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Re: [Qemu-devel] [PATCH v2] qga: add systemd socket activation support
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH v2] qga: add systemd socket activation support |
Date: |
Thu, 12 Jan 2017 14:43:56 +0000 |
User-agent: |
Mutt/1.7.1 (2016-10-04) |
On Fri, Jan 06, 2017 at 03:29:30PM +0000, Stefan Hajnoczi wrote:
> AF_UNIX and AF_VSOCK listen sockets can be passed in by systemd on
> startup. This allows systemd to manage the listen socket until the
> first client connects and between restarts. Advantages of socket
> activation are that parallel startup of network services becomes
> possible and that unused daemons do not consume memory.
>
> The key to achieving this is the LISTEN_FDS environment variable, which
> is a stable ABI as shown here:
> https://www.freedesktop.org/wiki/Software/systemd/InterfacePortabilityAndStabilityChart/
>
> We could link against libsystemd and use sd_listen_fds(3) but it's easy
> to implement the tiny LISTEN_FDS ABI so that qemu-ga does not depend on
> libsystemd. Some systems may not have systemd installed and wish to
> avoid the dependency. Other init systems or socket activation servers
> may implement the same ABI without systemd involvement.
>
> Test as follows:
>
> $ cat ~/.config/systemd/user/qga.service
> [Unit]
> Description=qga
>
> [Service]
> WorkingDirectory=/tmp
> ExecStart=/path/to/qemu-ga --logfile=/tmp/qga.log --pidfile=/tmp/qga.pid
> --statedir=/tmp
>
> $ cat ~/.config/systemd/user/qga.socket
> [Socket]
> ListenStream=/tmp/qga.sock
>
> [Install]
> WantedBy=default.target
>
> $ systemctl --user daemon-reload
> $ systemctl --user start qga.socket
> $ nc -U /tmp/qga.sock
>
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
> v2:
> * Drop libsystemd dependency [danpb]
>
> qga/channel.h | 3 ++-
> qga/channel-posix.c | 66 ++++++++++++++++++++++++++---------------------
> qga/channel-win32.c | 2 +-
> qga/main.c | 74
> +++++++++++++++++++++++++++++++++++++++++++++++++----
> 4 files changed, 109 insertions(+), 36 deletions(-)
Ping: Mike
BTW systemd have merged AF_VSOCK socket activation support:
https://github.com/systemd/systemd/commit/84e6712f946dd0d08102bf75eebd2852829408ae
> diff --git a/qga/channel.h b/qga/channel.h
> index 8fd0c8f..1778416 100644
> --- a/qga/channel.h
> +++ b/qga/channel.h
> @@ -25,7 +25,8 @@ typedef enum {
> typedef gboolean (*GAChannelCallback)(GIOCondition condition, gpointer
> opaque);
>
> GAChannel *ga_channel_new(GAChannelMethod method, const gchar *path,
> - GAChannelCallback cb, gpointer opaque);
> + int listen_fd, GAChannelCallback cb,
> + gpointer opaque);
> void ga_channel_free(GAChannel *c);
> GIOStatus ga_channel_read(GAChannel *c, gchar *buf, gsize size, gsize
> *count);
> GIOStatus ga_channel_write_all(GAChannel *c, const gchar *buf, gsize size);
> diff --git a/qga/channel-posix.c b/qga/channel-posix.c
> index 71582e0..3f34465 100644
> --- a/qga/channel-posix.c
> +++ b/qga/channel-posix.c
> @@ -118,14 +118,16 @@ static int ga_channel_client_add(GAChannel *c, int fd)
> return 0;
> }
>
> -static gboolean ga_channel_open(GAChannel *c, const gchar *path,
> GAChannelMethod method)
> +static gboolean ga_channel_open(GAChannel *c, const gchar *path,
> + GAChannelMethod method, int fd)
> {
> int ret;
> c->method = method;
>
> switch (c->method) {
> case GA_CHANNEL_VIRTIO_SERIAL: {
> - int fd = qemu_open(path, O_RDWR | O_NONBLOCK
> + assert(fd < 0);
> + fd = qemu_open(path, O_RDWR | O_NONBLOCK
> #ifndef CONFIG_SOLARIS
> | O_ASYNC
> #endif
> @@ -153,7 +155,9 @@ static gboolean ga_channel_open(GAChannel *c, const gchar
> *path, GAChannelMethod
> }
> case GA_CHANNEL_ISA_SERIAL: {
> struct termios tio;
> - int fd = qemu_open(path, O_RDWR | O_NOCTTY | O_NONBLOCK);
