chardev: add baud parameter for serial host deviceserial-baud

When QEMU starts, it always changes the serial port parameters including baud
rate. This confused my guest which thought it was outputting at 9600 baud while
it was in fact changed to 115200.

After this patch, I can use `-serial /dev/ttyS0,baud=9600` to override the
default baud rate of 115200. Documentation is updated as well, so that users
know about the new `baud` parameter for `-serial` and `-chardev serial` (and its
alias `-chardev tty`).

Note that the baud option is not implemented for Windows. QEMU does not change
the default baud rate on Windows anyway. If somebody is going to implement it,
do not forget to update the documentation on "COM" devices which is also of
backend serial.

Signed-off-by: Peter Wu <lekensteyn@gmail.com>

3 files changed, 33 insertions, 13 deletions

diff --git a/qapi-schema.json b/qapi-schema.json
index 5ad6894738..f76bc0c2fb 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -3186,7 +3186,7 @@
 # Configuration info for device and pipe chardevs.
 #
 # @device: The name of the special file for the device,
-#          i.e. /dev/ttyS0 on Unix or COM1: on Windows
+#          i.e. /dev/parport0 on Unix.
 # @type: What kind of device this is.
 #
 # Since: 1.4
@@ -3194,6 +3194,20 @@
 { 'type': 'ChardevHostdev', 'data': { 'device' : 'str' } }
 
 ##
+# @ChardevSerial
+#
+# Configuration info for serial chardevs.
+#
+# @device: The name of the special file for the device,
+#          i.e. /dev/ttyS0 on Unix or COM1: on Windows
+# @baud: #optional baud rate to set for host device. (default 115200)
+#
+# Since: 1.5
+##
+{ 'type': 'ChardevSerial', 'data': { 'device' : 'str',
+                                     '*baud': 'int' } }
+
+##
 # @ChardevSocket:
 #
 # Configuration info for (stream) socket chardevs.
@@ -3311,7 +3325,7 @@
 { 'type': 'ChardevDummy', 'data': { } }
 
 { 'union': 'ChardevBackend', 'data': { 'file'   : 'ChardevFile',
-                                       'serial' : 'ChardevHostdev',
+                                       'serial' : 'ChardevSerial',
                                        'parallel': 'ChardevHostdev',
                                        'pipe'   : 'ChardevHostdev',
                                        'socket' : 'ChardevSocket',
diff --git a/qemu-char.c b/qemu-char.c
index d04b429a03..421730a79c 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -1450,11 +1450,11 @@ static void qemu_chr_close_tty(CharDriverState *chr)
     }
 }
 
-static CharDriverState *qemu_chr_open_tty_fd(int fd)
+static CharDriverState *qemu_chr_open_tty_fd(int fd, int baud)
 {
     CharDriverState *chr;
 
-    tty_serial_init(fd, 115200, 'N', 8, 1);
+    tty_serial_init(fd, baud, 'N', 8, 1);
     chr = qemu_chr_open_fd(fd, fd);
     chr->chr_ioctl = tty_serial_ioctl;
     chr->chr_close = qemu_chr_close_tty;
@@ -3155,13 +3155,15 @@ static void qemu_chr_parse_serial(QemuOpts *opts, ChardevBackend *backend,
                                   Error **errp)
 {
     const char *device = qemu_opt_get(opts, "path");
+    const int baud = qemu_opt_get_number(opts, "baud", 115200);
 
     if (device == NULL) {
         error_setg(errp, "chardev: serial/tty: no device path given");
         return;
     }
-    backend->serial = g_new0(ChardevHostdev, 1);
+    backend->serial = g_new0(ChardevSerial, 1);
     backend->serial->device = g_strdup(device);
+    backend->serial->baud = baud;
 }
 
 static void qemu_chr_parse_parallel(QemuOpts *opts, ChardevBackend *backend,
@@ -3590,7 +3592,7 @@ static CharDriverState *qmp_chardev_open_file(ChardevFile *file, Error **errp)
     return qemu_chr_open_win_file(out);
 }
 
-static CharDriverState *qmp_chardev_open_serial(ChardevHostdev *serial,
+static CharDriverState *qmp_chardev_open_serial(ChardevSerial *serial,
                                                 Error **errp)
 {
     return qemu_chr_open_win_path(serial->device);
@@ -3639,7 +3641,7 @@ static CharDriverState *qmp_chardev_open_file(ChardevFile *file, Error **errp)
     return qemu_chr_open_fd(in, out);
 }
 
-static CharDriverState *qmp_chardev_open_serial(ChardevHostdev *serial,
+static CharDriverState *qmp_chardev_open_serial(ChardevSerial *serial,
                                                 Error **errp)
 {
 #ifdef HAVE_CHARDEV_TTY
@@ -3650,7 +3652,7 @@ static CharDriverState *qmp_chardev_open_serial(ChardevHostdev *serial,
         return NULL;
     }
     qemu_set_nonblock(fd);
-    return qemu_chr_open_tty_fd(fd);
+    return qemu_chr_open_tty_fd(fd, serial->baud);
 #else
     error_setg(errp, "character device backend type 'serial' not supported");
     return NULL;
diff --git a/qemu-options.hx b/qemu-options.hx
index bf94862b58..5f20edd923 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1794,8 +1794,8 @@ DEF("chardev", HAS_ARG, QEMU_OPTION_chardev,
 #endif
 #if defined(__linux__) || defined(__sun__) || defined(__FreeBSD__) \
         || defined(__NetBSD__) || defined(__OpenBSD__) || defined(__DragonFly__)
-    "-chardev serial,id=id,path=path[,mux=on|off]\n"
-    "-chardev tty,id=id,path=path[,mux=on|off]\n"
+    "-chardev serial,id=id,path=path[,mux=on|off][,baud=baud]\n"
+    "-chardev tty,id=id,path=path[,mux=on|off][,baud=baud]\n"
 #endif
 #if defined(__linux__) || defined(__FreeBSD__) || defined(__DragonFly__)
     "-chardev parallel,id=id,path=path[,mux=on|off]\n"
@@ -1963,7 +1963,7 @@ take any options.
 
 @option{console} is only available on Windows hosts.
 
-@item -chardev serial ,id=@var{id} ,path=@option{path}
+@item -chardev serial ,id=@var{id} ,path=@option{path} [,baud=@option{baud}]
 
 Send traffic from the guest to a serial device on the host.
 
@@ -1972,6 +1972,9 @@ not only serial lines.
 
 @option{path} specifies the name of the serial device to open.
 
+On Unix hosts, the @option{baud} specifies the baud rate for the host serial
+device. It is optional and defaults to 115200.
+
 @item -chardev pty ,id=@var{id}
 
 Create a new pseudo-terminal on the host and connect to it. @option{pty} does
@@ -2404,9 +2407,10 @@ vc:80Cx24C
 No device is allocated.
 @item null
 void device
-@item /dev/XXX
+@item /dev/XXX[,baud=@var{baud}]
 [Linux only] Use host tty, e.g. @file{/dev/ttyS0}. The host serial port
-parameters are set according to the emulated ones.
+parameters are set according to the emulated ones. The optional @var{baud}
+option allows for overriding the default host baud rate of 115200.
 @item /dev/parport@var{N}
 [Linux only, parallel port only] Use host parallel port
 @var{N}. Currently SPP and EPP parallel port features can be used.