2 * Utility functions to track file descriptors.
4 * Copyright (C) 2013 Simon Ruderich
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.
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.
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/>.
23 /* Array of tracked file descriptors. Used for fast lookups for the normally
24 * used file descriptors (0 <= fd < TRACKFDS_STATIC_COUNT). */
25 static int tracked_fds[TRACKFDS_STATIC_COUNT];
27 /* List of tracked file descriptors >= TRACKFDS_STATIC_COUNT. */
28 static int *tracked_fds_list;
29 /* Current number of items in the list. */
30 static size_t tracked_fds_list_count;
31 /* Allocated items, used to reduce realloc()s. */
32 static size_t tracked_fds_list_space;
36 static void tracked_fds_debug(void) {
39 for (i = 0; i < TRACKFDS_STATIC_COUNT; i++) {
41 debug(" tracked_fds[%d]: %d\n", i, tracked_fds[i]);
44 debug(" tracked_fds_list: %d/%d\t[%d]\n", tracked_fds_list_count,
45 tracked_fds_list_space,
47 for (i = 0; i < tracked_fds_list_count; i++) {
48 debug(" tracked_fds_list[%d]: %d\n", i, tracked_fds_list[i]);
53 static int init_tracked_fds_list(size_t count) {
56 /* Reduce reallocs. */
57 count += TRACKFDS_REALLOC_STEP;
59 tracked_fds_list = malloc(count * sizeof(*tracked_fds_list));
60 if (!tracked_fds_list) {
62 warning("malloc(tracked_fds_list, %d) failed [%d]\n",
63 count * sizeof(*tracked_fds_list), getpid());
68 tracked_fds_list_space = count;
72 /* Load tracked file descriptors from the environment. The environment is used
73 * to pass the information to child processes.
75 * ENV_NAME_FDS and ENV_NAME_PRIVATE_FDS have the following format: Each
76 * descriptor as string followed by a comma; there's a trailing comma.
78 static void init_from_environment(void) {
80 debug("init_from_environment()\t\t[%d]\n", getpid());
84 int saved_errno = errno;
89 tracked_fds_list_count = 0;
91 /* If ENV_NAME_FORCE_WRITE is set and not empty, allow writes to a non-tty
92 * device. Use with care! Mainly used for the test suite. */
93 env = getenv(ENV_NAME_FORCE_WRITE);
94 if (env && env[0] != '\0') {
95 force_write_to_non_tty = 1;
98 /* Prefer user defined list of file descriptors, fall back to file
99 * descriptors passed through the environment from the parent process. */
100 env = getenv(ENV_NAME_FDS);
102 used_fds_set_by_user = 1;
104 env = getenv(ENV_NAME_PRIVATE_FDS);
111 debug(" getenv(\"%s\"): \"%s\"\n", ENV_NAME_FDS, env);
112 debug(" getenv(\"%s\"): \"%s\"\n", ENV_NAME_PRIVATE_FDS, env);
115 /* Environment must be treated read-only. */
116 char env_copy[strlen(env) + 1];
117 strcpy(env_copy, env);
122 for (x = env_copy; *x; x++) {
130 /* Parse file descriptor numbers from environment string and store them as
131 * integers in tracked_fds and tracked_fds_list. */
133 for (x = env_copy, last = env_copy; *x; x++) {
137 /* ',' at the beginning or double ',' - ignore. */
146 /* Replace ',' to null-terminate number for atoi(). */
153 } else if (fd < TRACKFDS_STATIC_COUNT) {
156 if (!tracked_fds_list) {
157 /* Pessimistic count estimate, but allocating a few more
158 * elements doesn't hurt. */
159 if (!init_tracked_fds_list(count)) {
160 /* Couldn't allocate memory, skip this entry. */
164 tracked_fds_list[i++] = fd;
166 debug(" large fd: %d\n", fd);
174 tracked_fds_list_count = i;
183 static char *update_environment_buffer_entry(char *x, int fd) {
186 int length = snprintf(x, 10 + 1, "%d", fd);
187 if (length >= 10 + 1 || length <= 0 /* shouldn't happen */) {
188 /* Integer too big to fit the buffer, skip it. */
190 warning("update_environment_buffer_entry(): truncated fd: %d [%d]\n",
196 /* Write comma after number. */
199 /* Make sure the string is always null-terminated. */
204 static void update_environment_buffer(char *x) {
208 for (i = 0; i < TRACKFDS_STATIC_COUNT; i++) {
209 if (tracked_fds[i]) {
210 x = update_environment_buffer_entry(x, (int)i);
213 for (i = 0; i < tracked_fds_list_count; i++) {
214 x = update_environment_buffer_entry(x, tracked_fds_list[i]);
217 inline static size_t update_environment_buffer_size(void) {
220 /* Use the maximum count (TRACKFDS_STATIC_COUNT) of used descriptors
221 * because it's simple and small enough not to be a problem.
