gdb/common/filestuff.c

   1 /* Low-level file-handling.
   2    Copyright (C) 2012-2017 Free Software Foundation, Inc.
   3
   4    This file is part of GDB.
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  18
  19 #include "common-defs.h"
  20 #include "filestuff.h"
  21 #include "gdb_vecs.h"
  22 #include <fcntl.h>
  23 #include <unistd.h>
  24 #include <sys/types.h>
  25 #include <sys/stat.h>
  26
  27 #ifdef USE_WIN32API
  28 #include <winsock2.h>
  29 #include <windows.h>
  30 #define HAVE_SOCKETS 1
  31 #elif defined HAVE_SYS_SOCKET_H
  32 #include <sys/socket.h>
  33 /* Define HAVE_F_GETFD if we plan to use F_GETFD.  */
  34 #define HAVE_F_GETFD F_GETFD
  35 #define HAVE_SOCKETS 1
  36 #endif
  37
  38 #ifdef HAVE_SYS_RESOURCE_H
  39 #include <sys/resource.h>
  40 #endif /* HAVE_SYS_RESOURCE_H */
  41
  42 #ifndef O_CLOEXEC
  43 #define O_CLOEXEC 0
  44 #endif
  45
  46 #ifndef SOCK_CLOEXEC
  47 #define SOCK_CLOEXEC 0
  48 #endif
  49
  50 \f
  51
  52 #ifndef HAVE_FDWALK
  53
  54 #include <dirent.h>
  55
  56 /* Replacement for fdwalk, if the system doesn't define it.  Walks all
  57    open file descriptors (though this implementation may walk closed
  58    ones as well, depending on the host platform's capabilities) and
  59    call FUNC with ARG.  If FUNC returns non-zero, stops immediately
  60    and returns the same value.  Otherwise, returns zero when
  61    finished.  */
  62
  63 static int
  64 fdwalk (int (*func) (void *, int), void *arg)
  65 {
  66   /* Checking __linux__ isn't great but it isn't clear what would be
  67      better.  There doesn't seem to be a good way to check for this in
  68      configure.  */
  69 #ifdef __linux__
  70   DIR *dir;
  71
  72   dir = opendir ("/proc/self/fd");
  73   if (dir != NULL)
  74     {
  75       struct dirent *entry;
  76       int result = 0;
  77
  78       for (entry = readdir (dir); entry != NULL; entry = readdir (dir))
  79         {
  80           long fd;
  81           char *tail;
  82           int result;
  83
  84           errno = 0;
  85           fd = strtol (entry->d_name, &tail, 10);
  86           if (*tail != '\0' || errno != 0)
  87             continue;
  88           if ((int) fd != fd)
  89             {
  90               /* What can we do here really?  */
  91               continue;
  92             }
  93
  94           if (fd == dirfd (dir))
  95             continue;
  96
  97           result = func (arg, fd);
  98           if (result != 0)
  99             break;
 100         }
 101
 102       closedir (dir);
 103       return result;
 104     }
 105   /* We may fall through to the next case.  */
 106 #endif
 107
 108   {
 109     int max, fd;
 110
 111 #if defined(HAVE_GETRLIMIT) && defined(RLIMIT_NOFILE)
 112     struct rlimit rlim;
 113
 114     if (getrlimit (RLIMIT_NOFILE, &rlim) == 0 && rlim.rlim_max != RLIM_INFINITY)
 115       max = rlim.rlim_max;
 116     else
 117 #endif
 118       {
 119 #ifdef _SC_OPEN_MAX
 120         max = sysconf (_SC_OPEN_MAX);
 121 #else
 122         /* Whoops.  */
 123         return 0;
 124 #endif /* _SC_OPEN_MAX */
 125       }
 126
 127     for (fd = 0; fd < max; ++fd)
 128       {
 129         struct stat sb;
 130         int result;
 131
 132         /* Only call FUNC for open fds.  */
 133         if (fstat (fd, &sb) == -1)
 134           continue;
 135
 136         result = func (arg, fd);
 137         if (result != 0)
 138           return result;
 139       }
 140
 141     return 0;
