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qemu-nbd: Implement socket activation.

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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 <rjones@redhat.com>
Message-Id: <20170204100317.32425-2-rjones@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Richard W.M. Jones 2017-02-04 10:03:17 +00:00 committed by Paolo Bonzini
parent 41eeb0e601
commit a721f53b8f
1 changed files with 163 additions and 9 deletions
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172
qemu-nbd.c
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@ -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;