xen/console: introduce a 'w' debug-key that dumps the console ring

This patch adds a new 'w' debug-key, chosen from the limited remaining
keys only due to its proximity to 'q', that dumps the console ring to
configured console devices. It's useful to for tracking down how an
unresponsive system got into a broken state via serial console.

Signed-off-by: Matt Wilson <msw@amazon.com>
Committed-by: Keir Fraser <keir@xen.org>

1 files changed, 45 insertions, 0 deletions

diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index d97170c641..9e1adb50f7 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -264,6 +264,49 @@ static void sercon_puts(const char *s)
         serial_puts(sercon_handle, s);
 }
 
+static void dump_console_ring_key(unsigned char key)
+{
+    uint32_t idx, len, sofar, c;
+    unsigned int order;
+    char *buf;
+
+    printk("'%c' pressed -> dumping console ring buffer (dmesg)\n", key);
+
+    /* create a buffer in which we'll copy the ring in the correct
+       order and NUL terminate */
+    order = get_order_from_bytes(conring_size + 1);
+    buf = alloc_xenheap_pages(order, 0);
+    if ( buf == NULL )
+    {
+        printk("unable to allocate memory!\n");
+        return;
+    }
+
+    c = conringc;
+    sofar = 0;
+    while ( (c != conringp) )
+    {
+        idx = CONRING_IDX_MASK(c);
+        len = conringp - c;
+        if ( (idx + len) > conring_size )
+            len = conring_size - idx;
+        memcpy(buf + sofar, &conring[idx], len);
+        sofar += len;
+        c += len;
+    }
+    buf[sofar] = '\0';
+
+    sercon_puts(buf);
+    vga_puts(buf);
+
+    free_xenheap_pages(buf, order);
+}
+
+static struct keyhandler dump_console_ring_keyhandler = {
+    .u.fn = dump_console_ring_key,
+    .desc = "synchronously dump console ring buffer (dmesg)"
+};
+
 /* CTRL-<switch_char> switches input direction between Xen and DOM0. */
 #define switch_code (opt_conswitch[0]-'a'+1)
 static int __read_mostly xen_rx = 1; /* FALSE => serial input passed to domain 0. */
@@ -661,6 +704,8 @@ void __init console_endboot(void)
     if ( opt_conswitch[1] == 'x' )
         xen_rx = !xen_rx;
 
+    register_keyhandler('w', &dump_console_ring_keyhandler);
+
     /* Serial input is directed to DOM0 by default. */
     switch_serial_input();
 }