             for (p = arg; *p; p++) {
 105                 if (*p == '\\' || *p == '\"') {
 106                     ds_put_char(&ds, '\\');
 107                 }
 108                 ds_put_char(&ds, *p);
 109             }
 110             ds_put_char(&ds, '"');
 111         } else {
 112             ds_put_cstr(&ds, arg);
 113         }
 114     }
 115     return ds_cstr(&ds);
 116 }
 117
 118 /* Prepare to start a process whose command-line arguments are given by the
 119  * null-terminated 'argv' array.  Returns 0 if successful, otherwise a
 120  * positive errno value. */
 121 static int
 122 process_prestart(char **argv)
 123 {
 124     char *binary;
 125
 126     process_init();
 127
 128     /* Log the process to be started. */
 129     if (VLOG_IS_DBG_ENABLED()) {
 130         char *args = process_escape_args(argv);
 131         VLOG_DBG("starting subprocess: %s", args);
 132         free(args);
 133     }
 134
 135     /* execvp() will search PATH too, but the error in that case is more
 136      * obscure, since it is only reported post-fork. */
 137     binary = process_search_path(argv[0]);
 138     if (!binary) {
 139         VLOG_ERR("%s not found in PATH", argv[0]);
 140         return ENOENT;
 141     }
 142     free(binary);
 143
 144     return 0;
 145 }
 146
 147 /* Creates and returns a new struct process with the specified 'name' and
 148  * 'pid'.
 149  *
 150  * This is racy unless SIGCHLD is blocked (and has been blocked since before
 151  * the fork()) that created the subprocess.  */
 152 static struct process *
 153 process_register(const char *name, pid_t pid)
 154 {
 155     struct process *p;
 156     const char *slash;
 157
 158     ovs_assert(sigchld_is_blocked());
 159
 160     p = xzalloc(sizeof *p);
 161     p->pid = pid;
 162     slash = strrchr(name, '/');
 163     p->name = xstrdup(slash ? slash + 1 : name);
 164     p->exited = false;
 165
 166     list_push_back(&all_processes, &p->node);
 167
 168     return p;
 169 }
 170
 171 /* Starts a subprocess with the arguments in the null-terminated argv[] array.
 172  * argv[0] is used as the name of the process.  Searches the PATH environment
 173  * variable to find the program to execute.
 174  *
 175  * All file descriptors are closed before executing the subprocess, except for
 176  * fds 0, 1, and 2.
 177  *
 178  * Returns 0 if successful, otherwise a positive errno value indicating the
 179  * error.  If successful, '*pp' is assigned a new struct process that may be
 180  * used to query the process's status.  On failure, '*pp' is set to NULL. */
 181 int
 182 process_start(char **argv, struct process **pp)
 183 {
 184     sigset_t oldsigs;
 185     pid_t pid;
 186     int error;
 187
 188     *pp = NULL;
 189     COVERAGE_INC(process_start);
 190     error = process_prestart(argv);
 191     if (error) {
 192         return error;
 193     }
 194
 195     block_sigchld(&oldsigs);
 196     pid = fork();
 197     if (pid < 0) {
 198         unblock_sigchld(&oldsigs);
 199         VLOG_WARN("fork failed: %s", strerror(errno));
 200         return errno;
 201     } else if (pid) {
 202         /* Running in parent process. */
 203         *pp = process_register(argv[0], pid);
 204         unblock_sigchld(&oldsigs);
 205         return 0;
 206     } else {
 207         /* Running in child process. */
 208         int fd_max = get_max_fds();
 209         int fd;
 210
 211         fatal_signal_fork();
 212         unblock_sigchld(&oldsigs);
 213         for (fd = 3; fd < fd_max; fd++) {
 214             close(fd);
 215         }
 216         execvp(argv[0], argv);
 217         fprintf(stderr, "execvp(\"%s\") failed: %s\n",
 218                 argv[0], strerror(errno));
 219         _exit(1);
 220     }
 221 }
 222
 223 /* Destroys process 'p'. */
 224 void
 225 process_destroy(struct process *p)
 226 {
 227     if (p) {
 228         sigset_t oldsigs;
 229
 230         block_sigchld(&oldsigs);
 231         list_remove(&p->node);
 232         unblock_sigchld(&oldsigs);
 233
 234         free(p->name);
 235         free(p);
 236     }
 237 }
 238
 239 /* Sends signal 'signr' to process 'p'.  Returns 0 if successful, otherwise a
 240  * positive errno value. */
 241 int
 242 process_kill(const struct process *p, int signr)
 243 {
 244     return (p->exited ? ESRCH
 245             : !kill(p->pid, signr) ? 0
 246             : errno);
 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     if (p->exited) {
 269         return true;
 270     } else {
 271         char buf[_POSIX_PIPE_BUF];
 272         ignore(read(fds[0], buf, sizeof buf));
 273         return false;
 274     }
 275 }
 276
 277 /* Returns process 'p''s exit status, as reported by waitpid(2).
