backends: Introduce chr-testdev

From: Paolo Bonzini <pbonzini@redhat.com>

chr-testdev enables a virtio serial channel to be used for guest
initiated qemu exits. hw/misc/debugexit already enables guest
initiated qemu exits, but only for PC targets. chr-testdev supports
any virtio-capable target. kvm-unit-tests/arm is already making use
of this backend.

Currently there is a single command implemented, "q".  It takes a
(prefix) argument for the exit code, thus an exit is implemented by
writing, e.g. "1q", to the virtio-serial port.

It can be used as:
   $QEMU ... \
     -device virtio-serial-device \
     -device virtserialport,chardev=ctd -chardev testdev,id=ctd

or, use:
   $QEMU ... \
     -device virtio-serial-device \
     -device virtconsole,chardev=ctd -chardev testdev,id=ctd

to bind it to virtio-serial port0.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

backends/testdev.c

@@ -0,0 +1,131 @@
+/*
+ * QEMU Char Device for testsuite control
+ *
+ * Copyright (c) 2014 Red Hat, Inc.
+ *
+ * Author: Paolo Bonzini <pbonzini@redhat.com>
+ *
+ * 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 "qemu-common.h"
+#include "sysemu/char.h"
+
+#define BUF_SIZE 32
+
+typedef struct {
+    CharDriverState *chr;
+    uint8_t in_buf[32];
+    int in_buf_used;
+} TestdevCharState;
+
+/* Try to interpret a whole incoming packet */
+static int testdev_eat_packet(TestdevCharState *testdev)
+{
+    const uint8_t *cur = testdev->in_buf;
+    int len = testdev->in_buf_used;
+    uint8_t c;
+    int arg;
+
+#define EAT(c) do { \
+    if (!len--) {   \
+        return 0;   \
+    }               \
+    c = *cur++;     \
+} while (0)
+
+    EAT(c);
+
+    while (isspace(c)) {
+        EAT(c);
+    }
+
+    arg = 0;
+    while (isdigit(c)) {
+        arg = arg * 10 + c - '0';
+        EAT(c);
+    }
+
+    while (isspace(c)) {
+        EAT(c);
+    }
+
+    switch (c) {
+    case 'q':
+        exit((arg << 1) | 1);
+        break;
+    default:
+        break;
+    }
+    return cur - testdev->in_buf;
+}
+
+/* The other end is writing some data.  Store it and try to interpret */
+static int testdev_write(CharDriverState *chr, const uint8_t *buf, int len)
+{
+    TestdevCharState *testdev = chr->opaque;
+    int tocopy, eaten, orig_len = len;
+
+    while (len) {
+        /* Complete our buffer as much as possible */
+        tocopy = MIN(len, BUF_SIZE - testdev->in_buf_used);
+
+        memcpy(testdev->in_buf + testdev->in_buf_used, buf, tocopy);
+        testdev->in_buf_used += tocopy;
+        buf += tocopy;
+        len -= tocopy;
+
+        /* Interpret it as much as possible */
+        while (testdev->in_buf_used > 0 &&
+               (eaten = testdev_eat_packet(testdev)) > 0) {
+            memmove(testdev->in_buf, testdev->in_buf + eaten,
+                    testdev->in_buf_used - eaten);
+            testdev->in_buf_used -= eaten;
+        }
+    }
+    return orig_len;
+}
+
+static void testdev_close(struct CharDriverState *chr)
+{
+    TestdevCharState *testdev = chr->opaque;
+
+    g_free(testdev);
+}
+
+CharDriverState *chr_testdev_init(void)
+{
+    TestdevCharState *testdev;
+    CharDriverState *chr;
+
+    testdev = g_malloc0(sizeof(TestdevCharState));
+    testdev->chr = chr = g_malloc0(sizeof(CharDriverState));
+
+    chr->opaque = testdev;
+    chr->chr_write = testdev_write;
+    chr->chr_close = testdev_close;
+
+    return chr;
+}
+
+static void register_types(void)
+{
+    register_char_driver_qapi("testdev", CHARDEV_BACKEND_KIND_TESTDEV, NULL);
+}
+
+type_init(register_types);