> +
> + assert(fd < 0);
> + fd = qemu_open(path, O_RDWR | O_NOCTTY | O_NONBLOCK);
> if (fd == -1) {
> g_critical("error opening channel: %s", strerror(errno));
> return false;
> @@ -183,37 +187,41 @@ static gboolean ga_channel_open(GAChannel *c, const
> gchar *path, GAChannelMethod
> break;
> }
> case GA_CHANNEL_UNIX_LISTEN: {
> - Error *local_err = NULL;
> - int fd = unix_listen(path, NULL, strlen(path), &local_err);
> - if (local_err != NULL) {
> - g_critical("%s", error_get_pretty(local_err));
> - error_free(local_err);
> - return false;
> + if (fd < 0) {
> + Error *local_err = NULL;
> +
> + fd = unix_listen(path, NULL, strlen(path), &local_err);
> + if (local_err != NULL) {
> + g_critical("%s", error_get_pretty(local_err));
> + error_free(local_err);
> + return false;
> + }
> }
> ga_channel_listen_add(c, fd, true);
> break;
> }
> case GA_CHANNEL_VSOCK_LISTEN: {
> - Error *local_err = NULL;
> - SocketAddress *addr;
> - char *addr_str;
> - int fd;
> + if (fd < 0) {
> + Error *local_err = NULL;
> + SocketAddress *addr;
> + char *addr_str;
>
> - addr_str = g_strdup_printf("vsock:%s", path);
> - addr = socket_parse(addr_str, &local_err);
> - g_free(addr_str);
> - if (local_err != NULL) {
> - g_critical("%s", error_get_pretty(local_err));
> - error_free(local_err);
> - return false;
> - }
> + addr_str = g_strdup_printf("vsock:%s", path);
> + addr = socket_parse(addr_str, &local_err);
> + g_free(addr_str);
> + if (local_err != NULL) {
> + g_critical("%s", error_get_pretty(local_err));
> + error_free(local_err);
> + return false;
> + }
>
> - fd = socket_listen(addr, &local_err);
> - qapi_free_SocketAddress(addr);
> - if (local_err != NULL) {
> - g_critical("%s", error_get_pretty(local_err));
> - error_free(local_err);
> - return false;
> + fd = socket_listen(addr, &local_err);
> + qapi_free_SocketAddress(addr);
> + if (local_err != NULL) {
> + g_critical("%s", error_get_pretty(local_err));
> + error_free(local_err);
> + return false;
> + }
> }
> ga_channel_listen_add(c, fd, true);
> break;
> @@ -262,13 +270,13 @@ GIOStatus ga_channel_read(GAChannel *c, gchar *buf,
> gsize size, gsize *count)
> }
>
> GAChannel *ga_channel_new(GAChannelMethod method, const gchar *path,
> - GAChannelCallback cb, gpointer opaque)
> + int listen_fd, GAChannelCallback cb, gpointer
> opaque)
> {
> GAChannel *c = g_new0(GAChannel, 1);
> c->event_cb = cb;
> c->user_data = opaque;
>
> - if (!ga_channel_open(c, path, method)) {
> + if (!ga_channel_open(c, path, method, listen_fd)) {
> g_critical("error opening channel");
> ga_channel_free(c);
> return NULL;
> diff --git a/qga/channel-win32.c b/qga/channel-win32.c
> index 21f9dee..7e6dc4d 100644
> --- a/qga/channel-win32.c
> +++ b/qga/channel-win32.c
> @@ -316,7 +316,7 @@ static gboolean ga_channel_open(GAChannel *c,
> GAChannelMethod method,
> }
>
> GAChannel *ga_channel_new(GAChannelMethod method, const gchar *path,
> - GAChannelCallback cb, gpointer opaque)
> + int listen_fd, GAChannelCallback cb, gpointer
> opaque)
> {
> GAChannel *c = g_new0(GAChannel, 1);
> SECURITY_ATTRIBUTES sec_attrs;
> diff --git a/qga/main.c b/qga/main.c
> index 6caf215..4da8246 100644
> --- a/qga/main.c
> +++ b/qga/main.c
> @@ -28,6 +28,7 @@
> #include "qga/channel.h"
> #include "qemu/bswap.h"
> #include "qemu/help_option.h"
> +#include "qemu/sockets.h"
> #ifdef _WIN32
> #include "qga/service-win32.h"
> #include "qga/vss-win32.h"
> @@ -184,6 +185,37 @@ void reopen_fd_to_null(int fd)
> }
> #endif
>
> +/**
> + * get_listen_fd:
> + * @consume: true to prevent future calls from succeeding
> + *
> + * Fetch a listen file descriptor that was passed via systemd socket
> + * activation. Use @consume to prevent child processes from thinking a file
> + * descriptor was passed.
