Re: [Xen-devel] [PATCH v4] add support for libvirt-like channels

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 7 Aug 2014, David Vrabel wrote:
> On 07/08/14 14:37, Dave Scott wrote:
> > 
> > On 28 Jul 2014, at 15:22, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
> > 
> >> On 22/07/14 16:05, David Scott wrote:
> >>>
> >>> Note: I've seen a problem with some Linux console frontends which attempt
> >>> to overwrite the read-only key 'type' (= xenconsoled|ioemu) in the 
> >>> frontend
> >>> directory. [ this key is already present, it's not added by these patches 
> >>> ]
> >>> Since 'type' refers to the toolstack's choice of implementation service
> >>> (which is none of the guest's business) I think the read/only permissions
> >>> are right. The location of the key is not ideal (it should be in the
> >>> backend directory IMHO) but this is the case with several other keys 
> >>> located
> >>> in the frontend such as 'limit' and 'tty'. I think this is a Linux 
> >>> frontend
> >>> bug which should be fixed there. These patches work with Mirage VMs and
> >>> with Linux if I workaround the permissions by giving the guest read/write
> >>> to the 'type' key. 
> >>
> >> Which Linux front ends?
> > 
> > I just tested a Debian jessie with
> > 
> >   # uname -a
> >   Linux jessie 3.13-6-686-pae #1 SMP Debian 3.13.5-1 (2014-03-04) i686 
> > GNU/Linux
> > 
> > In my xenstored access log I see:
> > 
> >   Aug  7 14:28:30 localhost xenstored:  D40.6        write     
> > device/console/1/ring-ref 8
> >   Aug  7 14:28:30 localhost xenstored:  D40.6        write     
> > device/console/1/port 10
> >   Aug  7 14:28:30 localhost xenstored:  D40.6        write     
> > device/console/1/type ioemu
> > 
> > â I think the last line is suspicious.
> 
> This was introduced by Stefano in 3.4 with 02e19f9c7cac (hvc_xen:
> implement multiconsole support).
> 
> Stefano, can you advise on whether it it safe to remove the write of the
> "type" key or whether we need to make it conditional on it being absent.
 
I think that the original idea was that since only ioemu backends (QEMU)
are capable of handling multiple consoles and the new xenstore based
console protocol, then the "type" had to be "ioemu".

I agree that the type key has no business being in the frontend
directory.
I also agree that the frontend shouldn't be writing it, since the
backend would have already been started anyway.

I think it would be OK to:

---
xen_hvc: no reason to write the type key on xenstore

The backend type is chosen by the toolstack. Regardless the frontend
should not care.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>

diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
index 636c9ba..b8491f5 100644
--- a/drivers/tty/hvc/hvc_xen.c
+++ b/drivers/tty/hvc/hvc_xen.c
@@ -402,9 +402,6 @@ static int xencons_connect_backend(struct xenbus_device 
*dev,
                            evtchn);
        if (ret)
                goto error_xenbus;
-       ret = xenbus_printf(xbt, dev->nodename, "type", "ioemu");
-       if (ret)
-               goto error_xenbus;
        ret = xenbus_transaction_end(xbt, 0);
        if (ret) {
                if (ret == -EAGAIN)

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel