Re: [Xen-devel] [PATCH] docs/misc: document PV control/feature keys for laptop/slate mode

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 30 Mar 2017, Paul Durrant wrote:
> On 30 March 2017, at 18:49, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote:
> >On Thu, 30 Mar 2017, Paul Durrant wrote:
> >> Commit 4c8153d9 "add ACPI device for Windows laptop/slate mode switch"
> >> added code to provide an 'laptop/slate mode' ACPI device to guests.
> >>
> >> When present this device is used by Microsoft Windows to bind a HID
> >> driver which controls whether the Windows desktop appearance is optimized
> >> for laptop/desktop or slate/tablet PCs. The mechanism for switching
> >> between modes is to open a handle to this driver and write a byte of
> >> arbitrary data.
> >>
> >> This patch documents xenstore keys such that a PV agent running in a
> >> Windows guest can advertise the capability to, and receive instruction
> >> from, a toolstack to cause such a mode switch.
> >>
> >> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> >> ---
> >> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> >> Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> >> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> >> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> >> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> >> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> >> Cc: Tim Deegan <tim@xxxxxxx>
> >> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> >> ---
> >>  docs/misc/xenstore-paths.markdown | 15 +++++++++++++++
> >>  1 file changed, 15 insertions(+)
> >>
> >> diff --git a/docs/misc/xenstore-paths.markdown 
> >> b/docs/misc/xenstore-paths.markdown
> >> index 5d89ed8..6c80a9e 100644
> >> --- a/docs/misc/xenstore-paths.markdown
> >> +++ b/docs/misc/xenstore-paths.markdown
> >> @@ -435,6 +435,21 @@ XS_RESET_WATCHES xenstore message. See
> >>  [xen/include/public/io/xs\_wire.h][XSWIRE] for the XenStore wire
> >>  protocol definition.
> >> 
> >> +#### ~/control/laptop-slate-mode = (""|"laptop"|"slate") [w]
> >> +
> >> +This is the PV laptop/slate mode control node. If the toolstack has
> >> +provisioned a guest with the ACPI laptop/slate mode device then it
> >> +can write the desired mode here to cause the guest to switch modes if
> >> +necessary. The guest acknowledges a request by writing the empty
> >> +string back to the control node.
> >> +
> >> +#### ~/control/feature-laptop-slate-mode = (""|"0"|"1") [w]
> >> +
> >> +This may be initialized to "" by the toolstack and may then be set
> >> +to 0 or 1 by a guest to indicate whether it is capable or incapable,
> >> +respectively, of responding to a mode value written to
> >> +~/control/laptop-slate-mode.
> >Usually, this is done by having the guest drivers write something like:
> >feature-laptop-slate-mode
> >to xenstore. The lack of the feature-* means no support is available.
> >In fact, how is this supposed to work with old guest PV drivers that
> >don't know about ~/control/feature-laptop-slate-mode? There won't be
> >anybody to write "0" there, right?
> 
> The toolstack has to write this first because the parent control key is read 
> only to the guest.
> Old guests will not write 0 so the toolstack does not know whether the guest 
> can handle a command written to control/laptop-slate-mode. It has to apply 
> some form of timeout in
> that case. This is exactly the same as with any of the shutdown features.

All right, I had not read the shutdown protocol before, so this struck
me as odd (compared to PV frontends/backends). If I were to write this,
I would avoid the possibility to end up in uncertain state like "".
However, it is up to you :)


> >>  ### Domain Controlled Paths
> >> 
> >>  #### ~/data/* [w]
> >> --
> >> 2.1.4
> >>
> >
> 
> 
>

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