diff options
Diffstat (limited to 'src/shared')
| -rw-r--r-- | src/shared/eventfd-util.c | 169 | ||||
| -rw-r--r-- | src/shared/eventfd-util.h | 43 |
2 files changed, 212 insertions, 0 deletions
diff --git a/src/shared/eventfd-util.c b/src/shared/eventfd-util.c new file mode 100644 index 0000000000..27b7cf788f --- /dev/null +++ b/src/shared/eventfd-util.c @@ -0,0 +1,169 @@ +/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/ + +/*** + This file is part of systemd. + + Copyright 2014 Djalal Harouni + + systemd is free software; you can redistribute it and/or modify it + under the terms of the GNU Lesser General Public License as published by + the Free Software Foundation; either version 2.1 of the License, or + (at your option) any later version. + + systemd 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 + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with systemd; If not, see <http://www.gnu.org/licenses/>. +***/ + +#include <assert.h> +#include <errno.h> +#include <unistd.h> +#include <sys/eventfd.h> +#include <sys/syscall.h> + +#include "eventfd-util.h" +#include "util.h" + + +/* + * Use this to create processes that need to setup a full context + * and sync it with their parents using cheap mechanisms. + * + * This will create two blocking eventfd(s). A pair for the parent and + * the other for the child so they can be used as a notify mechanism. + * Each process will gets its copy of the parent and child eventfds. + * + * This is useful in case: + * 1) If the parent fails or dies, the child must die. + * 2) Child will install PR_SET_PDEATHSIG as soon as possible. + * 3) Parent and child need to sync using less resources. + * 4) If parent is not able to install a SIGCHLD handler: + * parent will wait using a blocking eventfd_read() or + * eventfd_child_succeeded() call on the child eventfd. + * + * * If the child setup succeeded, child should notify with an + * EVENTFD_CHILD_SUCCEEDED, parent will continue. + * * If the child setup failed, child should notify with an + * EVENTFD_CHILD_FAILED before any _exit(). This avoids blocking + * the parent. + * + * 5) If parent is able to install a SIGCHLD handler: + * An empty signal handler without SA_RESTART will do it, since the + * blocking eventfd_read() or eventfd_parent_succeeded() of the + * parent will be interrupted by SIGCHLD and the call will fail with + * EINTR. This is useful in case the child dies abnormaly and did + * not have a chance to notify its parent using EVENTFD_CHILD_FAILED. + * + * 6) Call wait*() in the main instead of the signal handler in order + * to: 1) reduce side effects and 2) have a better handling for + * child termination in order to reduce various race conditions. + * + * + * The return value of clone_with_eventfd() is the same of clone(). + * On success the eventfds[] will contain the two eventfd(s). These + * file descriptors can be closed later with safe_close(). On failure, + * a negative value is returned in the caller's context, and errno will + * be set appropriately. + * + * Extra preliminary work: + * 1) Child can wait before starting its setup by using the + * eventfd_recv_start() call on the parent eventfd, in that case the + * parent must notify with EVENTFD_START, after doing any preliminary + * work. + * + * Note: this function depends on systemd internal functions + * safe_close() and it should be used only by direct binaries, no + * libraries. + */ +pid_t clone_with_eventfd(int flags, int eventfds[2]) { + pid_t pid; + + assert(eventfds); + + eventfds[0] = eventfd(EVENTFD_INIT, EFD_CLOEXEC); + if (eventfds[0] < 0) + return -1; + + eventfds[1] = eventfd(EVENTFD_INIT, EFD_CLOEXEC); + if (eventfds[1] < 0) + goto err_eventfd0; + + pid = syscall(__NR_clone, flags, NULL); + if (pid < 0) + goto err_eventfd1; + + return pid; + +err_eventfd1: + eventfds[1] = safe_close(eventfds[1]); +err_eventfd0: + eventfds[0] = safe_close(eventfds[0]); + return -1; +} + +int eventfd_send_state(int efd, eventfd_t s) { + return eventfd_write(efd, s); +} + +/* + * Receive an eventfd state on the eventfd file descriptor. + * + * If the third argument is set to a value other than zero, then this + * function will compare the received value with this argument and set + * the return value. + * + * On success return 0. On error, -1 will be returned, and errno will + * be set appropriately. + */ +int eventfd_recv_state(int efd, eventfd_t *e, eventfd_t s) { + int ret; + + ret = eventfd_read(efd, e); + if (ret < 0) + return ret; + else if (s != 0 && *e != s) { + errno = EINVAL; + return -1; + } + + return 0; +} + +/* + * Receive the EVENTFD_START state on the eventfd file descriptor. + * + * On Success return 0. On error, -1 will be returned, and errno will + * be set appropriately. + */ +int eventfd_recv_start(int efd) { + eventfd_t e = EVENTFD_INIT; + return eventfd_recv_state(efd, &e, EVENTFD_START); +} + +/* + * Receive the EVENTFD_PARENT_SUCCEEDED state on the eventfd file + * descriptor. + * + * On Success return 0. On error, -1 will be returned, and errno will + * be set appropriately. + */ +int eventfd_parent_succeeded(int efd) { + eventfd_t e = EVENTFD_INIT; + return eventfd_recv_state(efd, &e, EVENTFD_PARENT_SUCCEEDED); +} + +/* + * Receive the EVENTFD_CHILD_SUCCEEDED state on the eventfd file + * descriptor. + * + * On Success return 0. On error, -1 will be returned, and errno will + * be set appropriately. + */ +int eventfd_child_succeeded(int efd) { + eventfd_t e = EVENTFD_INIT; + return eventfd_recv_state(efd, &e, EVENTFD_CHILD_SUCCEEDED); +} diff --git a/src/shared/eventfd-util.h b/src/shared/eventfd-util.h new file mode 100644 index 0000000000..0120f0409e --- /dev/null +++ b/src/shared/eventfd-util.h @@ -0,0 +1,43 @@ +/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/ + +#pragma once + +/*** + This file is part of systemd. + + Copyright 2014 Djalal Harouni + + systemd is free software; you can redistribute it and/or modify it + under the terms of the GNU Lesser General Public License as published by + the Free Software Foundation; either version 2.1 of the License, or + (at your option) any later version. + + systemd 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 + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public License + along with systemd; If not, see <http://www.gnu.org/licenses/>. +***/ + +#include <sys/types.h> +#include <sys/eventfd.h> + +enum { + EVENTFD_INIT, + EVENTFD_START, + EVENTFD_PARENT_SUCCEEDED, + EVENTFD_PARENT_FAILED, + EVENTFD_CHILD_SUCCEEDED, + EVENTFD_CHILD_FAILED, +}; + +pid_t clone_with_eventfd(int flags, int eventfds[2]); + +int eventfd_send_state(int efd, eventfd_t s); +int eventfd_recv_state(int efd, eventfd_t *e, eventfd_t s); + +int eventfd_recv_start(int efd); +int eventfd_parent_succeeded(int efd); +int eventfd_child_succeeded(int efd); |