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From 9fd3a478a3823258516f06201fa681e07dce1781 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 22:02:47 +0100
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Subject: [PATCH] char: Equip the unix/tcp backend to handle nonblocking
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writes#
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Now that the infrastructure is in place to return -EAGAIN to callers,
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individual char drivers can set their update_fd_handlers() function to
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set or remove an fd's write handler. This handler checks if the driver
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became writable.
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A generic callback routine is used for unblocking writes and letting
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users of chardevs know that a driver became writable again.
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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 | 27 +++++++++++++++++++++++++++
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1 file changed, 27 insertions(+)
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diff --git a/qemu-char.c b/qemu-char.c
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index 3d6e2f8..18e980d 100644
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--- a/qemu-char.c
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+++ b/qemu-char.c
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@@ -105,6 +105,19 @@
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static QTAILQ_HEAD(CharDriverStateHead, CharDriverState) chardevs =
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QTAILQ_HEAD_INITIALIZER(chardevs);
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+/*
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+ * Generic routine that gets called when chardev becomes writable.
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+ * Lets chardev user know it's OK to send more data.
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+ */
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+static void char_write_unblocked(void *opaque)
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+{
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+ CharDriverState *chr = opaque;
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+
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+ chr->write_blocked = false;
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+ chr->chr_disable_write_fd_handler(chr);
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+ chr->chr_write_unblocked(chr->handler_opaque);
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+}
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+
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void qemu_chr_be_event(CharDriverState *s, int event)
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{
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/* Keep track if the char device is open */
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@@ -126,6 +139,9 @@ 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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@@ -2245,6 +2261,17 @@ 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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