> + *
> + * Returns: file descriptor or -1 if no fd was passed
> + */
> +static int get_listen_fd(bool consume)
> +{
> +#ifdef _WIN32
> + return -1; /* no fd passing expected, unsetenv(3) not available */
> +#else
> + const char *listen_fds = getenv("LISTEN_FDS");
> + int fd = STDERR_FILENO + 1;
> +
> + if (!listen_fds || strcmp(listen_fds, "1") != 0) {
> + return -1;
> + }
> +
> + if (consume) {
> + unsetenv("LISTEN_FDS");
> + }
> +
> + qemu_set_cloexec(fd);
> + return fd;
> +#endif /* !_WIN32 */
> +}
> +
> static void usage(const char *cmd)
> {
> printf(
> @@ -648,7 +680,8 @@ static gboolean channel_event_cb(GIOCondition condition,
> gpointer data)
> return true;
> }
>
> -static gboolean channel_init(GAState *s, const gchar *method, const gchar
> *path)
> +static gboolean channel_init(GAState *s, const gchar *method, const gchar
> *path,
> + int listen_fd)
> {
> GAChannelMethod channel_method;
>
> @@ -666,7 +699,8 @@ static gboolean channel_init(GAState *s, const gchar
> *method, const gchar *path)
> return false;
> }
>
> - s->channel = ga_channel_new(channel_method, path, channel_event_cb, s);
> + s->channel = ga_channel_new(channel_method, path, listen_fd,
> + channel_event_cb, s);
> if (!s->channel) {
> g_critical("failed to create guest agent channel");
> return false;
> @@ -1025,7 +1059,9 @@ static void config_dump(GAConfig *config)
>
> g_key_file_set_boolean(keyfile, "general", "daemon", config->daemonize);
> g_key_file_set_string(keyfile, "general", "method", config->method);
> - g_key_file_set_string(keyfile, "general", "path", config->channel_path);
> + if (config->channel_path) {
> + g_key_file_set_string(keyfile, "general", "path",
> config->channel_path);
> + }
> if (config->log_filepath) {
> g_key_file_set_string(keyfile, "general", "logfile",
> config->log_filepath);
> @@ -1294,7 +1330,9 @@ static int run_agent(GAState *s, GAConfig *config)
> #endif
>
> s->main_loop = g_main_loop_new(NULL, false);
> - if (!channel_init(ga_state, config->method, config->channel_path)) {
> +
> + if (!channel_init(ga_state, config->method, config->channel_path,
> + get_listen_fd(true))) {
> g_critical("failed to initialize guest agent channel");
> return EXIT_FAILURE;
> }
> @@ -1318,6 +1356,7 @@ int main(int argc, char **argv)
> int ret = EXIT_SUCCESS;
> GAState *s = g_new0(GAState, 1);
> GAConfig *config = g_new0(GAConfig, 1);
> + int listen_fd;
>
> config->log_level = G_LOG_LEVEL_ERROR | G_LOG_LEVEL_CRITICAL;
>
> @@ -1339,7 +1378,32 @@ int main(int argc, char **argv)
> config->method = g_strdup("virtio-serial");
> }
>
> - if (config->channel_path == NULL) {
> + listen_fd = get_listen_fd(false);
> + if (listen_fd >= 0) {
> + SocketAddress *addr;
> +
> + g_free(config->method);
> + g_free(config->channel_path);
> + config->method = NULL;
> + config->channel_path = NULL;
> +
> + addr = socket_local_address(listen_fd, NULL);
> + if (addr) {
> + if (addr->type == SOCKET_ADDRESS_KIND_UNIX) {
> + config->method = g_strdup("unix-listen");
> + } else if (addr->type == SOCKET_ADDRESS_KIND_VSOCK) {
> + config->method = g_strdup("vsock-listen");
> + }
> +
> + qapi_free_SocketAddress(addr);
> + }
> +
> + if (!config->method) {
> + g_critical("unsupported listen fd type");
> + ret = EXIT_FAILURE;
> + goto end;
> + }
> + } else if (config->channel_path == NULL) {
> if (strcmp(config->method, "virtio-serial") == 0) {
> /* try the default path for the virtio-serial port */
> config->channel_path = g_strdup(QGA_VIRTIO_PATH_DEFAULT);
> --
> 2.9.3
>
>
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