 278  * process_status(p) may be called only after process_exited(p) has returned
 279  * true. */
 280 int
 281 process_status(const struct process *p)
 282 {
 283     ovs_assert(p->exited);
 284     return p->status;
 285 }
 286
 287 /* Given 'status', which is a process status in the form reported by waitpid(2)
 288  * and returned by process_status(), returns a string describing how the
 289  * process terminated.  The caller is responsible for freeing the string when
 290  * it is no longer needed. */
 291 char *
 292 process_status_msg(int status)
 293 {
 294     struct ds ds = DS_EMPTY_INITIALIZER;
 295     if (WIFEXITED(status)) {
 296         ds_put_format(&ds, "exit status %d", WEXITSTATUS(status));
 297     } else if (WIFSIGNALED(status)) {
 298         char namebuf[SIGNAL_NAME_BUFSIZE];
 299
 300         ds_put_format(&ds, "killed (%s)",
 301                       signal_name(WTERMSIG(status), namebuf, sizeof namebuf));
 302     } else if (WIFSTOPPED(status)) {
 303         char namebuf[SIGNAL_NAME_BUFSIZE];
 304
 305         ds_put_format(&ds, "stopped (%s)",
 306                       signal_name(WSTOPSIG(status), namebuf, sizeof namebuf));
 307     } else {
 308         ds_put_format(&ds, "terminated abnormally (%x)", status);
 309     }
 310     if (WCOREDUMP(status)) {
 311         ds_put_cstr(&ds, ", core dumped");
 312     }
 313     return ds_cstr(&ds);
 314 }
 315
 316 /* Causes the next call to poll_block() to wake up when process 'p' has
 317  * exited. */
 318 void
 319 process_wait(struct process *p)
 320 {
 321     if (p->exited) {
 322         poll_immediate_wake();
 323     } else {
 324         poll_fd_wait(fds[0], POLLIN);
 325     }
 326 }
 327
 328 char *
 329 process_search_path(const char *name)
 330 {
 331     char *save_ptr = NULL;
 332     char *path, *dir;
 333     struct stat s;
 334
 335     if (strchr(name, '/') || !getenv("PATH")) {
 336         return stat(name, &s) == 0 ? xstrdup(name) : NULL;
 337     }
 338
 339     path = xstrdup(getenv("PATH"));
 340     for (dir = strtok_r(path, ":", &save_ptr); dir;
 341          dir = strtok_r(NULL, ":", &save_ptr)) {
 342         char *file = xasprintf("%s/%s", dir, name);
 343         if (stat(file, &s) == 0) {
 344             free(path);
 345             return file;
 346         }
 347         free(file);
 348     }
 349     free(path);
 350     return NULL;
 351 }
 352 \f
 353 static void
 354 sigchld_handler(int signr OVS_UNUSED)
 355 {
 356     struct process *p;
 357
 358     COVERAGE_INC(process_sigchld);
 359     LIST_FOR_EACH (p, node, &all_processes) {
 360         if (!p->exited) {
 361             int retval, status;
 362             do {
 363                 retval = waitpid(p->pid, &status, WNOHANG);
 364             } while (retval == -1 && errno == EINTR);
 365             if (retval == p->pid) {
 366                 p->exited = true;
 367                 p->status = status;
 368             } else if (retval < 0) {
 369                 /* XXX We want to log something but we're in a signal
 370                  * handler. */
 371                 p->exited = true;
 372                 p->status = -1;
 373             }
 374         }
 375     }
 376     ignore(write(fds[1], "", 1));
 377 }
 378
 379 static bool
 380 sigchld_is_blocked(void)
 381 {
 382     sigset_t sigs;
 383
 384     xpthread_sigmask(SIG_SETMASK, NULL, &sigs);
 385     return sigismember(&sigs, SIGCHLD);
 386 }
 387
 388 static void
 389 block_sigchld(sigset_t *oldsigs)
 390 {
 391     sigset_t sigchld;
 392
 393     sigemptyset(&sigchld);
 394     sigaddset(&sigchld, SIGCHLD);
 395     xpthread_sigmask(SIG_BLOCK, &sigchld, oldsigs);
 396 }
 397
 398 static void
 399 unblock_sigchld(const sigset_t *oldsigs)
 400 {
 401     xpthread_sigmask(SIG_SETMASK, oldsigs, NULL);
 402 }