Socket activation (sometimes known as systemd socket activation)
allows an Internet superserver to pass a pre-opened listening socket
to the process, instead of having qemu-nbd open a socket itself. This
is done via the LISTEN_FDS and LISTEN_PID environment variables, and a
standard file descriptor range.
This change partially implements socket activation for qemu-nbd. If
the environment variables are set correctly, then socket activation
will happen automatically, otherwise everything works as before. The
limitation is that LISTEN_FDS must be 1.
Signed-off-by: Richard W.M. Jones.
---
qemu-nbd.c | 172 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 163 insertions(+), 9 deletions(-)
diff --git a/qemu-nbd.c b/qemu-nbd.c
index c734f62..e4fede6 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -463,6 +463,135 @@ static QCryptoTLSCreds *nbd_get_tls_creds(const char *id, Error **errp)
return creds;
}
+static void setup_address_and_port(const char **address, const char **port)
+{
+ if (*address == NULL) {
+ *address = "0.0.0.0";
+ }
+
+ if (*port == NULL) {
+ *port = stringify(NBD_DEFAULT_PORT);
+ }
+}
+
+#define FIRST_SOCKET_ACTIVATION_FD 3 /* defined by systemd ABI */
+
+#ifndef _WIN32
+/*
+ * Check if socket activation was requested via use of the
+ * LISTEN_FDS and LISTEN_PID environment variables.
+ *
+ * Returns 0 if no socket activation, or the number of FDs.
+ */
+static unsigned int check_socket_activation(void)
+{
+ const char *s;
+ unsigned long pid;
+ unsigned long nr_fds;
+ unsigned int i;
+ int fd;
+ int err;
+
+ s = getenv("LISTEN_PID");
+ if (s == NULL) {
+ return 0;
+ }
+ err = qemu_strtoul(s, NULL, 10, &pid);
+ if (err) {
+ if (verbose) {
+ fprintf(stderr, "malformed %s environment variable (ignored)\n",
+ "LISTEN_PID");
+ }
+ return 0;
+ }
+ if (pid != getpid()) {
+ if (verbose) {
+ fprintf(stderr, "%s was not for us (ignored)\n",
+ "LISTEN_PID");
+ }
+ return 0;
+ }
+
+ s = getenv("LISTEN_FDS");
+ if (s == NULL) {
+ return 0;
+ }
+ err = qemu_strtoul(s, NULL, 10, &nr_fds);
+ if (err) {
+ if (verbose) {
+ fprintf(stderr, "malformed %s environment variable (ignored)\n",
+ "LISTEN_FDS");
+ }
+ return 0;
+ }
+ assert(nr_fds <= UINT_MAX);
+
+ /* A limitation of current qemu-nbd is that it can only listen on
+ * a single socket. When that limitation is lifted, we can change
+ * this function to allow LISTEN_FDS > 1, and remove the assertion
+ * in the main function below.
+ */
+ if (nr_fds > 1) {
+ error_report("qemu-nbd does not support socket activation with %s > 1",
+ "LISTEN_FDS");
+ exit(EXIT_FAILURE);
+ }
+
+ /* So these are not passed to any child processes we might start. */
+ unsetenv("LISTEN_FDS");
+ unsetenv("LISTEN_PID");
+
+ /* So the file descriptors don't leak into child processes. */
+ for (i = 0; i < nr_fds; ++i) {
+ fd = FIRST_SOCKET_ACTIVATION_FD + i;
+ if (fcntl(fd, F_SETFD, FD_CLOEXEC) == -1) {
+ /* If we cannot set FD_CLOEXEC then it probably means the file
+ * descriptor is invalid, so socket activation has gone wrong
+ * and we should exit.
+ */
+ error_report("Socket activation failed: "
+ "invalid file descriptor fd = %d: %m",
+ fd);
+ exit(EXIT_FAILURE);
+ }
+ }
+
+ return (unsigned int) nr_fds;
+}
+
+#else /* !_WIN32 */
+static unsigned int check_socket_activation(void)
+{
+ return 0;
+}
+#endif
+
+/*
+ * Check socket parameters compatibility when socket activation is used.