 142   }
 143 }
 144
 145 #endif /* HAVE_FDWALK */
 146
 147 \f
 148
 149 /* A VEC holding all the fds open when notice_open_fds was called.  We
 150    don't use a hashtab because libiberty isn't linked into gdbserver;
 151    and anyway we don't expect there to be many open fds.  */
 152
 153 static VEC (int) *open_fds;
 154
 155 /* An fdwalk callback function used by notice_open_fds.  It puts the
 156    given file descriptor into the vec.  */
 157
 158 static int
 159 do_mark_open_fd (void *ignore, int fd)
 160 {
 161   VEC_safe_push (int, open_fds, fd);
 162   return 0;
 163 }
 164
 165 /* See filestuff.h.  */
 166
 167 void
 168 notice_open_fds (void)
 169 {
 170   fdwalk (do_mark_open_fd, NULL);
 171 }
 172
 173 /* See filestuff.h.  */
 174
 175 void
 176 mark_fd_no_cloexec (int fd)
 177 {
 178   do_mark_open_fd (NULL, fd);
 179 }
 180
 181 /* See filestuff.h.  */
 182
 183 void
 184 unmark_fd_no_cloexec (int fd)
 185 {
 186   int i, val;
 187
 188   for (i = 0; VEC_iterate (int, open_fds, i, val); ++i)
 189     {
 190       if (fd == val)
 191         {
 192           VEC_unordered_remove (int, open_fds, i);
 193           return;
 194         }
 195     }
 196
 197   gdb_assert_not_reached (_("fd not found in open_fds"));
 198 }
 199
 200 /* Helper function for close_most_fds that closes the file descriptor
 201    if appropriate.  */
 202
 203 static int
 204 do_close (void *ignore, int fd)
 205 {
 206   int i, val;
 207
 208   for (i = 0; VEC_iterate (int, open_fds, i, val); ++i)
 209     {
 210       if (fd == val)
 211         {
 212           /* Keep this one open.  */
 213           return 0;
 214         }
 215     }
 216
 217   close (fd);
 218   return 0;
 219 }
 220
 221 /* See filestuff.h.  */
 222
 223 void
 224 close_most_fds (void)
 225 {
 226   fdwalk (do_close, NULL);
 227 }
 228
 229 \f
 230
 231 /* This is a tri-state flag.  When zero it means we haven't yet tried
 232    O_CLOEXEC.  When positive it means that O_CLOEXEC works on this
 233    host.  When negative, it means that O_CLOEXEC doesn't work.  We
 234    track this state because, while gdb might have been compiled
 235    against a libc that supplies O_CLOEXEC, there is no guarantee that
 236    the kernel supports it.  */
 237
 238 static int trust_o_cloexec;
 239
 240 /* Mark FD as close-on-exec, ignoring errors.  Update
 241    TRUST_O_CLOEXEC.  */
 242
 243 static void
 244 mark_cloexec (int fd)
 245 {
 246 #ifdef HAVE_F_GETFD
 247   int old = fcntl (fd, F_GETFD, 0);
 248
 249   if (old != -1)
 250     {
 251       fcntl (fd, F_SETFD, old | FD_CLOEXEC);
 252
 253       if (trust_o_cloexec == 0)
 254         {
 255           if ((old & FD_CLOEXEC) != 0)
 256             trust_o_cloexec = 1;
 257           else
 258             trust_o_cloexec = -1;
 259         }
 260     }
 261 #endif /* HAVE_F_GETFD */
 262 }
 263
 264 /* Depending on TRUST_O_CLOEXEC, mark FD as close-on-exec.  */
 265
 266 static void
 267 maybe_mark_cloexec (int fd)
 268 {
 269   if (trust_o_cloexec <= 0)
 270     mark_cloexec (fd);
 271 }
 272
 273 #ifdef HAVE_SOCKETS
 274
 275 /* Like maybe_mark_cloexec, but for callers that use SOCK_CLOEXEC.  */
 276
 277 static void
 278 socket_mark_cloexec (int fd)
 279 {
 280   if (SOCK_CLOEXEC == 0 || trust_o_cloexec <= 0)
 281     mark_cloexec (fd);
 282 }
 283
 284 #endif
 285
 286 \f
 287
 288 /* See filestuff.h.  */
 289
 290 int
 291 gdb_open_cloexec (const char *filename, int flags, unsigned long mode)
 292 {
