I am trying to write a simple app which connects a channel obtained from virDomainOpenChannel() to stdin/stdout (based in part on the snippet at [1]). However, it seems like the data received back from the stream is delayed by one iteration. It would be hard to explain this by simply showing the output, so here's a timeline instead: 1. start the program on the host 2. write "msg from host<Enter>" 3. socat on the guest sees this right away 4. from the guest's socat, write "msg from guest<Enter>" 5. the reply does not show up on the host until AFTER you press <Enter> (which of course also sends a newline to the guest) 6. this 'one line delay' occurs throughout the conversation, receiving guest replies to things sent two <Enter>s ago Doing socat on both sides work as expected. Also, using a blocked stream and a thread for sending and another for receiving works as well. It would be nice however if I could get rid of the threads in favour of callbacks. Not sure if I'm missing something obvious. Thanks, Jonathan [1] https://www.redhat.com/archives/libvir-list/2012-December/msg01084.html --- #include <ctype.h> #include <err.h> #include <errno.h> #include <stdlib.h> #include <stdio.h> #include <string.h> #include <libvirt/libvirt.h> #include <fcntl.h> #define CONNECT_URI "qemu:///system" #define DOMAIN "TestVM" #define CHANNEL "channel.0" #define BUF_SIZE 80 int stream_active = 1; void stdin_to_stream(int watch, int fd, int events, void *opaque) { virStreamPtr stream = *((virStreamPtr*)(opaque)); if (events & VIR_EVENT_HANDLE_READABLE) { char buf[1024]; int bytes_read = read(fd, buf, sizeof(buf)); if (bytes_read > 0) virStreamSend(stream, buf, bytes_read); } if (events & (VIR_EVENT_HANDLE_ERROR|VIR_EVENT_HANDLE_HANGUP)) { stream_active = 0; } return; } void stream_to_stdout(virStreamPtr stream, int events, void *opaque) { if (events & VIR_EVENT_HANDLE_READABLE) { char buf[1024]; int bytes_read = virStreamRecv(stream, buf, sizeof(buf)); if (bytes_read > 0) { fwrite(buf, bytes_read, 1, stdout); fflush(stdout); } } if (events & (VIR_EVENT_HANDLE_ERROR|VIR_EVENT_HANDLE_HANGUP)) { stream_active = 0; } return; } int main(int argc, char *argv[]) { virConnectPtr conn; virDomainPtr dom; virStreamPtr st; int bytes_read; char buf[BUF_SIZE]; if ((conn = virConnectOpen(CONNECT_URI)) == NULL) errx(1, "virConnectOpen"); if ((dom = virDomainLookupByName(conn, DOMAIN)) == NULL) errx(1, "virDomainLookupByName"); if ((st = virStreamNew(conn, VIR_STREAM_NONBLOCK)) == NULL) errx(1, "virStreamNew"); if (virDomainOpenChannel(dom, CHANNEL, st, 0) == -1) errx(1, "virDomainOpenChannel"); if (virEventRegisterDefaultImpl() != 0) errx(1, "virEventRegisterDefaultImpl"); if (virStreamEventAddCallback(st, 1|4|8, stream_to_stdout, NULL, NULL) != 0) errx(1, "virStreamEventAddCallback"); int flags = fcntl(fileno(stdin), F_GETFL) | O_NONBLOCK; fcntl(fileno(stdin), F_SETFL, flags); if (virEventAddHandle(fileno(stdin), 1|4|8, stdin_to_stream, &st, NULL) < 0) errx(1, "virEventAddHandle"); while (stream_active) { if (virEventRunDefaultImpl() != 0) { errx(1, "virEventRunDefaultImpl"); break; } } if (virStreamFinish(st) < 0) errx(1, "virStreamFinish"); if (virStreamFree(st) < 0) errx(1, "virStreamFree"); return 0; }