+ */
+static const char *socket_activation_validate_opts(const char *device,
+ const char *sockpath,
+ const char *address,
+ const char *port)
+{
+ if (device != NULL) {
+ return "NBD device can't be set when using socket activation";
+ }
+
+ if (sockpath != NULL) {
+ return "Unix socket can't be set when using socket activation";
+ }
+
+ if (address != NULL) {
+ return "The interface can't be set when using socket activation";
+ }
+
+ if (port != NULL) {
+ return "TCP port number can't be set when using socket activation";
+ }
+
+ return NULL;
+}
int main(int argc, char **argv)
{
@@ -471,7 +600,7 @@ int main(int argc, char **argv)
off_t dev_offset = 0;
uint16_t nbdflags = 0;
bool disconnect = false;
- const char *bindto = "0.0.0.0";
+ const char *bindto = NULL;
const char *port = NULL;
char *sockpath = NULL;
char *device = NULL;
@@ -533,6 +662,7 @@ int main(int argc, char **argv)
char *trace_file = NULL;
bool fork_process = false;
int old_stderr = -1;
+ unsigned socket_activation;
/* The client thread uses SIGTERM to interrupt the server. A signal
* handler ensures that "qemu-nbd -v -c" exits with a nice status code.
@@ -751,6 +881,19 @@ int main(int argc, char **argv)
trace_init_file(trace_file);
qemu_set_log(LOG_TRACE);
+ socket_activation = check_socket_activation();
+ if (socket_activation == 0) {
+ setup_address_and_port(&bindto, &port);
+ } else {
+ /* Using socket activation - check user didn't use -p etc. */
+ const char *err_msg = socket_activation_validate_opts(device, sockpath,
+ bindto, port);
+ if (err_msg != NULL) {
+ error_report("%s", err_msg);
+ exit(EXIT_FAILURE);
+ }
+ }
+
if (tlscredsid) {
if (sockpath) {
error_report("TLS is only supported with IPv4/IPv6");
@@ -855,7 +998,25 @@ int main(int argc, char **argv)
snprintf(sockpath, 128, SOCKET_PATH, basename(device));
}
- saddr = nbd_build_socket_address(sockpath, bindto, port);
+ if (socket_activation == 0) {
+ server_ioc = qio_channel_socket_new();
+ saddr = nbd_build_socket_address(sockpath, bindto, port);
+ if (qio_channel_socket_listen_sync(server_ioc, saddr, &local_err) < 0) {
+ object_unref(OBJECT(server_ioc));
+ error_report_err(local_err);
+ return 1;
+ }
+ } else {
+ /* See comment in check_socket_activation above. */
+ assert(socket_activation == 1);
+ server_ioc = qio_channel_socket_new_fd(FIRST_SOCKET_ACTIVATION_FD,
+ &local_err);
+ if (server_ioc == NULL) {
+ error_report("Failed to use socket activation: %s",
+ error_get_pretty(local_err));
+ exit(EXIT_FAILURE);
+ }
+ }
if (qemu_init_main_loop(&local_err)) {
error_report_err(local_err);
@@ -950,13 +1111,6 @@ int main(int argc, char **argv)
exit(EXIT_FAILURE);
}
- server_ioc = qio_channel_socket_new();
- if (qio_channel_socket_listen_sync(server_ioc, saddr, &local_err) < 0) {
- object_unref(OBJECT(server_ioc));
- error_report_err(local_err);
- return 1;
- }
-
if (device) {
int ret;
--
2.10.2
On 04/02/2017 11:03, Richard W.M. Jones wrote:
> Socket activation (sometimes known as systemd socket activation)
> allows an Internet superserver to pass a pre-opened listening socket
> to the process, instead of having qemu-nbd open a socket itself. This
> is done via the LISTEN_FDS and LISTEN_PID environment variables, and a
> standard file descriptor range.
>
> This change partially implements socket activation for qemu-nbd. If
> the environment variables are set correctly, then socket activation
> will happen automatically, otherwise everything works as before. The
> limitation is that LISTEN_FDS must be 1.
>
> Signed-off-by: Richard W.M. Jones.
> ---
> qemu-nbd.c | 172 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 163 insertions(+), 9 deletions(-)
>
> diff --git a/qemu-nbd.c b/qemu-nbd.c
> index c734f62..e4fede6 100644
> --- a/qemu-nbd.c
> +++ b/qemu-nbd.c
> @@ -463,6 +463,135 @@ static QCryptoTLSCreds *nbd_get_tls_creds(const char *id, Error **errp)
> return creds;
> }
>
> +static void setup_address_and_port(const char **address, const char **port)
> +{
> + if (*address == NULL) {
> + *address = "0.0.0.0";
> + }
> +
> + if (*port == NULL) {
> + *port = stringify(NBD_DEFAULT_PORT);
> + }
> +}
> +
> +#define FIRST_SOCKET_ACTIVATION_FD 3 /* defined by systemd ABI */
> +
> +#ifndef _WIN32
> +/*
> + * Check if socket activation was requested via use of the
> + * LISTEN_FDS and LISTEN_PID environment variables.
> + *
> + * Returns 0 if no socket activation, or the number of FDs.
