Introduce a 'client_add' monitor command accepting an open FD

Allow client connections for VNC and socket based character
devices to be passed in over the monitor using SCM_RIGHTS.

One intended usage scenario is to start QEMU with VNC on a
UNIX domain socket. An unprivileged user which cannot access
the UNIX domain socket, can then connect to QEMU's VNC server
by passing an open FD to libvirt, which passes it onto QEMU.

 { "execute": "get_fd", "arguments": { "fdname": "myclient" } }
 { "return": {} }
 { "execute": "add_client", "arguments": { "protocol": "vnc",
                                           "fdname": "myclient",
                                           "skipauth": true } }
 { "return": {} }

In this case 'protocol' can be 'vnc' or 'spice', or the name
of a character device (eg from -chardev id=XXXX)

The 'skipauth' parameter can be used to skip any configured
VNC authentication scheme, which is useful if the mgmt layer
talking to the monitor has already authenticated the client
in another way.

* console.h: Define 'vnc_display_add_client' method
* monitor.c: Implement 'client_add' command
* qemu-char.c, qemu-char.h: Add 'qemu_char_add_client' method
* qerror.c, qerror.h: Add QERR_ADD_CLIENT_FAILED
* qmp-commands.hx: Declare 'client_add' command
* ui/vnc.c: Implement 'vnc_display_add_client' method

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

console.h

@@ -372,6 +372,7 @@ void cocoa_display_init(DisplayState *ds, int full_screen);
 void vnc_display_init(DisplayState *ds);
 void vnc_display_close(DisplayState *ds);
 int vnc_display_open(DisplayState *ds, const char *display);
+void vnc_display_add_client(DisplayState *ds, int csock, int skipauth);
 int vnc_display_disable_login(DisplayState *ds);
 char *vnc_display_local_addr(DisplayState *ds);
 #ifdef CONFIG_VNC

monitor.c

@@ -1185,6 +1185,38 @@ static int expire_password(Monitor *mon, const QDict *qdict, QObject **ret_data)
     return -1;
 }
 
+static int add_graphics_client(Monitor *mon, const QDict *qdict, QObject **ret_data)
+{
+    const char *protocol  = qdict_get_str(qdict, "protocol");
+    const char *fdname = qdict_get_str(qdict, "fdname");
+    int skipauth = qdict_get_try_bool(qdict, "skipauth", 0);
+    CharDriverState *s;
+
+    if (strcmp(protocol, "spice") == 0) {
+        if (!using_spice) {
+            /* correct one? spice isn't a device ,,, */
+            qerror_report(QERR_DEVICE_NOT_ACTIVE, "spice");
+            return -1;
+        }
+	qerror_report(QERR_ADD_CLIENT_FAILED);
+	return -1;
+    } else if (strcmp(protocol, "vnc") == 0) {
+	int fd = monitor_get_fd(mon, fdname);
+	vnc_display_add_client(NULL, fd, skipauth);
+	return 0;
+    } else if ((s = qemu_chr_find(protocol)) != NULL) {
+	int fd = monitor_get_fd(mon, fdname);
+	if (qemu_chr_add_client(s, fd) < 0) {
+	    qerror_report(QERR_ADD_CLIENT_FAILED);
+	    return -1;
+	}
+	return 0;
+    }
+
+    qerror_report(QERR_INVALID_PARAMETER, "protocol");
+    return -1;
+}
+
 static int client_migrate_info(Monitor *mon, const QDict *qdict, QObject **ret_data)
 {
     const char *protocol = qdict_get_str(qdict, "protocol");

qemu-char.c

@@ -168,6 +168,11 @@ int qemu_chr_get_msgfd(CharDriverState *s)
     return s->get_msgfd ? s->get_msgfd(s) : -1;
 }
 
+int qemu_chr_add_client(CharDriverState *s, int fd)
+{
+    return s->chr_add_client ? s->chr_add_client(s, fd) : -1;
+}
+
 void qemu_chr_accept_input(CharDriverState *s)
 {
     if (s->chr_accept_input)
@@ -2146,6 +2151,22 @@ static void socket_set_nodelay(int fd)
     setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, (char *)&val, sizeof(val));
 }
 
