systemtap stapvirt tool

[Stan Cox]

I am having a quandary with libvirt and am wondering if someone can shed 
some light.

Systemtap converts a probing and instrumentation language into a kernel 
module.  The module can optionally be run remotely via ssh or libvirt. 
The libvirt mechanism is not working (not yet sure of timing of 
regression)  The systemtap stap command pipes to a stapvirt command that 
is the libvirt interface.  The remote is running a stapsh tool that 
receives the requests.  The initial commands are sent and received okay 
(strace output on remote) but never receives the stap kernel module:

# local sent option data request
[pid 11959] read(3, "option data\n", 4096) = 12
# remote says OK
[pid 11959] write(3, "OK\n", 3)         = 3
[pid 11959] poll([{fd=3, events=POLLIN}, {fd=0, events=0}, {fd=0, 
events=0}], 3, -1) = 1 ([{fd=3, revents=POLLIN}])
[pid 11959] --- SIGIO {si_signo=SIGIO, si_code=SI_KERNEL} ---
[pid 11959] poll([{fd=3, events=POLLHUP}], 1, 0) = 0 (Timeout)
[pid 11959] rt_sigreturn({mask=[]})     = 1
# local sent file ... request to download the module
[pid 11959] read(3, "file 926928 stap_1f18b4b54e74602"..., 4096) = 58
# remote opens the module
[pid 11959] openat(AT_FDCWD, 
"stap_1f18b4b54e74602a0a1f0685f2f7333e_1006.ko", 
O_WRONLY|O_CREAT|O_TRUNC, 0666) = 4
# but never receives it
[pid 11959] read(3, "", 4096)           = 0


The local sets up callbacks for stdin, stdout, stream:
     ctxt.stdin_w = virEventAddHandle(STDIN_FILENO, 
VIR_EVENT_HANDLE_READABLE,
                                     stdin_event, &ctxt, NULL);
  ...
     ctxt.stdout_w = virEventAddHandle(STDOUT_FILENO, 0,
                                       stdout_event, &ctxt, NULL);
  ...
     virStreamEventAddCallback(ctxt.st, VIR_STREAM_EVENT_READABLE | 
VIR_EVENT_HANDLE_WRITABLE,
                                   stream_event, &ctxt, NULL) < 0)

Then starts an even loop
     while (!disconnect) {
         if (virEventRunDefaultImpl() != 0)
             break;
     }


stream_event is notified for the command requests, but is not notified 
for the kernel module chunks:

stdin_event excerpt:
         bytes_read = read(fd, ctxt->termbuf + ctxt->termbuf_off,
                               sizeof(ctxt->termbuf) - ctxt->termbuf_off);
  ...
         ctxt->termbuf_off += bytes_read;
  ...
     if (ctxt->termbuf_off) { // we have stuff to write to the stream
         virStreamEventUpdateCallback(ctxt->st, VIR_STREAM_EVENT_READABLE
                                              | VIR_STREAM_EVENT_WRITABLE);
     }

stream_event excerpt:

     if ((events & VIR_STREAM_EVENT_READABLE)
             && (ctxt->stbuf_off < sizeof(ctxt->stbuf))) {
         int bytes_recv = virStreamRecv(st, ctxt->stbuf + ctxt->stbuf_off,
                                        sizeof(ctxt->stbuf) - 
ctxt->stbuf_off);

I notice
  https://libvirt.org/html/libvirt-libvirt-stream.html
has an example using virStreamSend.  Is that the preferred way to do the 
above?