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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

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.

> 
> 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.

Wei.

> Ian

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