 293   int fd = open (filename, flags | O_CLOEXEC, mode);
 294
 295   if (fd >= 0)
 296     maybe_mark_cloexec (fd);
 297
 298   return fd;
 299 }
 300
 301 /* See filestuff.h.  */
 302
 303 FILE *
 304 gdb_fopen_cloexec (const char *filename, const char *opentype)
 305 {
 306   FILE *result;
 307   /* Probe for "e" support once.  But, if we can tell the operating
 308      system doesn't know about close on exec mode "e" without probing,
 309      skip it.  E.g., the Windows runtime issues an "Invalid parameter
 310      passed to C runtime function" OutputDebugString warning for
 311      unknown modes.  Assume that if O_CLOEXEC is zero, then "e" isn't
 312      supported.  */
 313   static int fopen_e_ever_failed_einval = O_CLOEXEC == 0;
 314
 315   if (!fopen_e_ever_failed_einval)
 316     {
 317       char *copy;
 318
 319       copy = (char *) alloca (strlen (opentype) + 2);
 320       strcpy (copy, opentype);
 321       /* This is a glibc extension but we try it unconditionally on
 322          this path.  */
 323       strcat (copy, "e");
 324       result = fopen (filename, copy);
 325
 326       if (result == NULL && errno == EINVAL)
 327         {
 328           result = fopen (filename, opentype);
 329           if (result != NULL)
 330             fopen_e_ever_failed_einval = 1;
 331         }
 332     }
 333   else
 334     result = fopen (filename, opentype);
 335
 336   if (result != NULL)
 337     maybe_mark_cloexec (fileno (result));
 338
 339   return result;
 340 }
 341
 342 #ifdef HAVE_SOCKETS
 343 /* See filestuff.h.  */
 344
 345 int
 346 gdb_socketpair_cloexec (int domain, int style, int protocol,
 347                         int filedes[2])
 348 {
 349 #ifdef HAVE_SOCKETPAIR
 350   int result = socketpair (domain, style | SOCK_CLOEXEC, protocol, filedes);
 351
 352   if (result != -1)
 353     {
 354       socket_mark_cloexec (filedes[0]);
 355       socket_mark_cloexec (filedes[1]);
 356     }
 357
 358   return result;
 359 #else
 360   gdb_assert_not_reached (_("socketpair not available on this host"));
 361 #endif
 362 }
 363
 364 /* See filestuff.h.  */
 365
 366 int
 367 gdb_socket_cloexec (int domain, int style, int protocol)
 368 {
 369   int result = socket (domain, style | SOCK_CLOEXEC, protocol);
 370
 371   if (result != -1)
 372     socket_mark_cloexec (result);
 373
 374   return result;
 375 }
 376 #endif
 377
 378 /* See filestuff.h.  */
 379
 380 int
 381 gdb_pipe_cloexec (int filedes[2])
 382 {
 383   int result;
 384
 385 #ifdef HAVE_PIPE2
 386   result = pipe2 (filedes, O_CLOEXEC);
 387   if (result != -1)
 388     {
 389       maybe_mark_cloexec (filedes[0]);
 390       maybe_mark_cloexec (filedes[1]);
 391     }
 392 #else
 393 #ifdef HAVE_PIPE
 394   result = pipe (filedes);
 395   if (result != -1)
 396     {
 397       mark_cloexec (filedes[0]);
 398       mark_cloexec (filedes[1]);
 399     }
 400 #else /* HAVE_PIPE */
 401   gdb_assert_not_reached (_("pipe not available on this host"));
 402 #endif /* HAVE_PIPE */
 403 #endif /* HAVE_PIPE2 */
 404
 405   return result;
 406 }
 407
 408 /* Helper function which does the work for make_cleanup_close.  */
 409
 410 static void
 411 do_close_cleanup (void *arg)
 412 {
 413   int *fd = (int *) arg;
 414
 415   close (*fd);
 416 }
 417
 418 /* See filestuff.h.  */
 419
 420 struct cleanup *
 421 make_cleanup_close (int fd)
 422 {
 423   int *saved_fd = XNEW (int);
 424
 425   *saved_fd = fd;
 426   return make_cleanup_dtor (do_close_cleanup, saved_fd, xfree);
 427 }