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

[Darrin M. Gorski]

>> Yes, but they can override the default behaviour, or just reuse some code.

>> If it doesn't fit, don't worry about it, we can just start with socket.

Whew.  I spent several hours yesterday trying to figure out how to alter the base class to support this - DCD could be reasonably simple, but DTR is another matter.  I will continue to look at that, but I do think moving forward with sockets (since this patch already works that way) is a good compromise.

> You can look at char_socket_server_test.

Will do.

- Darrin

On Fri, Dec 18, 2020 at 6:57 AM Marc-André Lureau <marcandre.lureau@gmail.com> wrote:

Hi

On Thu, Dec 17, 2020 at 9:54 PM Darrin M. Gorski <darrin@gorski.net> wrote:

> That sounds like a good idea to me, but others may have different opinions.

My original idea was simply to allow DCD to track socket state, because this is what I need.  The DTR idea came from the referenced bug.  The feature defaults to disabled like many of the other edge cases (like telnet and tn3270), and it's a reasonably small non-intrusive change.

> Can we make this generic over all chardevs by moving it to the base class?

I'll take a closer look at the base class. I admit I did not spend much time studying it.  This seemed like a socket specific feature to me.  It seems like it might conflict with other chardevs like pty and serial as they are already using ioctl for interaction with real tty devices.

Yes, but they can override the default behaviour, or just reuse some code.

If it doesn't fit, don't worry about it, we can just start with socket.

 

> This feature will need some new tests in tests/test-char.c.

I would be happy to add tests but would need some guidance.

You can look at char_socket_server_test. You can extend CharSocketServerTestConfig to check for modemctl behaviour. It will need to send the ioctl with qemu_chr_fe_ioctl (I admit it wasn't tested so far, because only serial and parallel chardev did implement it, and it's not easy to test those)

Let me know if you need more help

 

- Darrin

On Thu, Dec 17, 2020 at 9:16 AM Marc-André Lureau <marcandre.lureau@gmail.com> wrote:

Hi

On Thu, Dec 17, 2020 at 2:54 AM Darrin M. Gorski <darrin@gorski.net> wrote:

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

That sounds like a good idea to me, but others may have different opinions.

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;

Can we make this generic over all chardevs by moving it to the base class?

 };
 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"

This feature will need some new tests in tests/test-char.c.

--

Marc-André Lureau

--

Marc-André Lureau