From 9fd3a478a3823258516f06201fa681e07dce1781 Mon Sep 17 00:00:00 2001

From: Amit Shah <amit.shah@redhat.com>

Date: Mon, 21 Mar 2011 22:02:47 +0100

Subject: [PATCH] char: Equip the unix/tcp backend to handle nonblocking

 writes#

Now that the infrastructure is in place to return -EAGAIN to callers,

individual char drivers can set their update_fd_handlers() function to

set or remove an fd's write handler.  This handler checks if the driver

became writable.

A generic callback routine is used for unblocking writes and letting

users of chardevs know that a driver became writable again.

Signed-off-by: Amit Shah <amit.shah@redhat.com>

Signed-off-by: Cole Robinson <crobinso@redhat.com>

---

 qemu-char.c | 27 +++++++++++++++++++++++++++

 1 file changed, 27 insertions(+)

diff --git a/qemu-char.c b/qemu-char.c

index 3d6e2f8..18e980d 100644

--- a/qemu-char.c

+++ b/qemu-char.c

@@ -105,6 +105,19 @@

 static QTAILQ_HEAD(CharDriverStateHead, CharDriverState) chardevs =

     QTAILQ_HEAD_INITIALIZER(chardevs);

+/*

+ * Generic routine that gets called when chardev becomes writable.

+ * Lets chardev user know it's OK to send more data.

+ */

+static void char_write_unblocked(void *opaque)

+{

+    CharDriverState *chr = opaque;

+

+    chr->write_blocked = false;

+    chr->chr_disable_write_fd_handler(chr);

+    chr->chr_write_unblocked(chr->handler_opaque);

+}

+

 void qemu_chr_be_event(CharDriverState *s, int event)

 {

     /* Keep track if the char device is open */

@@ -126,6 +139,9 @@ static void qemu_chr_fire_open_event(void *opaque)

 {

     CharDriverState *s = opaque;

     qemu_chr_be_event(s, CHR_EVENT_OPENED);

+    if (s->write_blocked) {

+        char_write_unblocked(s);

+    }

     qemu_free_timer(s->open_timer);

     s->open_timer = NULL;

 }

@@ -2245,6 +2261,17 @@ static int tcp_chr_write(CharDriverState *chr, const uint8_t *buf, int len)

         ret = send_all(chr, s->fd, buf, len);

         if (ret == -1 && errno == EPIPE) {

             tcp_closed(chr);

+

+            if (chr->chr_enable_write_fd_handler && chr->chr_write_unblocked) {

+                /*

+                 * Since we haven't written out anything, let's say

+                 * we're throttled.  This will prevent any output from

+                 * the guest getting lost if host-side chardev goes

+                 * down.  Unthrottle when we re-connect.

+                 */

+                chr->write_blocked = true;

+                return 0;

+            }

         }

         return ret;

     } else {