[libvirt-users] pty pairing host - guest

Daniel P. Berrange berrange at redhat.com
Thu Mar 19 09:45:50 UTC 2015

On Thu, Mar 19, 2015 at 01:29:37PM +0530, Neel Basu wrote:
> HI!,
> I am using virt-manager GUI. There I can add a `Console Device`  through
> Add Hardware. I can add a virtio pty WITHOUT restarting the VM. also I get
> a pty allocated to host machine say `/dev/pty/M`
> My expectation is this `host:/dev/pty/M` is connected with a
> `guest:/dev/ttyN`. so If I open minicom or screen and write to
> `host:/dev/pty/M` it will be propagated to 'guest:/dev/ttyN'. Is my
> expectation correct ?
> If it is correct how will I know what is the guest tty allocated against
> this host pty ?

No, that's not how it works.  The <console> devices are exposed to
the guest as /dev/hvcNN devices. Starting with NN==0

> Similar to console device I can add a Serial device but that requires a
> reboot of the guest VM. However I tried that though I prefer to do it
> without a guest restart.
> <serial type='pty'>
>       <source path='/dev/pts/1'/>
>       <target port='0'/>
>       <alias name='serial0'/>
>  </serial>
> here also I expected host:/dev/pts/1 is paired with /dev/ttyS0 but couldn't
> communicate.

The serial port device supported is a 1990 era ISA bus serial port
so there's no hotplug for that. Only the paravirt consoles can be

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