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[Qemu-devel] [PATCH v2 1/1] qemu-char: socket backend: disconnect on wri
From: |
Denis V. Lunev |
Subject: |
[Qemu-devel] [PATCH v2 1/1] qemu-char: socket backend: disconnect on write error |
Date: |
Thu, 2 Feb 2017 16:18:24 +0300 |
From: Anton Nefedov <address@hidden>
Socket backend read handler should normally perform a disconnect, however
the read handler may not get a chance to run if the frontend is not ready
(qemu_chr_be_can_write() == 0).
This means that in virtio-serial frontend case if
- the host has disconnected (giving EPIPE on socket write)
- and the guest has disconnected (-> frontend not ready -> backend
will not read)
- and there is still data (frontend->backend) to flush (has to be a really
tricky timing but nevertheless, we have observed the case in production)
This results in virtio-serial trying to flush this data continiously forming
a busy loop.
Solution: react on write error in the socket write handler.
errno is not reliable after qio_channel_writev_full(), so we may not get
the exact EPIPE, so disconnect on any error but QIO_CHANNEL_ERR_BLOCK which
io_channel_send_full() converts to errno EAGAIN.
We must not disconnect right away though, there still may be data to read
(see 4bf1cb0).
Signed-off-by: Anton Nefedov <address@hidden>
Signed-off-by: Denis V. Lunev <address@hidden>
CC: Paolo Bonzini <address@hidden>
CC: Daniel P. Berrange <address@hidden>
CC: Marc-André Lureau <address@hidden>
---
Changes from v1:
- we do not rely on EPIPE anynore. Socket should be closed on all errors
except EAGAIN
chardev/char-socket.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/chardev/char-socket.c b/chardev/char-socket.c
index 4068dc5..e2137aa 100644
--- a/chardev/char-socket.c
+++ b/chardev/char-socket.c
@@ -97,6 +97,9 @@ static gboolean tcp_chr_accept(QIOChannel *chan,
GIOCondition cond,
void *opaque);
+static int tcp_chr_read_poll(void *opaque);
+static void tcp_chr_disconnect(CharDriverState *chr);
+
/* Called with chr_write_lock held. */
static int tcp_chr_write(Chardev *chr, const uint8_t *buf, int len)
{
@@ -114,6 +117,13 @@ static int tcp_chr_write(Chardev *chr, const uint8_t *buf,
int len)
s->write_msgfds_num = 0;
}
+ if (ret < 0 && errno != EAGAIN) {
+ if (tcp_chr_read_poll(chr) <= 0) {
+ tcp_chr_disconnect(chr);
+ return len;
+ } /* else let the read handler finish it properly */
+ }
+
return ret;
} else {
/* XXX: indicate an error ? */
--
2.7.4
- [Qemu-devel] [PATCH v2 1/1] qemu-char: socket backend: disconnect on write error,
Denis V. Lunev <=