This adapts programs using sd_notify for use with s6 readiness notification. stdin and stdout are hard-coded for simplicity. Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com> --- systemd readiness notification has two strict advantages over the s6 version: 1. It allows reliable reloading. 2. It allows providing a status message that the service manager can show in status output. s6 would actually benefit from both of these features. --- Changes since v4: - Use CC0 for the trivial Meson file. - Use -D_GNU_SOURCE instead of #define _GNU_SOURCE 1. - Use a global variable for the iovec. - Use ISC license for the C code in case s6 wants to use it. - Remove unneeded MSG_DONTWAIT. - Remove unneeded check for EAGAIN and EWOULDBLOCK when poll() has already indicated that the file descriptor is ready. Changes since v1: - Hard-code file descriptors. - Run wrapper as background process. - Massively reduce code size. - Use // instead of /* */ for comments. - Check that the notification FD is a pipe and that the listening socket is a socket. - Rely on s6-ipc-socketbinder to create the listening socket. - Do not unlink the listening socket. Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com> --- tools/default.nix | 1 + tools/meson.build | 1 + tools/sd-notify-adapter/meson.build | 4 ++ tools/sd-notify-adapter/sd-notify-adapter.c | 107 ++++++++++++++++++++++++++++ 4 files changed, 113 insertions(+) diff --git a/tools/default.nix b/tools/default.nix index 398f57038d3f9fdec47b72850755e289f225f339..36a9a8c84de9f83e31981d3d47fab27e98f6ae5a 100644 --- a/tools/default.nix +++ b/tools/default.nix @@ -76,6 +76,7 @@ stdenv.mkDerivation (finalAttrs: { ./lsvm ./start-vmm ./subprojects + ./sd-notify-adapter ] ++ lib.optionals driverSupport [ ./xdp-forwarder ])); diff --git a/tools/meson.build b/tools/meson.build index 186008dbc9dd2b63adbce7475c375fb0de5c2c6a..5d0ae81042fd3d77646594500f32cb1d48a6af0c 100644 --- a/tools/meson.build +++ b/tools/meson.build @@ -27,6 +27,7 @@ if get_option('host') subdir('lsvm') subdir('start-vmm') + subdir('sd-notify-adapter') endif if get_option('app') diff --git a/tools/sd-notify-adapter/meson.build b/tools/sd-notify-adapter/meson.build new file mode 100644 index 0000000000000000000000000000000000000000..906fbde673105fd65436b34802f1bcc74e9f823e --- /dev/null +++ b/tools/sd-notify-adapter/meson.build @@ -0,0 +1,4 @@ +# SPDX-License-Identifier: CC0-1.0 +# SPDX-FileCopyrightText: 2025 Demi Marie Obenour <demiobenour@gmail.com> + +executable('sd-notify-adapter', 'sd-notify-adapter.c', c_args : ['-D_GNU_SOURCE'], install: true) diff --git a/tools/sd-notify-adapter/sd-notify-adapter.c b/tools/sd-notify-adapter/sd-notify-adapter.c new file mode 100644 index 0000000000000000000000000000000000000000..734f018da605e4359d3fa6422a01effbd9e878ea --- /dev/null +++ b/tools/sd-notify-adapter/sd-notify-adapter.c @@ -0,0 +1,107 @@ +// SPDX-License-Identifier: ISC +// SPDX-FileCopyrightText: 2025 Demi Marie Obenour <demiobenour@gmail.com> + +#include <assert.h> +#include <errno.h> +#include <limits.h> +#include <signal.h> +#include <stdarg.h> +#include <stddef.h> +#include <stdint.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> + +#include <err.h> +#include <fcntl.h> +#include <poll.h> +#include <sys/socket.h> +#include <sys/stat.h> +#include <sys/un.h> +#include <unistd.h> + +#define ARRAY_SIZE(s) (sizeof(s)/sizeof(s[0])) + +enum { + socket_fd, + notification_fd, +}; + +struct iovec msg; + +#define READY "READY=1" +#define READY_SIZE (sizeof(READY) - 1) + +static void process_notification(void) +{ + ssize_t first_recv_size = recv(socket_fd, msg.iov_base, msg.iov_len, + MSG_TRUNC | MSG_PEEK); + if (first_recv_size == -1) { + if (errno == EINTR) + return; // signal caught + err(EXIT_FAILURE, "recv from notification socket"); + } + size_t size = (size_t)first_recv_size; + if (size == 0) + return; // avoid arithmetic on NULL pointer + if (size > msg.iov_len) { + msg.iov_base = realloc(msg.iov_base, size); + if (msg.iov_base == NULL) + err(EXIT_FAILURE, "allocation failure"); + msg.iov_len = size; + } + ssize_t second_recv_size = recv(socket_fd, msg.iov_base, msg.iov_len, + MSG_CMSG_CLOEXEC | MSG_TRUNC); + if (second_recv_size == -1) { + if (errno == EINTR) + return; + err(EXIT_FAILURE, "recv from notification socket"); + } + assert(first_recv_size == second_recv_size); + for (char *next, *cursor = msg.iov_base, *end = cursor + size; + cursor != NULL; cursor = (next == NULL ? NULL : next + 1)) { + next = memchr(cursor, '\n', (size_t)(end - cursor)); + size_t message_size = (size_t)((next == NULL ? end : next) - cursor); + if (message_size == READY_SIZE && + memcmp(cursor, READY, READY_SIZE) == 0) { + ssize_t write_size = write(notification_fd, "\n", 1); + if (write_size != 1) + err(EXIT_FAILURE, "writing to notification descriptor"); + exit(0); + } + } +} + +int main(int argc, char **) +{ + if (argc != 1) + errx(EXIT_FAILURE, "stdin is listening socket, stdout is notification pipe"); + for (;;) { + struct pollfd p[] = { + { + .fd = socket_fd, + .events = POLLIN, + .revents = 0, + }, + { + .fd = notification_fd, + .events = 0, + .revents = 0, + }, + }; + int r = poll(p, ARRAY_SIZE(p), -1); + if (r < 0) { + if (errno == EINTR) + continue; + err(EXIT_FAILURE, "poll"); + } + if (p[0].revents) { + if (p[0].revents & POLLERR) + errx(EXIT_FAILURE, "unexpected POLLERR"); + if (p[0].revents & POLLIN) + process_notification(); + } + if (p[1].revents) + errx(EXIT_FAILURE, "s6 closed its pipe before the child was ready"); + } +} -- 2.51.2