From: Eric Blake <eblake@redhat.com>

Date: Tue, 5 Sep 2017 14:11:12 -0500

Subject: [PATCH] io: Yield rather than wait when already in coroutine

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>

---

 io/channel.c | 12 ++++++++++--

 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/io/channel.c b/io/channel.c

index 5e8c2f0a91..9e62794cab 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) {