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qga: add systemd socket activation support
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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 <[email protected]>
Reviewed-by: Daniel P. Berrange <[email protected]>
Signed-off-by: Michael Roth <[email protected]>
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stefanhaRH authored and mdroth committed Mar 6, 2017
1 parent 17783ac commit 26de229
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Showing 4 changed files with 110 additions and 37 deletions.
68 changes: 38 additions & 30 deletions qga/channel-posix.c
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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;

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;
}
if (fd < 0) {
Error *local_err = NULL;
SocketAddress *addr;
char *addr_str;

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;
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;
}
}
ga_channel_listen_add(c, fd, true);
break;
Expand Down Expand Up @@ -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;
Expand Down
2 changes: 1 addition & 1 deletion qga/channel-win32.c
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down
3 changes: 2 additions & 1 deletion qga/channel.h
Original file line number Diff line number Diff line change
Expand Up @@ -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);
Expand Down
74 changes: 69 additions & 5 deletions qga/main.c
Original file line number Diff line number Diff line change
Expand Up @@ -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"
Expand Down Expand Up @@ -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(
Expand Down Expand Up @@ -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;

Expand All @@ -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;
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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;
}
Expand All @@ -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;

Expand All @@ -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);
Expand Down

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