debugcon: support for debugging consoles (e.g. Bochs port 0xe9)

Add generic support for debugging consoles (simple I/O ports which
when written to cause debugging output to be written to a target.)
The current implementation matches Bochs' port 0xe9, allowing the same
debugging code to be used for both Bochs and Qemu.

There is no vm state associated with the debugging port, simply
because it has none -- the entire interface is a single, stateless,
write-only port.

Most of the code was cribbed from the serial port driver.

v2: removed non-ISA variants (they can be introduced when/if someone
wants them, using code from the serial port); added configurable
readback (Bochs returns 0xe9 on a read from this register, mimic that
by default)  This retains the apparently somewhat controversial user
friendly option, however.

v3: reimplemented the user friendly option as a synthetic option
("-debugcon foo" basically ends up being a parser-level shorthand for
"-chardev stdio,id=debugcon -device isa-debugcon,chardev=debugcon") --
this dramatically reduced the complexity while keeping the same level
of user friendliness.

v4: spaces, not tabs.

v5: update to match current top of tree.  Calling qemu_chr_open()
already during parsing no longer works; defer until we are parsing the
other console-like devices.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

Makefile.target

@@ -210,7 +210,7 @@ obj-i386-y += fdc.o mc146818rtc.o serial.o i8259.o i8254.o pcspk.o pc.o
 obj-i386-y += cirrus_vga.o apic.o ioapic.o parallel.o acpi.o piix_pci.o
 obj-i386-y += usb-uhci.o vmmouse.o vmport.o vmware_vga.o hpet.o
 obj-i386-y += device-hotplug.o pci-hotplug.o smbios.o wdt_ib700.o
-obj-i386-y += ne2000-isa.o
+obj-i386-y += ne2000-isa.o debugcon.o
 
 # shared objects
 obj-ppc-y = ppc.o ide/core.o ide/qdev.o ide/isa.o ide/pci.o ide/macio.o

hw/debugcon.c

@@ -0,0 +1,107 @@
+/*
+ * QEMU Bochs-style debug console ("port E9") emulation
+ *
+ * Copyright (c) 2003-2004 Fabrice Bellard
+ * Copyright (c) 2008 Citrix Systems, Inc.
+ * Copyright (c) Intel Corporation; author: H. Peter Anvin
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "hw.h"
+#include "qemu-char.h"
+#include "isa.h"
+#include "pc.h"
+
+//#define DEBUG_DEBUGCON
+
+typedef struct DebugconState {
+    CharDriverState *chr;
+    uint32_t readback;
+} DebugconState;
+
+typedef struct ISADebugconState {
+    ISADevice dev;
+    uint32_t iobase;
+    DebugconState state;
+} ISADebugconState;
+
+static void debugcon_ioport_write(void *opaque, uint32_t addr, uint32_t val)
+{
+    DebugconState *s = opaque;
+    unsigned char ch = val;
+
+#ifdef DEBUG_DEBUGCON
+    printf("debugcon: write addr=0x%04x val=0x%02x\n", addr, val);
+#endif
+
+    qemu_chr_write(s->chr, &ch, 1);
+}
+
+
+static uint32_t debugcon_ioport_read(void *opaque, uint32_t addr)
+{
+    DebugconState *s = opaque;
+
+#ifdef DEBUG_DEBUGCON
+    printf("debugcon: read addr=0x%04x\n", addr, val);
+#endif
+
+    return s->readback;
+}
+
+static void debugcon_init_core(DebugconState *s)
+{
+    if (!s->chr) {
+        fprintf(stderr, "Can't create debugcon device, empty char device\n");
+        exit(1);
+    }
+
+    qemu_chr_add_handlers(s->chr, NULL, NULL, NULL, s);
+}
+
+static int debugcon_isa_initfn(ISADevice *dev)
+{
+    ISADebugconState *isa = DO_UPCAST(ISADebugconState, dev, dev);
+    DebugconState *s = &isa->state;
+
+    debugcon_init_core(s);
+    register_ioport_write(isa->iobase, 1, 1, debugcon_ioport_write, s);
+    register_ioport_read(isa->iobase, 1, 1, debugcon_ioport_read, s);
+    return 0;
+}
+
+static ISADeviceInfo debugcon_isa_info = {
+    .qdev.name  = "isa-debugcon",
+    .qdev.size  = sizeof(ISADebugconState),
+    .init       = debugcon_isa_initfn,
+    .qdev.props = (Property[]) {
+        DEFINE_PROP_HEX32("iobase", ISADebugconState, iobase, 0xe9),
+        DEFINE_PROP_CHR("chardev",  ISADebugconState, state.chr),
+        DEFINE_PROP_HEX32("readback", ISADebugconState, state.readback, 0xe9),
+        DEFINE_PROP_END_OF_LIST(),
+    },
+};
+
+static void debugcon_register_devices(void)
+{
+    isa_qdev_register(&debugcon_isa_info);
+}
+
+device_init(debugcon_register_devices)