223 * An integer (32-bit) has at most 10 digits, + 1 for the comma after each
224 * number. Bigger file descriptors (which shouldn't occur in reality) are
226 return (TRACKFDS_STATIC_COUNT + tracked_fds_list_count)
227 * (10 + 1) + 1 /* to fit '\0' */;
229 static void update_environment(void) {
231 debug("update_environment()\t\t[%d]\n", getpid());
234 /* If we haven't parsed the environment we also haven't modified it - so
240 int saved_errno = errno;
242 char env[update_environment_buffer_size()];
245 update_environment_buffer(env);
248 debug(" setenv(\"%s\", \"%s\", 1)\n", ENV_NAME_PRIVATE_FDS, env);
250 setenv(ENV_NAME_PRIVATE_FDS, env, 1 /* overwrite */);
252 /* Child processes must use ENV_NAME_PRIVATE_FDS to get the updated list
253 * of tracked file descriptors, not the static list provided by the user
256 * But only remove it if the static list in ENV_NAME_FDS was loaded by
257 * init_from_environment() and merged into ENV_NAME_PRIVATE_FDS. */
258 if (used_fds_set_by_user) {
259 unsetenv(ENV_NAME_FDS);
267 static void tracked_fds_add(int fd) {
270 if (fd < TRACKFDS_STATIC_COUNT) {
273 debug("tracked_fds_add(): %-3d\t\t[%d]\n", fd, getpid());
279 if (tracked_fds_list_count >= tracked_fds_list_space) {
280 int saved_errno = errno;
282 size_t new_space = tracked_fds_list_space + TRACKFDS_REALLOC_STEP;
283 int *tmp = realloc(tracked_fds_list,
284 sizeof(*tracked_fds_list) * new_space);
286 /* We can do nothing, just ignore the error. We made sure not to
287 * destroy our state, so the new descriptor is ignored without any
288 * other consequences. */
290 warning("realloc(tracked_fds_list, %zu) failed! [%d]\n",
291 sizeof(*tracked_fds_list) * new_space, getpid());
298 tracked_fds_list = tmp;
299 tracked_fds_list_space = new_space;
302 tracked_fds_list[tracked_fds_list_count++] = fd;
305 debug("tracked_fds_add(): %-3d\t\t[%d]\n", fd, getpid());
309 static int tracked_fds_remove(int fd) {
312 if (fd < TRACKFDS_STATIC_COUNT) {
313 int old_value = tracked_fds[fd];
317 debug("tracked_fds_remove(): %-3d\t[%d]\n", fd, getpid());
320 return old_value; /* Found vs. not found. */
324 for (i = 0; i < tracked_fds_list_count; i++) {
325 if (fd != tracked_fds_list[i]) {
329 memmove(tracked_fds_list + i, tracked_fds_list + i + 1,
330 sizeof(*tracked_fds_list) * (tracked_fds_list_count - i - 1));
331 tracked_fds_list_count--;
334 debug("tracked_fds_remove(): %-3d\t[%d]\n", fd, getpid());
346 static int tracked_fds_find_slow(int fd) noinline;
348 * tracked_fds_find() is called for each hook call and should be as fast as
349 * possible. As most file descriptors are < TRACKFDS_STATIC_COUNT, force the
350 * compiler to inline that part which is almost exclusively used.
352 * Inlining tracked_fds_add()/tracked_fds_remove() isn't worth the effort as
353 * they are not called often enough.
355 inline static int tracked_fds_find(int fd) always_inline;
356 inline static int tracked_fds_find(int fd) {
357 /* Invalid file descriptor. No assert() as we're called from the hooked
359 if (unlikely(fd < 0)) {
363 if (fd < TRACKFDS_STATIC_COUNT) {
364 return tracked_fds[fd];
367 return tracked_fds_find_slow(fd);
369 static int tracked_fds_find_slow(int fd) {
373 if (tracked_fds_list_count == 0) {
378 for (i = 0; i < tracked_fds_list_count; i++) {
379 if (fd == tracked_fds_list[i]) {