> + */
> +static unsigned int check_socket_activation(void)
> +{
> + const char *s;
> + unsigned long pid;
> + unsigned long nr_fds;
> + unsigned int i;
> + int fd;
> + int err;
> +
> + s = getenv("LISTEN_PID");
> + if (s == NULL) {
> + return 0;
> + }
> + err = qemu_strtoul(s, NULL, 10, &pid);
> + if (err) {
> + if (verbose) {
> + fprintf(stderr, "malformed %s environment variable (ignored)\n",
> + "LISTEN_PID");
> + }
> + return 0;
> + }
> + if (pid != getpid()) {
> + if (verbose) {
> + fprintf(stderr, "%s was not for us (ignored)\n",
> + "LISTEN_PID");
> + }
> + return 0;
> + }
> +
> + s = getenv("LISTEN_FDS");
> + if (s == NULL) {
> + return 0;
> + }
> + err = qemu_strtoul(s, NULL, 10, &nr_fds);
> + if (err) {
> + if (verbose) {
> + fprintf(stderr, "malformed %s environment variable (ignored)\n",
> + "LISTEN_FDS");
> + }
> + return 0;
> + }
> + assert(nr_fds <= UINT_MAX);
> +
> + /* A limitation of current qemu-nbd is that it can only listen on
> + * a single socket. When that limitation is lifted, we can change
> + * this function to allow LISTEN_FDS > 1, and remove the assertion
> + * in the main function below.
> + */
> + if (nr_fds > 1) {
> + error_report("qemu-nbd does not support socket activation with %s > 1",
> + "LISTEN_FDS");
> + exit(EXIT_FAILURE);
> + }
> +
> + /* So these are not passed to any child processes we might start. */
> + unsetenv("LISTEN_FDS");
> + unsetenv("LISTEN_PID");
> +
> + /* So the file descriptors don't leak into child processes. */
> + for (i = 0; i < nr_fds; ++i) {
> + fd = FIRST_SOCKET_ACTIVATION_FD + i;
> + if (fcntl(fd, F_SETFD, FD_CLOEXEC) == -1) {
> + /* If we cannot set FD_CLOEXEC then it probably means the file
> + * descriptor is invalid, so socket activation has gone wrong
> + * and we should exit.
> + */
> + error_report("Socket activation failed: "
> + "invalid file descriptor fd = %d: %m",
> + fd);
> + exit(EXIT_FAILURE);
> + }
> + }
> +
> + return (unsigned int) nr_fds;
> +}
> +
> +#else /* !_WIN32 */
> +static unsigned int check_socket_activation(void)
> +{
> + return 0;
> +}
> +#endif
> +
> +/*
> + * Check socket parameters compatibility when socket activation is used.
> + */
> +static const char *socket_activation_validate_opts(const char *device,
> + const char *sockpath,
> + const char *address,
> + const char *port)
> +{
> + if (device != NULL) {
> + return "NBD device can't be set when using socket activation";
> + }
> +
> + if (sockpath != NULL) {
> + return "Unix socket can't be set when using socket activation";
> + }
> +
> + if (address != NULL) {
> + return "The interface can't be set when using socket activation";
> + }
> +
> + if (port != NULL) {
> + return "TCP port number can't be set when using socket activation";
> + }
> +
> + return NULL;
> +}
>
> int main(int argc, char **argv)
> {
> @@ -471,7 +600,7 @@ int main(int argc, char **argv)
> off_t dev_offset = 0;
> uint16_t nbdflags = 0;
> bool disconnect = false;
> - const char *bindto = "0.0.0.0";
> + const char *bindto = NULL;
> const char *port = NULL;
> char *sockpath = NULL;
> char *device = NULL;
> @@ -533,6 +662,7 @@ int main(int argc, char **argv)
> char *trace_file = NULL;
> bool fork_process = false;
> int old_stderr = -1;
> + unsigned socket_activation;
>
> /* The client thread uses SIGTERM to interrupt the server. A signal
> * handler ensures that "qemu-nbd -v -c" exits with a nice status code.
