Re: [Xen-devel] [PATCH RFC V2 06/10] libxl_json: allow basic JSON type objects generation

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2014-04-23 at 11:15 +0100, Wei Liu wrote:
> On Tue, Apr 22, 2014 at 04:22:20PM +0100, Ian Campbell wrote:
> > On Thu, 2014-04-17 at 12:13 +0100, Wei Liu wrote:
> > > The original logic is that basic JSON types (number, string and null)
> > > must be an element of JSON map or array. This assumption doesn't hold
> > > true anymore when we need to return basic JSON types.
> > > 
> > > Returning basic JSON types is required for parsing number, string and
> > > null objects back into libxl__json_object.
> > > 
> > > Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> > > ---
> > >  tools/libxl/libxl_json.c |   40 ++++++++++++++++++++++++++++++++--------
> > >  1 file changed, 32 insertions(+), 8 deletions(-)
> > > 
> > > diff --git a/tools/libxl/libxl_json.c b/tools/libxl/libxl_json.c
> > > index e2d5dbe..6b2946d 100644
> > > --- a/tools/libxl/libxl_json.c
> > > +++ b/tools/libxl/libxl_json.c
> > > @@ -629,8 +629,14 @@ static int json_callback_null(void *opaque)
> > >  
> > >      obj = libxl__json_object_alloc(ctx->gc, JSON_NULL);
> > >  
> > > -    if (libxl__json_object_append_to(ctx->gc, obj, ctx->current) == -1) {
> > > -        return 0;
> > > +    if (ctx->current) {
> > > +        if (libxl__json_object_append_to(ctx->gc, obj, ctx->current) == 
> > > -1) {
> > > +            return 0;
> > > +        }
> > > +    }
> > > +
> > > +    if (ctx->head == NULL) {
> > > +        ctx->head = obj;
> > 
> > It seems that this pattern is now pretty much universal on all callers
> > of libxl__json_object_append_to. Perhaps much of this functionality
> > should be pushed down into the helper (which might now need to take ctx
> > and not ctx->current).
> > 
> 
> But not every new allocated object needs to be appended to some other
> object, so pushing that functionality to libxl__json_object_append_to is
> not correct.

???

AFAICT every call of libxl__json_object_append_to after this patch now
has exactly the same boiler plate around it. The need append or not is a
property of the current context (in a map) not of the current object
being handled.

> > The existing callers seem to all set ctx->current too, just before the
> > ctx->head == NULL check. Why don't these versions need that too?
> > 
> 
> Because "current" is used to reference to "the array or map that we're
> currently in", so that we can call
> libxl__json_object_append_to(current).
> 
> Not very useful to set "current" for basic types because no other
> objects can be appended to them.

OK, I think this bit could be left in the relevant callers rather than
being made generic. Or it could be a parameter to object_append_to (e.g.
bool_t is_a_container, or pass the JSON_*).

Ian.


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