From 625915146f56f77c275be1aee160f40183008b8d 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 | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/qemu-char.c b/qemu-char.c
index b46cc97..9f8608a 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -106,6 +106,19 @@
 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 */
@@ -2503,6 +2516,25 @@ static void tcp_chr_close(CharDriverState *chr)
     qemu_chr_be_event(chr, CHR_EVENT_CLOSED);
 }
 
+static void tcp_enable_write_fd_handler(CharDriverState *chr)
+{
+    TCPCharDriver *s = chr->opaque;
+
+    /*
+     * This function is called only after tcp_chr_connect() is called
+     * (either in 'server' mode or client mode.  So we're sure of
+     * s->fd being initialised.
+     */
+    enable_write_fd_handler(s->fd, char_write_unblocked);
+}
+
+static void tcp_disable_write_fd_handler(CharDriverState *chr)
+{
+    TCPCharDriver *s = chr->opaque;
+
+    disable_write_fd_handler(s->fd);
+}
+
 static CharDriverState *qemu_chr_open_socket(QemuOpts *opts)
 {
     CharDriverState *chr = NULL;
@@ -2557,6 +2589,8 @@ static CharDriverState *qemu_chr_open_socket(QemuOpts *opts)
     chr->chr_close = tcp_chr_close;
     chr->get_msgfd = tcp_get_msgfd;
     chr->chr_add_client = tcp_chr_add_client;
+    chr->chr_enable_write_fd_handler = tcp_enable_write_fd_handler;
+    chr->chr_disable_write_fd_handler = tcp_disable_write_fd_handler;
 
     if (is_listen) {
         s->listen_fd = fd;
-- 
1.7.12.1