vl.c: Provide accessor function serial_hd() for serial_hds[] array

Provide an accessor function serial_hd() to return the Chardev
(if any) associated with the numbered serial port. This will
be used to replace direct accesses to the serial_hds[] array,
so that calling code doesn't need to care about the size of
that array.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180420145249.32435-7-peter.maydell@linaro.org

include/sysemu/sysemu.h

@@ -163,6 +163,9 @@ void hmp_pcie_aer_inject_error(Monitor *mon, const QDict *qdict);
 
 extern Chardev *serial_hds[MAX_SERIAL_PORTS];
 
+/* Return the Chardev for serial port i, or NULL if none */
+Chardev *serial_hd(int i);
+
 /* parallel ports */
 
 #define MAX_PARALLEL_PORTS 3

vl.c

@@ -2516,6 +2516,15 @@ static int serial_parse(const char *devname)
     return 0;
 }
 
+Chardev *serial_hd(int i)
+{
+    assert(i >= 0);
+    if (i < ARRAY_SIZE(serial_hds)) {
+        return serial_hds[i];
+    }
+    return NULL;
+}
+
 static int parallel_parse(const char *devname)
 {
     static int index = 0;