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Re: [Xen-devel] [PATCH RFC] xen/console: buffer and show origin of guest PV writes

On 08/13/2013 12:52 PM, Jan Beulich wrote:
On 13.08.13 at 18:34, Daniel De Graaf <dgdegra@xxxxxxxxxxxxx> wrote:
1. HVM guests' output is currently limited to printable characters; do
we want to implement the same restriction on PV guests?

Would seem to make sense.

It seems only dom0 will try to use control characters under normal
conditions, so this shouldn't cause any issues (hopefully).

2. The prefix on the serial console for PV output is "(XEN) d5: ", while
HVM output is still "(XEN) HVM5: "; should these be made consistent?

Uniformly using e.g. "(Dom%d) " instead of "(XEN) " for domain output
might be best?

I think this makes sense as a way to distinguish guest output from Xen
output regarding a guest. This will probably require introducing a
vprintk-ish function to add the guest domid argument.

The original version of this patch used "(%d) ", but I think "(d%d) " or
"(dom%d) " may end up being clearer.

3. Should we change to allowing console output by default, since it is
now controlled by log levels?

I don't think we should, not the least because guest output doesn't
really specify a log level, and default log level messages make it
through with default options.

The existing HVM guest output is done with XENLOG_G_DEBUG, which was
copied for the PV guest output. The default value of guest_loglvl on a
debug build includes this output, but on a non-debug build hides it.

Will have to look at the patch itself later, but you should have Cc-ed
Keir in any case (as he will eventually need to ack it).


Ah, for some reason I didn't have him on the original list. I have added
him to this message to highlight the thread and will fix that on a resend.

Daniel De Graaf
National Security Agency

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