[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 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; }
On 23.01.2013 17:41, John Eckersberg wrote:
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 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; }
-- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
In order to use VIR_STREAM_NONBLOCK, you need to call virStreamEventAddCallback() which registers your stream in libvirtd event loop so data is sent to you as read from chardev's socket. However, you need a client event loop then. So the simple program should look like this [1]. Michal 1: http://pastebin.com/JffxfSmg
On Thu, Jan 24, 2013 at 10:14:33AM +0100, Michal Privoznik wrote:
On 23.01.2013 17:41, John Eckersberg wrote:
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 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; }
-- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
In order to use VIR_STREAM_NONBLOCK, you need to call virStreamEventAddCallback() which registers your stream in libvirtd event loop so data is sent to you as read from chardev's socket. However, you need a client event loop then. So the simple program should look like this [1].
Hmm, we ough tto have raised an error when he tried to create a stream with non-blocking flag set, but no event loop registered.
It is much better to include the code in your mail and not use pastebin links on the list. When people find this mail in google in 6 months time, chances are the pastebin link will be dead. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|
participants (3)
-
Daniel P. Berrange -
John Eckersberg -
Michal Privoznik