qemu/0006-char-Equip-the-unix-tcp-backend-to-handle-nonblockin.patch

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From 6540bebbaa749d405df91516e1ca5a075e354628 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 96fc54e..53d2c13 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 {