Re: [Xen-devel] [PATCH] libxl: handle null lists in libxl_string_list_length

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Sat, 2013-09-28 at 00:20 +1200, Matthew Daley wrote:
> On Sat, Sep 28, 2013 at 12:08 AM, Boris Ostrovsky
> <boris.ostrovsky@xxxxxxxxxx> wrote:
> >
> > ----- mattjd@xxxxxxxxx wrote:
> >
> >> After commit b0be2b12 ("libxl: fix libxl_string_list_length and its
> >> only
> >> caller") libxl_string_list_length no longer handles null (empty)
> >> lists. Fix
> >> so they are handled, returning length 0.
> >>
> >> While at it, remove the unneccessary undereferenced null pointer
> >> check
> >
> > Are you sure this check should be removed? This routine can be called
> > from anywhere (at least within libxl it seems) and one day someone will
> > call it with NULL argument.
> >
> > I'd probably leave this check in.
> 
> I would argue that any such invocation would be an error by the caller
> and should fail noisily, similar to how passing NULL into strlen
> should not return 0. libxl_{string,key_value}_list_dispose similarly
> assumes non-NULL pointers, FWIW.
> 
> Ian C., do you have an opinion either way?

I think a zero length list is a bit different to a NULL string and
should return 0.

But libxl_string_list is already char** so this function is taking
char***. The check for char *** == NULL, which is being removed, appears
to be unnecessary. A zero length list would be char ** == NULL, which
should be handled (and is I think?). char * == NULL would be a "" entry
in the string list.

Confused? I know I am ;-)

Ian.


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