From 280e240cfa8e633dd062791b1d0d62fe0e642d46 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@redhat.com>
Date: Sat, 2 Dec 2017 12:19:38 +0100
Subject: [PATCH 12/36] io: Yield rather than wait when already in coroutine

RH-Author: Paolo Bonzini <pbonzini@redhat.com>
Message-id: <20171202121953.13317-3-pbonzini@redhat.com>
Patchwork-id: 78076
O-Subject: [RHEL7.4 qemu-kvm-rhev PATCH 02/17] io: Yield rather than wait when already in coroutine
Bugzilla: 1464908
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
RH-Acked-by: John Snow <jsnow@redhat.com>

From: Eric Blake <eblake@redhat.com>

The new qio_channel_{read,write}{,v}_all functions are documented
as yielding until data is available.  When used on a blocking
channel, this yield is done via qio_channel_wait() which spawns
a nested event loop under the hood (so it is that secondary loop
which yields as needed); but if we are already in a coroutine (at
which point QIO_CHANNEL_ERR_BLOCK is only possible if we are a
non-blocking channel), we want to yield the current coroutine
instead of spawning a nested event loop.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20170905191114.5959-2-eblake@redhat.com>
Acked-by: Daniel P. Berrange <berrange@redhat.com>
[commit message updated]
Signed-off-by: Eric Blake <eblake@redhat.com>
(cherry picked from commit 9ffb8270205a274a18ee4f8a735e2fccaf957246)

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 io/channel.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/io/channel.c b/io/channel.c
index 5e8c2f0..9e62794 100644
--- a/io/channel.c
+++ b/io/channel.c
@@ -105,7 +105,11 @@ int qio_channel_readv_all(QIOChannel *ioc,
         ssize_t len;
         len = qio_channel_readv(ioc, local_iov, nlocal_iov, errp);
         if (len == QIO_CHANNEL_ERR_BLOCK) {
-            qio_channel_wait(ioc, G_IO_IN);
+            if (qemu_in_coroutine()) {
+                qio_channel_yield(ioc, G_IO_IN);
+            } else {
+                qio_channel_wait(ioc, G_IO_IN);
+            }
             continue;
         } else if (len < 0) {
             goto cleanup;
@@ -143,7 +147,11 @@ int qio_channel_writev_all(QIOChannel *ioc,
         ssize_t len;
         len = qio_channel_writev(ioc, local_iov, nlocal_iov, errp);
         if (len == QIO_CHANNEL_ERR_BLOCK) {
-            qio_channel_wait(ioc, G_IO_OUT);
+            if (qemu_in_coroutine()) {
+                qio_channel_yield(ioc, G_IO_OUT);
+            } else {
+                qio_channel_wait(ioc, G_IO_OUT);
+            }
             continue;
         }
         if (len < 0) {
-- 
1.8.3.1