* [Qemu-devel] [PATCH] qemu-nbd: Implement socket activation. @ 2017-02-02 14:51 Richard W.M. Jones 2017-02-02 14:51 ` Richard W.M. Jones 0 siblings, 1 reply; 3+ messages in thread From: Richard W.M. Jones @ 2017-02-02 14:51 UTC (permalink / raw) To: pbonzini; +Cc: qemu-devel, den, rkagan, dplotnikov, berrange, stefanha 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 patch partially implements socket activation. The limitation of this implementation is that qemu-nbd can only listen on a single file descriptor, and so if LISTEN_FDS > 1 (eg. for listening on multiple interfaces or ports) socket activation will fail. However for the simple case of listening on a single port, and either all interfaces with IPv4+IPv6, or just a loopback interface, the current implementation works fine. Fixing this properly would require considerable changes throughout qemu, since qemu's currently handling of getaddrinfo is plainly wrong. To use qemu-nbd from systemd, you create /etc/systemd/system/nbd.socket: [Unit] Description=QEMU Network Block Device server [Socket] ListenStream=10809 [Install] WantedBy=sockets.target and /etc/systemd/system/nbd.service: [Service] ExecStart=/usr/sbin/qemu-nbd -v -t /path/to/file and enable the socket service (only): systemctl enable nbd.socket systemctl start nbd.socket and then connecting to port 10809 will start qemu-nbd and service the file, with systemd opening the listening socket. In the ExecStart line, the qemu-nbd -v option is only needed if you want enhanced debugging. The -t option is required unless you want to fiddle with systemd settings for rate-limiting. If you try to use the -p and similar options with socket activation then qemu-nbd will give an error. (I wasn't sure where to document this -- there is no obvious documentation for qemu-nbd beyond the simple list of command line arguments) This is based on the implementations in libvirt (src/util/virutil.c:virGetListenFDs) and nbdkit (src/main.c:get_socket_activation), and also on Denis Plotnikov's implementation of --server-sock-fd (https://lists.gnu.org/archive/html/qemu-devel/2016-09/msg07781.html). Rich. ^ permalink raw reply [flat|nested] 3+ messages in thread
* [Qemu-devel] [PATCH] qemu-nbd: Implement socket activation. 2017-02-02 14:51 [Qemu-devel] [PATCH] qemu-nbd: Implement socket activation Richard W.M. Jones @ 2017-02-02 14:51 ` Richard W.M. Jones 2017-02-02 15:04 ` Daniel P. Berrange 0 siblings, 1 reply; 3+ messages in thread From: Richard W.M. Jones @ 2017-02-02 14:51 UTC (permalink / raw) To: pbonzini; +Cc: qemu-devel, den, rkagan, dplotnikov, berrange, stefanha 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 | 174 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 162 insertions(+), 12 deletions(-) diff --git a/qemu-nbd.c b/qemu-nbd.c index c734f62..bfa52c3 100644 --- a/qemu-nbd.c +++ b/qemu-nbd.c @@ -386,9 +386,9 @@ static void nbd_update_server_watch(void) } -static SocketAddress *nbd_build_socket_address(const char *sockpath, - const char *bindto, - const char *port) +static SocketAddress *nbd_build_socket_fd(const char *sockpath, + const char *bindto, + const char *port) { SocketAddress *saddr; @@ -463,6 +463,131 @@ 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 = g_strdup_printf("%d", 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 int pid; + unsigned int nr_fds; + unsigned int i; + int fd; + + s = getenv("LISTEN_PID"); + if (s == NULL) { + return 0; + } + if (sscanf(s, "%u", &pid) != 1) { + 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; + } + if (sscanf(s, "%u", &nr_fds) != 1) { + if (verbose) { + fprintf(stderr, "malformed %s environment variable (ignored)\n", + "LISTEN_FDS"); + } + return 0; + } + + /* 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 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 +596,7 @@ 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 +658,7 @@ 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 +877,19 @@ 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 +994,25 @@ 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_fd(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 +1107,6 @@ 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 ^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [Qemu-devel] [PATCH] qemu-nbd: Implement socket activation. 2017-02-02 14:51 ` Richard W.M. Jones @ 2017-02-02 15:04 ` Daniel P. Berrange 0 siblings, 0 replies; 3+ messages in thread From: Daniel P. Berrange @ 2017-02-02 15:04 UTC (permalink / raw) To: Richard W.M. Jones Cc: pbonzini, qemu-devel, den, rkagan, dplotnikov, stefanha On Thu, Feb 02, 2017 at 02:51:59PM +0000, 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 | 174 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++----- > 1 file changed, 162 insertions(+), 12 deletions(-) > > diff --git a/qemu-nbd.c b/qemu-nbd.c > index c734f62..bfa52c3 100644 > --- a/qemu-nbd.c > +++ b/qemu-nbd.c > @@ -386,9 +386,9 @@ static void nbd_update_server_watch(void) > } > > > -static SocketAddress *nbd_build_socket_address(const char *sockpath, > - const char *bindto, > - const char *port) > +static SocketAddress *nbd_build_socket_fd(const char *sockpath, > + const char *bindto, > + const char *port) I don't think this needs renaming - its still returning an address rather than an FD > { > SocketAddress *saddr; > > @@ -463,6 +463,131 @@ 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 = g_strdup_printf("%d", 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 int pid; > + unsigned int nr_fds; > + unsigned int i; > + int fd; > + > + s = getenv("LISTEN_PID"); > + if (s == NULL) { > + return 0; > + } > + if (sscanf(s, "%u", &pid) != 1) { IIRC qemu_strtoul would be preferred for this. > + 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; > + } > + if (sscanf(s, "%u", &nr_fds) != 1) { And this. > + if (verbose) { > + fprintf(stderr, "malformed %s environment variable (ignored)\n", > + "LISTEN_FDS"); > + } > + return 0; > + } > + > + /* 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 nr_fds; > +} > + > +#else /* !_WIN32 */ > +static unsigned int check_socket_activation(void) > +{ > + return 0; > +} > +#endif Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :| ^ permalink raw reply [flat|nested] 3+ messages in thread
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