[PATCH v1 1/1] chardev: enable guest socket status/crontrol via DTR and DCD

["Darrin M. Gorski" <darrin@gorski.net>]

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This patch adds a 'modemctl' option to "-chardev socket" to enable control
of the socket via the guest serial port.
The default state of the option is disabled.

1. disconnect a connected socket when DTR transitions to low, also reject
new connections while DTR is low.
2. provide socket connection status through the carrier detect line (CD or
DCD) on the guest serial port

Buglink: https://bugs.launchpad.net/qemu/+bug/1213196

Signed-off-by: Darrin M. Gorski <darrin@gorski.net>


diff --git a/chardev/char-socket.c b/chardev/char-socket.c
index 213a4c8dd0..94dd28e0cd 100644
--- a/chardev/char-socket.c
+++ b/chardev/char-socket.c
@@ -36,6 +36,7 @@
 #include "qapi/qapi-visit-sockets.h"

 #include "chardev/char-io.h"
+#include "chardev/char-serial.h"
 #include "qom/object.h"

 /***********************************************************/
@@ -85,6 +86,9 @@ struct SocketChardev {
     bool connect_err_reported;

     QIOTask *connect_task;
+
+    bool is_modemctl;
+    int modem_state;
 };
 typedef struct SocketChardev SocketChardev;

@@ -98,12 +102,18 @@ static void tcp_chr_change_state(SocketChardev *s,
TCPChardevState state)
 {
     switch (state) {
     case TCP_CHARDEV_STATE_DISCONNECTED:
+        if(s->is_modemctl) {
+            s->modem_state &= ~(CHR_TIOCM_CAR);
+        }
         break;
     case TCP_CHARDEV_STATE_CONNECTING:
         assert(s->state == TCP_CHARDEV_STATE_DISCONNECTED);
         break;
     case TCP_CHARDEV_STATE_CONNECTED:
         assert(s->state == TCP_CHARDEV_STATE_CONNECTING);
+        if(s->is_modemctl) {
+            s->modem_state |= CHR_TIOCM_CAR;
+        }
         break;
     }
     s->state = state;
@@ -947,6 +957,12 @@ static void tcp_chr_accept(QIONetListener *listener,
     tcp_chr_change_state(s, TCP_CHARDEV_STATE_CONNECTING);
     tcp_chr_set_client_ioc_name(chr, cioc);
     tcp_chr_new_client(chr, cioc);
+
+    if(s->is_modemctl) {
+        if(!(s->modem_state & CHR_TIOCM_DTR)) {
+            tcp_chr_disconnect(chr); /* disconnect if DTR is low */
+        }
+    }
 }


@@ -1322,12 +1338,17 @@ static void qmp_chardev_open_socket(Chardev *chr,
     bool is_tn3270      = sock->has_tn3270  ? sock->tn3270  : false;
     bool is_waitconnect = sock->has_wait    ? sock->wait    : false;
     bool is_websock     = sock->has_websocket ? sock->websocket : false;
+    bool is_modemctl     = sock->has_modemctl ? sock->modemctl : false;
     int64_t reconnect   = sock->has_reconnect ? sock->reconnect : 0;
     SocketAddress *addr;

     s->is_listen = is_listen;
     s->is_telnet = is_telnet;
     s->is_tn3270 = is_tn3270;
+    s->is_modemctl = is_modemctl;
+    if(is_modemctl) {
+      s->modem_state = CHR_TIOCM_CTS | CHR_TIOCM_DSR;
+    }
     s->is_websock = is_websock;
     s->do_nodelay = do_nodelay;
     if (sock->tls_creds) {
@@ -1448,6 +1469,8 @@ static void qemu_chr_parse_socket(QemuOpts *opts,
ChardevBackend *backend,
     sock->tls_creds = g_strdup(qemu_opt_get(opts, "tls-creds"));
     sock->has_tls_authz = qemu_opt_get(opts, "tls-authz");
     sock->tls_authz = g_strdup(qemu_opt_get(opts, "tls-authz"));
+    sock->has_modemctl = qemu_opt_get(opts, "modemctl");
+    sock->modemctl = qemu_opt_get_bool(opts, "modemctl", false);

     addr = g_new0(SocketAddressLegacy, 1);
     if (path) {
@@ -1501,6 +1524,51 @@ char_socket_get_connected(Object *obj, Error **errp)
     return s->state == TCP_CHARDEV_STATE_CONNECTED;
 }

