Re: Help with reading from hvc console device on a PV guest

[Wei Liu <wei.liu2@citrix.com>]

Please don't top-post.

On Fri, Jul 24, 2015 at 10:05:20AM -0700, sainath grandhi wrote:
> Hi Wei,
>    Thanks for your reply. Sorry I did not change the comment properly.
> These are the two methods I tried separately.
> 
> First method:
>      I see /dev/hvc1 and /dev/hvc2 being created when I give two
> channels in the guest xl config file. So I wrote a program to open
> hvc1 and read like below.
> fd=open("/dev/hvc1", O_RDWR|O_NONBLOCK)
> 
> 
> Second method:
>      I also notice the devices are created under
> /sys/bus/xen/devices/console-1 and console-2. And the corresponding
> devices are in /dev/hvc1 and /dev/hvc2.
>  So I manually created devices similar to following udev rules like
> below for console 1.
> 
> HVC_MAJOR=229
> 
> NAME_PATH=device/console/1/name
> 
> NAME=$(xenstore-read $NAME_PATH)
> 
> mknod /dev/xenconsole/$NAME c $HVC_MAJOR 1
> 
> ln -s /dev/xenconsole/$NAME /dev/xenconsole/console-1
> 
> NAME in my case is xen.channel.1 Hence I tried to open and read using
> fd=open("/dev/xenconsole/xen.channel.1", O_RDWR|O_NONBLOCK)
> 

Looks like that you have all udev rules in place. Good.

> 
> But both the attempts failed. And they do not read the contents I sent
> from dom0. What I notice from the code review of hvc driver is that
> any data that the hvc driver gets from the backend is used ONLY for
> terminal consumption and not for file operations?
> 

Not sure, I've never used that myself.

I've CC'ed Dave Scott who might have better idea about how channel is
supposed to be used.

> When I tried to create a console login on the hvc2, and do a socat on
> the socket path from dom0, I am able to send commands like ls, pwd
> etc. and receive responses fine.
> 

This means the channel is created OK.

Wei.

> 
> Thanks
> -Sainath
> 
> On Fri, Jul 24, 2015 at 12:54 AM, Wei Liu <wei.liu2@citrix.com> wrote:
> > On Thu, Jul 23, 2015 at 10:14:57AM -0700, sainath grandhi wrote:
> >> Hello,
> >>
> >>     Please let me know if you have some information about issue below.
> >>
> >>     I created a channel device for PV guest using
> >>
> >> channel= ["connection=pty, name=xen.channel.0,
> >> path=/var/lib/xen/ctl-socket","connection=socket, name=xen.channel.1,
> >> path=/var/lib/xen/ctl-socket-data"]
> >>
> >>    Xen toolstack uses qemu backend for additional consoles other than console 0.
> >>
> >> /usr/local/lib/xen/bin/qemu-system-i386 -xen-domid 505 -chardev
> >> socket,id=libxl-cmd,path=/var/run/xen/qmp-libxl-505,server,nowait
> >> -no-shutdown -mon chardev=libxl-cmd,mode=control -chardev
> >> socket,id=libxenstat-cmd,path=/var/run/xen/qmp-libxenstat-505,server,nowait
> >> -mon chardev=libxenstat-cmd,mode=control -chardev
> >> pty,id=libxl-channel0 -chardev
> >> socket,id=libxl-channel1,path=/var/lib/xen/ctl-socket-data,server,nowait
> >> -nodefaults -xen-attach -name ubuntupvhchannel -vnc none -display none
> >> -nographic -machine xenpv -m 2048
> >>
> >>    I see additional console devices in the guest under /dev/hvc1 and /dev/hvc2.
> >>
> >>   I write to the other end of the channel i.e. from dom0,   but when I
> >> read the console device /dev/hvc1 or /dev/hvc2, using cat or an
> >> application using read(), I do not get the data out. But I could print
> >> out the data using printk (the string I passed from dom0) inside the
> >> hvc driver code where it reads from backend.
> >>
> >>   Looks like I am missing something in the userspace creation of
> >> device node or some flag for opening device file in the read system
> >> call of my application. Any suggestions?
> >>
> >> Application I wrote to read from console device:
> >>
> >>   memset(buf, 0, sizeof(buf));
> >>
> >>   fd=open("/dev/xenconsole/xen.channel.1", O_RDWR|O_NONBLOCK);
> >>
> >
> > Have you checked if there is such device under the said directory?
> >
> > You need to have udev rules in guest to create those devices for you.
> >
> > See the discussion thread at
> >
> >    <alpine.DEB.2.02.1506241241110.18681@kaball.uk.xensource.com>
> >
> >>   if(fd < 0)
> >>
> >>       printf("could not open dev hvc2\n");
> >>
> >
> > I'm confused because the code says hvc2 here but open() has another path
> > in it.
> >
> > Wei.
> >
> >>   size = read(fd, (void *)buf, sizeof(buf));
> >>
> >>   printf("size read %d\n",size);
> >>
> >> Thanks
> >>
> >> _______________________________________________
> >> Xen-devel mailing list
> >> Xen-devel@lists.xen.org
> >> http://lists.xen.org/xen-devel