From 55c9510311b7481a0c8f3f71b3ce130cc25563f9 Mon Sep 17 00:00:00 2001
From: Alistair Francis <alistair.francis@xilinx.com>
Date: Thu, 21 Dec 2017 11:35:16 -0800
Subject: [PATCH] chardev: connect socket to a spawned command

The command is started in a shell (sh -c) with stdin connect to QEMU
via a Unix domain stream socket. QEMU then exchanges data via its own
end of the socket, just like it normally does.

"-chardev socket" supports some ways of connecting via protocols like
telnet, but that is only a subset of the functionality supported by
tools socat. To use socat instead, for example to connect via a socks
proxy, use:

  -chardev 'socket,id=socat,cmd=exec socat FD:0 SOCKS4A:socks-proxy.localdomain:example.com:9999,,socksuser=nobody' \
  -device usb-serial,chardev=socat

Beware that commas in the command must be escaped as double commas.

Or interactively in the console:
   (qemu) chardev-add socket,id=cat,cmd=cat
   (qemu) device_add usb-serial,chardev=cat
   ^ac
   # cat >/dev/ttyUSB0
   hello
   hello

Another usage is starting swtpm from inside QEMU. swtpm will
automatically shut down once it looses the connection to the parent
QEMU, so there is no risk of lingering processes:

  -chardev 'socket,id=chrtpm0,cmd=exec swtpm socket --terminate --ctrl type=unixio,,clientfd=0 --tpmstate dir=... --log file=swtpm.log' \
  -tpmdev emulator,id=tpm0,chardev=chrtpm0 \
  -device tpm-tis,tpmdev=tpm0

The patch was discussed upstream, but QEMU developers believe that the
code calling QEMU should be responsible for managing additional
processes. In OE-core, that would imply enhancing runqemu and
oeqa. This patch is a simpler solution.

Because it is not going upstream, the patch was written so that it is
as simple as possible.

Upstream-Status: Inappropriate [embedded specific]

Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>
---
 chardev/char-socket.c | 99 +++++++++++++++++++++++++++++++++++++++++++++++++++
 chardev/char.c        |  3 ++
 qapi/char.json        |  5 +++
 3 files changed, 107 insertions(+)

diff --git a/chardev/char-socket.c b/chardev/char-socket.c
index 53eda8e..6c63555 100644
--- a/chardev/char-socket.c
+++ b/chardev/char-socket.c
@@ -852,6 +852,68 @@ static gboolean socket_reconnect_timeout(gpointer opaque)
     return false;
 }
 
+#ifndef _WIN32
+static void chardev_open_socket_cmd(Chardev *chr,
+                                    const char *cmd,
+                                    Error **errp)
+{
+    int fds[2] = { -1, -1 };
+    QIOChannelSocket *sioc = NULL;
+    pid_t pid = -1;
+    const char *argv[] = { "/bin/sh", "-c", cmd, NULL };
+
+    /*
+     * We need a Unix domain socket for commands like swtpm and a single
+     * connection, therefore we cannot use qio_channel_command_new_spawn()
+     * without patching it first. Duplicating the functionality is easier.
+     */
+    if (socketpair(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0, fds)) {
+        error_setg_errno(errp, errno, "Error creating socketpair(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC)");
+        goto error;
+    }
+
+    pid = qemu_fork(errp);
+    if (pid < 0) {
+        goto error;
+    }
+
+    if (!pid) {
+        /* child */
+        dup2(fds[1], STDIN_FILENO);
+        execv(argv[0], (char * const *)argv);
+        _exit(1);
+    }
+
+    /*
+     * Hand over our end of the socket pair to the qio channel.
+     *
+     * We don't reap the child because it is expected to keep
+     * running. We also don't support the "reconnect" option for the
+     * same reason.
+     */
+    sioc = qio_channel_socket_new_fd(fds[0], errp);
+    if (!sioc) {
+        goto error;
+    }
+    fds[0] = -1;
+
+    g_free(chr->filename);
+    chr->filename = g_strdup_printf("cmd:%s", cmd);
+    tcp_chr_new_client(chr, sioc);
+
+ error:
+    if (fds[0] >= 0) {
+        close(fds[0]);
+    }
+    if (fds[1] >= 0) {
+        close(fds[1]);
+    }
+    if (sioc) {
+        object_unref(OBJECT(sioc));
+    }
+}
+#endif
+
 static void qmp_chardev_open_socket(Chardev *chr,
                                     ChardevBackend *backend,
                                     bool *be_opened,
@@ -859,6 +921,9 @@ static void qmp_chardev_open_socket(Chardev *chr,
 {
     SocketChardev *s = SOCKET_CHARDEV(chr);
     ChardevSocket *sock = backend->u.socket.data;
+#ifndef _WIN32
+    const char *cmd     = sock->cmd;
+#endif
     bool do_nodelay     = sock->has_nodelay ? sock->nodelay : false;
     bool is_listen      = sock->has_server  ? sock->server  : true;
     bool is_telnet      = sock->has_telnet  ? sock->telnet  : false;
@@ -925,7 +990,14 @@ static void qmp_chardev_open_socket(Chardev *chr,
     } else if (reconnect > 0) {
         s->reconnect_time = reconnect;
     }
+#ifndef _WIN32
+    if (cmd) {
+        chardev_open_socket_cmd(chr, cmd, errp);
 
