Re: [dpdk-dev] [PATCH 3/4] hash: fix rw concurrency while moving keys

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

> > > >
> > > >Reader-writer concurrency issue, caused by moving the keys to their
> > > >alternative locations during key insert, is solved by introducing a
> > > >global counter(tbl_chng_cnt) indicating a change in table.
> 
> <snip>
> 
> > > > /**
> > > >@@ -200,7 +200,7 @@ rte_hash_add_key_with_hash_data(const struct
> > > >rte_hash
> > *h, const void *key,
> > > >  *     array of user data. This value is unique for this key.
> > > >  */
> > > > int32_t
> > > >-rte_hash_add_key(const struct rte_hash *h, const void *key);
> > > >+rte_hash_add_key(struct rte_hash *h, const void *key);
> > > >
> > > > /**
> > > >  * Add a key to an existing hash table.
> > > >@@ -222,7 +222,7 @@ rte_hash_add_key(const struct rte_hash *h,
> > > >const void
> > *key);
> > > >  *     array of user data. This value is unique for this key.
> > > >  */
> > > > int32_t
> > > >-rte_hash_add_key_with_hash(const struct rte_hash *h, const void
> > > >*key,
> > hash_sig_t sig);
> > > >+rte_hash_add_key_with_hash(struct rte_hash *h, const void *key,
> > hash_sig_t sig);
> > > >
> > > > /
> > >
> > > I think the above changes will break ABI by changing the parameter type?
> > Other people may know better on this.
> >
> > Just removing a const should not change the ABI, I believe, since the
> > const is just advisory hint to the compiler. Actual parameter size and
> > count remains unchanged so I don't believe there is an issue.
> > [ABI experts, please correct me if I'm wrong on this]
> 
> 
> [Certainly no ABI expert, but...]
> 
> I think this is an API break, not ABI break.
> 
> Given application code as follows, it will fail to compile - even though running
> the new code as a .so wouldn't cause any issues (AFAIK).
> 
> void do_hash_stuff(const struct rte_hash *h, ...) {
>     /* parameter passed in is const, but updated function prototype is non-
> const */
>     rte_hash_add_key_with_hash(h, ...);
> }
> 
> This means that we can't recompile apps against latest patch without
> application code changes, if the app was passing a const rte_hash struct as
> the first parameter.
> 
Agree. Do we need to do anything for this?

> 
> -Harry