>From edcb78965b9cab18004c30721d46138000a2c810 Mon Sep 17 00:00:00 2001 From: Amit Shah Date: Mon, 21 Mar 2011 22:05:10 +0100 Subject: [PATCH 07/25] char: Throttle when host connection is down# When the host-side connection goes down, throttle the virtio-serial bus and later unthrottle when a connection gets established. This helps prevent any lost IO (guest->host) while the host connection was down. Bugzilla: 621484 This commit actually helps the bug mentioned above as no writes will now get lost because of the throttling done here. With just the patches sent earlier for that bug, one write will end up getting lost in the worst case (host d/c, guest write, host connect). Signed-off-by: Amit Shah --- qemu-char.c | 14 ++++++++++++++ 1 files changed, 14 insertions(+), 0 deletions(-) diff --git a/qemu-char.c b/qemu-char.c index f54ce04..8d39500 100644 --- a/qemu-char.c +++ b/qemu-char.c @@ -140,6 +140,9 @@ static void qemu_chr_generic_open_bh(void *opaque) { CharDriverState *s = opaque; qemu_chr_event(s, CHR_EVENT_OPENED); + if (s->write_blocked) { + char_write_unblocked(s); + } qemu_bh_delete(s->bh); s->bh = NULL; } @@ -2060,6 +2063,17 @@ 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 { -- 1.7.5.1