+static int tcp_chr_add_client(CharDriverState *chr, int fd)
+{
+    TCPCharDriver *s = chr->opaque;
+    if (s->fd != -1)
+	return -1;
+
+    socket_set_nonblock(fd);
+    if (s->do_nodelay)
+        socket_set_nodelay(fd);
+    s->fd = fd;
+    qemu_set_fd_handler(s->listen_fd, NULL, NULL, NULL);
+    tcp_chr_connect(chr);
+
+    return 0;
+}
+
 static void tcp_chr_accept(void *opaque)
 {
     CharDriverState *chr = opaque;
@@ -2178,12 +2199,8 @@ static void tcp_chr_accept(void *opaque)
             break;
         }
     }
-    socket_set_nonblock(fd);
-    if (s->do_nodelay)
-        socket_set_nodelay(fd);
-    s->fd = fd;
-    qemu_set_fd_handler(s->listen_fd, NULL, NULL, NULL);
-    tcp_chr_connect(chr);
+    if (tcp_chr_add_client(chr, fd) < 0)
+	close(fd);
 }
 
 static void tcp_chr_close(CharDriverState *chr)
@@ -2256,6 +2273,7 @@ static int qemu_chr_open_socket(QemuOpts *opts, CharDriverState **_chr)
     chr->chr_write = tcp_chr_write;
     chr->chr_close = tcp_chr_close;
     chr->get_msgfd = tcp_get_msgfd;
+    chr->chr_add_client = tcp_chr_add_client;
 
     if (is_listen) {
         s->listen_fd = fd;

qemu-char.h

@@ -57,6 +57,7 @@ struct CharDriverState {
     void (*chr_update_read_handler)(struct CharDriverState *s);
     int (*chr_ioctl)(struct CharDriverState *s, int cmd, void *arg);
     int (*get_msgfd)(struct CharDriverState *s);
+    int (*chr_add_client)(struct CharDriverState *chr, int fd);
     IOEventHandler *chr_event;
     IOCanReadHandler *chr_can_read;
     IOReadHandler *chr_read;
@@ -99,6 +100,7 @@ int qemu_chr_can_read(CharDriverState *s);
 void qemu_chr_read(CharDriverState *s, uint8_t *buf, int len);
 int qemu_chr_get_msgfd(CharDriverState *s);
 void qemu_chr_accept_input(CharDriverState *s);
+int qemu_chr_add_client(CharDriverState *s, int fd);
 void qemu_chr_info_print(Monitor *mon, const QObject *ret_data);
 void qemu_chr_info(Monitor *mon, QObject **ret_data);
 CharDriverState *qemu_chr_find(const char *name);

qerror.c

@@ -197,6 +197,10 @@ static const QErrorStringTable qerror_table[] = {
         .error_fmt = QERR_SET_PASSWD_FAILED,
         .desc      = "Could not set password",
     },
+    {
+        .error_fmt = QERR_ADD_CLIENT_FAILED,
+        .desc      = "Could not add client",
+    },
     {
         .error_fmt = QERR_TOO_MANY_FILES,
         .desc      = "Too many open files",

qerror.h

@@ -166,6 +166,9 @@ QError *qobject_to_qerror(const QObject *obj);
 #define QERR_SET_PASSWD_FAILED \
     "{ 'class': 'SetPasswdFailed', 'data': {} }"
 
+#define QERR_ADD_CLIENT_FAILED \
+    "{ 'class': 'AddClientFailed', 'data': {} }"
+
 #define QERR_TOO_MANY_FILES \
     "{ 'class': 'TooManyFiles', 'data': {} }"
 

qmp-commands.hx

@@ -918,6 +918,33 @@ Example:
 
 EQMP
 
+    {
+        .name       = "add_client",
+        .args_type  = "protocol:s,fdname:s,skipauth:b?",
+        .params     = "protocol fdname skipauth",
+        .help       = "add a graphics client",
+        .user_print = monitor_user_noop,
+        .mhandler.cmd_new = add_graphics_client,
+    },
+
+SQMP
+add_client
+----------
+
+Add a graphics client
+
+Arguments:
+
+- "protocol": protocol name (json-string)
+- "fdname": file descriptor name (json-string)
+
+Example:
+
+-> { "execute": "add_client", "arguments": { "protocol": "vnc",
+                                             "fdname": "myclient" } }
+<- { "return": {} }
+
+EQMP
     {
         .name       = "qmp_capabilities",
         .args_type  = "",

ui/vnc.c

@@ -2924,3 +2924,10 @@ int vnc_display_open(DisplayState *ds, const char *display)
     }
     return qemu_set_fd_handler2(vs->lsock, NULL, vnc_listen_read, NULL, vs);
 }
+
+void vnc_display_add_client(DisplayState *ds, int csock, int skipauth)
+{
+    VncDisplay *vs = ds ? (VncDisplay *)ds->opaque : vnc_display;
+
+    return vnc_connect(vs, csock, skipauth);
+}