> @@ -751,6 +881,19 @@ int main(int argc, char **argv)
> trace_init_file(trace_file);
> qemu_set_log(LOG_TRACE);
>
> + socket_activation = check_socket_activation();
> + if (socket_activation == 0) {
> + setup_address_and_port(&bindto, &port);
> + } else {
> + /* Using socket activation - check user didn't use -p etc. */
> + const char *err_msg = socket_activation_validate_opts(device, sockpath,
> + bindto, port);
> + if (err_msg != NULL) {
> + error_report("%s", err_msg);
> + exit(EXIT_FAILURE);
> + }
> + }
> +
> if (tlscredsid) {
> if (sockpath) {
> error_report("TLS is only supported with IPv4/IPv6");
> @@ -855,7 +998,25 @@ int main(int argc, char **argv)
> snprintf(sockpath, 128, SOCKET_PATH, basename(device));
> }
>
> - saddr = nbd_build_socket_address(sockpath, bindto, port);
> + if (socket_activation == 0) {
> + server_ioc = qio_channel_socket_new();
> + saddr = nbd_build_socket_address(sockpath, bindto, port);
> + if (qio_channel_socket_listen_sync(server_ioc, saddr, &local_err) < 0) {
> + object_unref(OBJECT(server_ioc));
> + error_report_err(local_err);
> + return 1;
> + }
> + } else {
> + /* See comment in check_socket_activation above. */
> + assert(socket_activation == 1);
> + server_ioc = qio_channel_socket_new_fd(FIRST_SOCKET_ACTIVATION_FD,
> + &local_err);
> + if (server_ioc == NULL) {
> + error_report("Failed to use socket activation: %s",
> + error_get_pretty(local_err));
> + exit(EXIT_FAILURE);
> + }
> + }
>
> if (qemu_init_main_loop(&local_err)) {
> error_report_err(local_err);
> @@ -950,13 +1111,6 @@ int main(int argc, char **argv)
> exit(EXIT_FAILURE);
> }
>
> - server_ioc = qio_channel_socket_new();
> - if (qio_channel_socket_listen_sync(server_ioc, saddr, &local_err) < 0) {
> - object_unref(OBJECT(server_ioc));
> - error_report_err(local_err);
> - return 1;
> - }
> -
> if (device) {
> int ret;
>
>
Queued, thanks.
Paolo
On Mon, Feb 06, 2017 at 05:10:13PM +0100, Paolo Bonzini wrote:
> Queued, thanks.
Could you change this comment s/!_WIN32/_WIN32/, or do you
want me to submit another patch?
> > +#else /* !_WIN32 */
> > +static unsigned int check_socket_activation(void)
> > +{
> > + return 0;
> > +}
> > +#endif
> > +
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
libguestfs lets you edit virtual machines. Supports shell scripting,
bindings from many languages. http://libguestfs.org
On 06/02/2017 17:29, Richard W.M. Jones wrote:
> On Mon, Feb 06, 2017 at 05:10:13PM +0100, Paolo Bonzini wrote:
>> Queued, thanks.
>
> Could you change this comment s/!_WIN32/_WIN32/, or do you
> want me to submit another patch?
>
>>> +#else /* !_WIN32 */
>>> +static unsigned int check_socket_activation(void)
>>> +{
>>> + return 0;
>>> +}
>>> +#endif
>>> +
>
> Rich.
>
Will do, and use CONFIG_WIN32 while at it.
Paolo
On 02/04/2017 04:03 AM, Richard W.M. Jones wrote:
> Socket activation (sometimes known as systemd socket activation)
> allows an Internet superserver to pass a pre-opened listening socket
> to the process, instead of having qemu-nbd open a socket itself. This
> is done via the LISTEN_FDS and LISTEN_PID environment variables, and a
> standard file descriptor range.
>
> This change partially implements socket activation for qemu-nbd. If
> the environment variables are set correctly, then socket activation
> will happen automatically, otherwise everything works as before. The
> limitation is that LISTEN_FDS must be 1.
>
> Signed-off-by: Richard W.M. Jones.
> ---
> +
> + /* So the file descriptors don't leak into child processes. */
> + for (i = 0; i < nr_fds; ++i) {
> + fd = FIRST_SOCKET_ACTIVATION_FD + i;
> + if (fcntl(fd, F_SETFD, FD_CLOEXEC) == -1) {
This is not the right way to do things (it risks clearing any other FD_
flags currently set on the fd, even though there aren't any such FD_
flags in common use). You HAVE to do F_GETFD before F_SETFD
(read-modify-write) for correct usage - and the best way to do that is
to use qemu_set_cloexec() from util/oslib-posix.c.
Except that qemu_set_cloexec() doesn't pay attention to errors...
> + /* If we cannot set FD_CLOEXEC then it probably means the file
> + * descriptor is invalid, so socket activation has gone wrong
> + * and we should exit.
> + */
> + error_report("Socket activation failed: "
> + "invalid file descriptor fd = %d: %m",
> + fd);
...while you use it for argument validation. Hmm.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
On 06/02/2017 20:04, Eric Blake wrote: > This is not the right way to do things (it risks clearing any other FD_ > flags currently set on the fd, even though there aren't any such FD_ > flags in common use). There aren't any such flags at all really, and because no one uses F_GETFD, it's unlikely that there will ever be any. Has any other POSIX OS ever had one? Paolo
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