Re: [PATCH v3 08/25] tools/xenstore: make hashtable key and value parameters const

[Juergen Gross <jgross@xxxxxxxx>]

On 25.07.23 18:08, Julien Grall wrote:
> Hi,
>
> On 24/07/2023 12:02, Juergen Gross wrote:
> > The key and value are never modified by hashtable code, so they should
> > be marked as const.
> You wrote this but...
>
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > ---
> > V3:
> > - make value const, too.
> > ---
> >   tools/xenstore/hashtable.c | 7 ++++---
> >   tools/xenstore/hashtable.h | 4 ++--
> >   2 files changed, 6 insertions(+), 5 deletions(-)
> >
> > diff --git a/tools/xenstore/hashtable.c b/tools/xenstore/hashtable.c
> > index 11f6bf8f15..670dc01003 100644
> > --- a/tools/xenstore/hashtable.c
> > +++ b/tools/xenstore/hashtable.c
> > @@ -11,7 +11,8 @@
> >   struct entry
> >   {
> > -    void *k, *v;
> > +    const void *k;
> > +    void *v;
>
> ... this is not const and ...
>
> >       unsigned int h;
> >       struct entry *next;
> >   };
> > @@ -140,7 +141,7 @@ static int hashtable_expand(struct hashtable *h)
> >       return 0;
> >   }
> > -int hashtable_add(struct hashtable *h, void *k, void *v)
> > +int hashtable_add(struct hashtable *h, const void *k, const void *v)
> >   {
> >       /* This method allows duplicate keys - but they shouldn't be used */
> >       unsigned int index;
> > @@ -164,7 +165,7 @@ int hashtable_add(struct hashtable *h, void *k, void *v)
> >       e->k = k;
> >       if (h->flags & HASHTABLE_FREE_KEY)
> >           talloc_steal(e, k);
> > -    e->v = v;
> > +    e->v = (void *)v;
> ... you cast-away the const here. I think this is a pretty bad idea.
>
> Can you clarify why you are doing like that?
The value is never changed by the hashtable code, but it might be changed by
e.g. a caller of hashtable_search() (see e.g. callers of find_domain_struct()).

Somewhere I need to cast the const away. I could do so in hashtable_search()
in case you prefer me to do so.


Juergen

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