+        /* everything ready (or failed permanently) before we return */
+        *be_opened = true;
+    } else
+#endif
     if (s->reconnect_time) {
         sioc = qio_channel_socket_new();
         tcp_chr_set_client_ioc_name(chr, sioc);
@@ -985,10 +1057,26 @@ static void qemu_chr_parse_socket(QemuOpts *opts, ChardevBackend *backend,
     const char *host = qemu_opt_get(opts, "host");
     const char *port = qemu_opt_get(opts, "port");
     const char *tls_creds = qemu_opt_get(opts, "tls-creds");
+#ifndef _WIN32
+    const char *cmd = qemu_opt_get(opts, "cmd");
+#endif
     SocketAddressLegacy *addr;
     ChardevSocket *sock;
 
     backend->type = CHARDEV_BACKEND_KIND_SOCKET;
+#ifndef _WIN32
+    if (cmd) {
+        /*
+         * Here we have to ensure that no options are set which are incompatible with
+         * spawning a command, otherwise unmodified code that doesn't know about
+         * command spawning (like socket_reconnect_timeout()) might get called.
+         */
+        if (path || is_listen || is_telnet || is_tn3270 || reconnect || host || port || tls_creds) {
+            error_setg(errp, "chardev: socket: cmd does not support any additional options");
+            return;
+        }
+    } else
+#endif
     if (!path) {
         if (!host) {
             error_setg(errp, "chardev: socket: no host given");
@@ -1021,13 +1109,24 @@ static void qemu_chr_parse_socket(QemuOpts *opts, ChardevBackend *backend,
     sock->has_reconnect = true;
     sock->reconnect = reconnect;
     sock->tls_creds = g_strdup(tls_creds);
+#ifndef _WIN32
+    sock->cmd = g_strdup(cmd);
+#endif
 
     addr = g_new0(SocketAddressLegacy, 1);
+#ifndef _WIN32
+    if (path || cmd) {
+#else
     if (path) {
+#endif
         UnixSocketAddress *q_unix;
         addr->type = SOCKET_ADDRESS_LEGACY_KIND_UNIX;
         q_unix = addr->u.q_unix.data = g_new0(UnixSocketAddress, 1);
+#ifndef _WIN32
+        q_unix->path = cmd ? g_strdup_printf("cmd:%s", cmd) : g_strdup(path);
+#else
         q_unix->path = g_strdup(path);
+#endif
     } else {
         addr->type = SOCKET_ADDRESS_LEGACY_KIND_INET;
         addr->u.inet.data = g_new(InetSocketAddress, 1);
diff --git a/chardev/char.c b/chardev/char.c
index 2ae4f46..5d52cd5 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -793,6 +793,9 @@ QemuOptsList qemu_chardev_opts = {
             .name = "path",
             .type = QEMU_OPT_STRING,
         },{
+            .name = "cmd",
+            .type = QEMU_OPT_STRING,
+        },{
             .name = "host",
             .type = QEMU_OPT_STRING,
         },{
diff --git a/qapi/char.json b/qapi/char.json
index ae19dcd..6de0f29 100644
--- a/qapi/char.json
+++ b/qapi/char.json
@@ -241,6 +241,10 @@
 #
 # @addr: socket address to listen on (server=true)
 #        or connect to (server=false)
+# @cmd: command to run via "sh -c" with stdin as one end of
+#       a AF_UNIX SOCK_DSTREAM socket pair. The other end
+#       is used by the chardev. Either an addr or a cmd can
+#       be specified, but not both.
 # @tls-creds: the ID of the TLS credentials object (since 2.6)
 # @server: create server socket (default: true)
 # @wait: wait for incoming connection on server
@@ -258,6 +262,7 @@
 # Since: 1.4
 ##
 { 'struct': 'ChardevSocket', 'data': { 'addr'       : 'SocketAddressLegacy',
+                                     '*cmd'       : 'str',
                                      '*tls-creds'  : 'str',
                                      '*server'    : 'bool',
                                      '*wait'      : 'bool',