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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>
This commit is contained in:
Eric Blake 2017-09-05 14:11:12 -05:00
parent 3f5c4076f1
commit 9ffb827020
1 changed files with 10 additions and 2 deletions
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12
io/channel.c
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@ -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) {