[libvirt] Non-blocking virStreamRecv always returns -2 (EAGAIN)?
I'm running the following test program, and it works as written with a
blocking stream. Inside the guest I'm running:
[root@f17-minimal ~]# socat /usr/share/dict/words
/dev/virtio-ports/org.libguestfs.channel.0
As expected on the client side, I get all the words dumped. However if
I swap the virStreamNew lines and instead use the non-blocking stream,
the virStreamRecv call always returns -2.
When no thread is performing any RPC method call, or sending stream
data there is still a need to monitor the socket for incoming I/O
related to asynchronous events, or stream data receipt. For this task,
a watch is registered with the event loop which triggers whenever the
socket is readable. This watch is automatically disabled whenever any
other thread grabs the buck, and re-enabled when the buck is released.
If I understand that correctly, shouldn't the watch be responsible for
reading the stream data in this case? Or am I just completely missing
something?
-----
#include <libvirt.h>
int main()
{
virConnectPtr conn;
virDomainPtr dom;
virStreamPtr st;
char buf[1024+1];
int got = 0;
conn = virConnectOpen("qemu+ssh://root@localhost/system");
dom = virDomainLookupByName(conn, "f17-minimal");
/* st = virStreamNew(conn, VIR_STREAM_NONBLOCK); */
st = virStreamNew(conn, 0);
virDomainOpenChannel(dom, "org.libguestfs.channel.0", st, 0);
while (1) {
got = virStreamRecv(st, buf, 1024);
switch (got) {
case 0:
goto finish;
case -1:
goto free;
case -2:
puts("Retrying");
sleep(1);
continue;
}
buf[got] = '\0';
puts(buf);
}
finish:
virStreamFinish(st);
free:
virStreamFree(st);
return 0;
}