Initial commit.

src/trackfds.h

@@ -0,0 +1,179 @@
+/*
+ * Utility functions to track file descriptors.
+ *
+ * Copyright (C) 2013  Simon Ruderich
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef TRACKFDS_H
+#define TRACKFDS_H 1
+
+/* List of tracked file descriptors. */
+static int *tracked_fds;
+/* Current number of items in the list. */
+static size_t tracked_fds_count;
+/* Allocated items, used to reduce realloc()s. */
+static size_t tracked_fds_space;
+
+
+/* Load tracked file descriptors from the environment. The environment is used
+ * to pass the information to child processes.
+ *
+ * ENV_NAME_FDS has the following format: Each descriptor as string followed
+ * by a comma; there's a trailing comma. Example: "2,4,". */
+static void init_from_environment(void) {
+    tracked_fds_count = 0;
+
+    const char *env = getenv(ENV_NAME_FDS);
+    if (!env) {
+        return;
+    }
+    /* Environment is read-only. */
+    char *env_copy = strdup(env);
+    if (!env_copy) {
+        return;
+    }
+
+    char *x;
+
+    size_t count = 0;
+    for (x = env_copy; *x; x++) {
+        if (*x == ',') {
+            count++;
+        }
+    }
+    tracked_fds_space = count + TRACKFDS_REALLOC_STEP;
+
+    tracked_fds = malloc(tracked_fds_space * sizeof(*tracked_fds));
+    if (!tracked_fds) {
+        free(env_copy);
+        return;
+    }
+
+    size_t i = 0;
+
+    /* Parse file descriptor numbers from environment string and store them as
+     * integers in tracked_fds. */
+    char *last;
+    for (x = env_copy, last = env_copy; *x; x++) {
+        if (*x != ',') {
+            continue;
+        }
+        /* ',' at the beginning or double ',' - ignore. */
+        if (x == last) {
+            last = x + 1;
+            continue;
+        }
+
+        if (i == count) {
+            break;
+        }
+
+        *x = 0;
+        tracked_fds[i++] = atoi(last);
+
+        last = x + 1;
+    }
+
+    tracked_fds_count = count;
+
+    free(env_copy);
+}
+
+static void update_environment(void) {
+    /* An integer (32-bit) has at most 10 digits, + 1 for the comma after each
+     * number. Bigger file descriptors (which shouldn't occur in reality) are
+     * truncated. */
+    char env[tracked_fds_count * (10 + 1) * sizeof(char)];
+    char *x = env;
+
+    size_t i;
+    for (i = 0; i < tracked_fds_count; i++) {
+        int length = snprintf(x, 10 + 1, "%d", tracked_fds[i]);
+        if (length >= 10 + 1)
+            return;
+
+        /* Write comma after number. */
+        x += length;
+        *x++ = ',';
+        /* Make sure the string is always zero terminated. */
+        *x = 0;
+    }
+
+    setenv(ENV_NAME_FDS, env, 1 /* overwrite */);
+}
+
+
+#ifdef DEBUG
+static void tracked_fds_debug() {
+    debug("tracked_fds: %d/%d\n", tracked_fds_count, tracked_fds_space);
+    size_t i;
+    for (i = 0; i < tracked_fds_count; i++) {
+        debug("tracked_fds[%d]: %d\n", i, tracked_fds[i]);
+    }
+}
+#endif
+
+static void tracked_fds_add(int fd) {
+    if (tracked_fds_count >= tracked_fds_space) {
+        size_t new_space = tracked_fds_space + TRACKFDS_REALLOC_STEP;
+        if (!realloc(tracked_fds, sizeof(*tracked_fds) * new_space)) {
+            /* We can do nothing, just ignore the error. We made sure not to
+             * destroy our state, so the new descriptor is ignored without any
+             * other consequences. */
+            return;
+        }
+        tracked_fds_space = new_space;
+    }
+
+    tracked_fds[tracked_fds_count++] = fd;
+
+#ifdef DEBUG
+    tracked_fds_debug();
+#endif
+}
+static int tracked_fds_remove(int fd) {
+    size_t i;
+    for (i = 0; i < tracked_fds_count; i++) {
+        if (fd != tracked_fds[i]) {
+            continue;
+        }
+
+        memmove(tracked_fds + i, tracked_fds + i + 1,
+                sizeof(*tracked_fds) * (tracked_fds_count - i - 1));
+        tracked_fds_count--;
+
+#ifdef DEBUG
+        tracked_fds_debug();
+#endif
+
+        /* Found. */
+        return 1;
+    }
+
+    /* Not found. */
+    return 0;
+}
+static int tracked_fds_find(int fd) {
+    size_t i;
+    for (i = 0; i < tracked_fds_count; i++) {
+        if (fd == tracked_fds[i]) {
+            return 1;
+        }
+    }
+    return 0;
+}
+
+#endif