+/* ioctl support: allow guest to control/track socket state
+ * via modem control lines (DCD/DTR)
+ */
+static int
+char_socket_ioctl(Chardev *chr, int cmd, void *arg)
+{
+    SocketChardev *s = SOCKET_CHARDEV(chr);
+
+    if(!(s->is_modemctl)) {
+        return -ENOTSUP;
+    }
+
+    switch (cmd) {
+        case CHR_IOCTL_SERIAL_GET_TIOCM:
+            {
+                int *targ = (int *)arg;
+                *targ = s->modem_state;
+            }
+            break;
+        case CHR_IOCTL_SERIAL_SET_TIOCM:
+            {
+                int sarg = *(int *)arg;
+                if (sarg & CHR_TIOCM_RTS) {
+                    s->modem_state |= CHR_TIOCM_RTS;
+                } else {
+                    s->modem_state &= ~(CHR_TIOCM_RTS);
+                }
+                if (sarg & CHR_TIOCM_DTR) {
+                    s->modem_state |= CHR_TIOCM_DTR;
+                } else {
+                    s->modem_state &= ~(CHR_TIOCM_DTR);
+                    /* disconnect if DTR goes low */
+                    if(s->state == TCP_CHARDEV_STATE_CONNECTED) {
+                        tcp_chr_disconnect(chr);
+                    }
+                }
+            }
+            break;
+        default:
+            return -ENOTSUP;
+    }
+
+    return 0;
+}
+
 static void char_socket_class_init(ObjectClass *oc, void *data)
 {
     ChardevClass *cc = CHARDEV_CLASS(oc);
@@ -1516,6 +1584,7 @@ static void char_socket_class_init(ObjectClass *oc,
void *data)
     cc->chr_add_client = tcp_chr_add_client;
     cc->chr_add_watch = tcp_chr_add_watch;
     cc->chr_update_read_handler = tcp_chr_update_read_handler;
+    cc->chr_ioctl = char_socket_ioctl;

     object_class_property_add(oc, "addr", "SocketAddress",
                               char_socket_get_addr, NULL,
diff --git a/chardev/char.c b/chardev/char.c
index a9b8c5a9aa..601d818f81 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -928,6 +928,9 @@ QemuOptsList qemu_chardev_opts = {
         },{
             .name = "logappend",
             .type = QEMU_OPT_BOOL,
+        },{
+            .name = "modemctl",
+            .type = QEMU_OPT_BOOL,
 #ifdef CONFIG_LINUX
         },{
             .name = "tight",
diff --git a/qapi/char.json b/qapi/char.json
index 58338ed62d..f352bd6350 100644
--- a/qapi/char.json
+++ b/qapi/char.json
@@ -271,6 +271,9 @@
 #             then attempt a reconnect after the given number of seconds.
 #             Setting this to zero disables this function. (default: 0)
 #             (Since: 2.2)
+# @modemctl: allow guest to use modem control signals to control/monitor
+#            the socket state (CD follows is_connected, DTR influences
+#            connect/accept) (default: false) (Since: 5.2)
 #
 # Since: 1.4
 ##
@@ -284,6 +287,7 @@
             '*telnet': 'bool',
             '*tn3270': 'bool',
             '*websocket': 'bool',
+            '*modemctl': 'bool',
             '*reconnect': 'int' },
   'base': 'ChardevCommon' }

diff --git a/qemu-options.hx b/qemu-options.hx
index 459c916d3d..f09072afbf 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -2991,11 +2991,13 @@ DEFHEADING(Character device options:)
 DEF("chardev", HAS_ARG, QEMU_OPTION_chardev,
     "-chardev help\n"
     "-chardev null,id=id[,mux=on|off][,logfile=PATH][,logappend=on|off]\n"
-    "-chardev
socket,id=id[,host=host],port=port[,to=to][,ipv4][,ipv6][,nodelay][,reconnect=seconds]\n"
-    "
[,server][,nowait][,telnet][,websocket][,reconnect=seconds][,mux=on|off]\n"
-    "
[,logfile=PATH][,logappend=on|off][,tls-creds=ID][,tls-authz=ID] (tcp)\n"
-    "-chardev
socket,id=id,path=path[,server][,nowait][,telnet][,websocket][,reconnect=seconds]\n"
-    "
[,mux=on|off][,logfile=PATH][,logappend=on|off][,abstract=on|off][,tight=on|off]
(unix)\n"
+    "-chardev
socket,id=id[,host=host],port=port[,to=to][,ipv4][,ipv6][,nodelay]\n"
+    "
[,reconnect=seconds][,server][,nowait][,telnet][,websocket]\n"
+    "         [,modemctl][,mux=on|off][,logfile=PATH][,logappend=on|off]\n"
+    "         [,tls-creds=ID][,tls-authz=ID] (tcp)\n"
+    "-chardev
socket,id=id,path=path[,server][,nowait][,telnet][,websocket]\n"
+    "
[,reconnect=seconds][,modemctl][,mux=on|off][,logfile=PATH]\n"
+    "         [,logappend=on|off][,abstract=on|off][,tight=on|off]
(unix)\n"
     "-chardev udp,id=id[,host=host],port=port[,localaddr=localaddr]\n"
     "         [,localport=localport][,ipv4][,ipv6][,mux=on|off]\n"
     "         [,logfile=PATH][,logappend=on|off]\n"

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