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From 7ce910503a5db38f23a13ae5f56e256d80caf1e4 Mon Sep 17 00:00:00 2001
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From: Amit Shah <amit.shah@redhat.com>
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Date: Mon, 21 Mar 2011 22:05:10 +0100
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Subject: [PATCH] char: Throttle when host connection is down#
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When the host-side connection goes down, throttle the virtio-serial bus
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and later unthrottle when a connection gets established. This helps
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prevent any lost IO (guest->host) while the host connection was down.
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Bugzilla: 621484
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This commit actually helps the bug mentioned above as no writes will now
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get lost because of the throttling done here. With just the patches
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sent earlier for that bug, one write will end up getting lost in the
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worst case (host d/c, guest write, host connect).
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Signed-off-by: Amit Shah <amit.shah@redhat.com>
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Signed-off-by: Cole Robinson <crobinso@redhat.com>
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---
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qemu-char.c | 14 ++++++++++++++
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1 file changed, 14 insertions(+)
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diff --git a/qemu-char.c b/qemu-char.c
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index e7cd42a..5c71f0c 100644
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--- a/qemu-char.c
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+++ b/qemu-char.c
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@@ -140,6 +140,9 @@ static void qemu_chr_fire_open_event(void *opaque)
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{
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CharDriverState *s = opaque;
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qemu_chr_be_event(s, CHR_EVENT_OPENED);
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+ if (s->write_blocked) {
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+ char_write_unblocked(s);
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+ }
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qemu_free_timer(s->open_timer);
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s->open_timer = NULL;
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}
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@@ -2249,6 +2252,17 @@ static int tcp_chr_write(CharDriverState *chr, const uint8_t *buf, int len)
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ret = send_all(chr, s->fd, buf, len);
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if (ret == -1 && errno == EPIPE) {
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tcp_closed(chr);
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+
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+ if (chr->chr_enable_write_fd_handler && chr->chr_write_unblocked) {
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+ /*
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+ * Since we haven't written out anything, let's say
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+ * we're throttled. This will prevent any output from
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+ * the guest getting lost if host-side chardev goes
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+ * down. Unthrottle when we re-connect.
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+ */
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+ chr->write_blocked = true;
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+ return 0;
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+ }
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}
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return ret;
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} else {
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--
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1.8.1
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