[Xen-devel] RFC: PV vfb's and the handling of global vnc options

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

So I had a user report that he couldn't get the vnclisten option to
work.  It turns out he was using a PV guest, and had the following in
his config file:

vfb=[ 'type=vnc' ]
vnclisten='0.0.0.0'

After digging around in the code, it turns out that the following is
accepted for PV guests:

vnc=1
vnclisten='0.0.0.0'

...on the condition that there be *no* vfb option.  If you set the vfb
option, then the top-level vnc entries are completely ignored.

The following also works (as one might expect):

vfb=[ 'type=vnc,vnclisten=0.0.0.0' ]

The man page is a bit unclear here; it says:

If "Emulated VGA Graphics Device" options are used in a PV guest
configuration, xl will pick up vnc, vnclisten, vncpasswd, vncdisplay,
vncunused, sdl, opengl and keymap to construct paravirtual framebuffer
device for the guest.

I see two options:

1. Make vfb take defaults from the top-level vnc options

2. Clarify the man page to make it clear that top-level vnc options
will only have an effect if no vfb is specified.

I'm of two minds which one is best.  At the moment I'm leaning towards
#2, possibly adding a warning if it finds both vfb and toplevel vnc
options, saying that it's ignoring the second.

Any opinions?

 -George

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