qemu-options.hx

@@ -1598,6 +1598,17 @@ STEXI
 Setup monitor on chardev @var{name}.
 ETEXI
 
+DEF("debugcon", HAS_ARG, QEMU_OPTION_debugcon, \
+    "-debugcon dev   redirect the debug console to char device 'dev'\n")
+STEXI
+@item -debugcon @var{dev}
+Redirect the debug console to host device @var{dev} (same devices as the
+serial port).  The debug console is an I/O port which is typically port
+0xe9; writing to that I/O port sends output to this device.
+The default device is @code{vc} in graphical mode and @code{stdio} in
+non graphical mode.
+ETEXI
+
 DEF("pidfile", HAS_ARG, QEMU_OPTION_pidfile, \
     "-pidfile file   write PID to 'file'\n")
 STEXI

vl.c

@@ -4748,6 +4748,7 @@ struct device_config {
         DEV_SERIAL,    /* -serial        */
         DEV_PARALLEL,  /* -parallel      */
         DEV_VIRTCON,   /* -virtioconsole */
+        DEV_DEBUGCON,  /* -debugcon */
     } type;
     const char *cmdline;
     QTAILQ_ENTRY(device_config) next;
@@ -4845,6 +4846,23 @@ static int virtcon_parse(const char *devname)
     return 0;
 }
 
+static int debugcon_parse(const char *devname)
+{   
+    QemuOpts *opts;
+
+    if (!qemu_chr_open("debugcon", devname, NULL)) {
+        exit(1);
+    }
+    opts = qemu_opts_create(&qemu_device_opts, "debugcon", 1);
+    if (!opts) {
+        fprintf(stderr, "qemu: already have a debugcon device\n");
+        exit(1);
+    }
+    qemu_opt_set(opts, "driver", "isa-debugcon");
+    qemu_opt_set(opts, "chardev", "debugcon");
+    return 0;
+}
+
 int main(int argc, char **argv, char **envp)
 {
     const char *gdbstub_dev = NULL;
@@ -5390,6 +5408,9 @@ int main(int argc, char **argv, char **envp)
                 add_device_config(DEV_PARALLEL, optarg);
                 default_parallel = 0;
                 break;
+            case QEMU_OPTION_debugcon:
+                add_device_config(DEV_DEBUGCON, optarg);
+                break;
 	    case QEMU_OPTION_loadvm:
 		loadvm = optarg;
 		break;
@@ -5927,6 +5948,8 @@ int main(int argc, char **argv, char **envp)
         exit(1);
     if (foreach_device_config(DEV_VIRTCON, virtcon_parse) < 0)
         exit(1);
+    if (foreach_device_config(DEV_DEBUGCON, debugcon_parse) < 0)
+        exit(1);
 
     module_call_init(MODULE_INIT_DEVICE);