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[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.

>From http://libvirt.org/internals/rpc.html#apiclientdispatch, I see:

 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

#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:
        buf[got] = '\0';

    return 0;

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