RE: [PATCH v2 1/2] libxl: provide a mechanism to define a device 'safe remove' function...

["Durrant, Paul" <pdurrant@amazon.co.uk>]

> -----Original Message-----
> From: Roger Pau Monné <roger.pau@citrix.com>
> Sent: 15 September 2020 15:32
> To: Paul Durrant <paul@xen.org>
> Cc: xen-devel@lists.xenproject.org; Durrant, Paul <pdurrant@amazon.co.uk>; Ian Jackson
> <iwj@xenproject.org>; Wei Liu <wl@xen.org>; Anthony PERARD <anthony.perard@citrix.com>
> Subject: RE: [EXTERNAL] [PATCH v2 1/2] libxl: provide a mechanism to define a device 'safe remove'
> function...
> 
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> 
> 
> On Tue, Sep 15, 2020 at 03:10:06PM +0100, Paul Durrant wrote:
> > From: Paul Durrant <pdurrant@amazon.com>
> >
> > ... and use it to define libxl_device_disk_safe_remove().
> >
> > This patch builds on the existent macro magic by using a new value of the
> > 'force' field in in libxl__ao_device.
> > It is currently defined as an int but is used in a boolean manner where
> > 1 means the operation is forced and 0 means it is not (but is actually forced
> > after a 10s time-out). In adding a third value, this patch re-defines 'force'
> > as a struct type (libxl__force) with a single 'flag' field taking an
> > enumerated value:
> >
> > LIBXL__FORCE_AUTO - corresponding to the old 0 value
> > LIBXL__FORCE_ON   - corresponding to the old 1 value
> > LIBXL__FORCE_OFF  - the new value
> >
> > The LIBXL_DEFINE_DEVICE_REMOVE() macro is then modified to define the
> > libxl_device_<type>_remove() and libxl_device_<type>_destroy() functions,
> > setting LIBXL__FORCE_AUTO and LIBXL__FORCE_ON (respectively) in the
> > libxl__ao_device passed to libxl__initiate_device_generic_remove() and a
> > new macro, LIBXL_DEFINE_DEVICE_SAFE_REMOVE(), is defined that sets
> > LIBXL__FORCE_OFF instead. This macro is used to define the new
> > libxl_device_disk_safe_remove() function.
> >
> > Signed-off-by: Paul Durrant <pdurrant@amazon.com>
> 
> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
> 

Thanks.

> Just one nit.
> 
> > diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
> > index e16ae9630b..1fcf85c3e2 100644
> > --- a/tools/libxl/libxl_internal.h
> > +++ b/tools/libxl/libxl_internal.h
> > @@ -2730,12 +2730,20 @@ _hidden void libxl__prepare_ao_device(libxl__ao *ao, libxl__ao_device
> *aodev);
> >  /* generic callback for devices that only need to set ao_complete */
> >  _hidden void device_addrm_aocomplete(libxl__egc *egc, libxl__ao_device *aodev);
> >
> > +typedef struct {
> > +    enum {
> > +        LIBXL__FORCE_AUTO, /* Re-execute with FORCE_ON if op times out */
> > +        LIBXL__FORCE_ON,
> > +        LIBXL__FORCE_OFF,
> > +    } flag;
> > +} libxl__force;
> 
> Couldn't you just use the typedef against the union directly instead
> of wrapping it around a struct?

You mean s/union/enum?

I could have done that, but it helped find all the places where aodev->force is used and I liked the abstraction. I don't mind changing if there are strong opinions against it.

  Paul

> 
> Thanks, Roger.