From b1f45e402af97406d4dd2fb998f419d342b88384 Mon Sep 17 00:00:00 2001 From: Amit Shah Date: Fri, 4 Feb 2011 08:20:49 -0200 Subject: [RHEL6 qemu-kvm PATCH 18/27] char: Throttle when host connection is down RH-Author: Amit Shah Message-id: Patchwork-id: 17719 O-Subject: [RHEL6.1 qemu PATCH v5 18/19] char: Throttle when host connection is down Bugzilla: 588916 RH-Acked-by: Alon Levy RH-Acked-by: Juan Quintela RH-Acked-by: Jes Sorensen 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(-) Signed-off-by: Eduardo Habkost --- qemu-char.c | 14 ++++++++++++++ 1 files changed, 14 insertions(+), 0 deletions(-) diff --git a/qemu-char.c b/qemu-char.c index dc3e930..bd7dc92 100644 --- a/qemu-char.c +++ b/qemu-char.c @@ -132,6 +132,9 @@ 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; } @@ -2017,6 +2020,17 @@ 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 { -- 1.7.3.2