> From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Dumitrescu, Cristian > Sent: Monday, April 9, 2018 4:59 PM > To: Stephen Hemminger <step...@networkplumber.org>; Singh, Jasvinder > <jasvinder.si...@intel.com>; Richardson, Bruce <bruce.richard...@intel.com> > Cc: dev@dpdk.org > Subject: Re: [dpdk-dev] [PATCH] table: fix build error with gcc 8 > > > > > -----Original Message----- > > From: Stephen Hemminger [mailto:step...@networkplumber.org] > > Sent: Monday, April 9, 2018 4:10 PM > > To: Singh, Jasvinder <jasvinder.si...@intel.com> > > Cc: dev@dpdk.org; Dumitrescu, Cristian <cristian.dumitre...@intel.com> > > Subject: Re: [dpdk-dev] [PATCH] table: fix build error with gcc 8 > > > > On Mon, 9 Apr 2018 13:49:48 +0100 > > Jasvinder Singh <jasvinder.si...@intel.com> wrote: > > > > > Fix build error with gcc 8.0 due to cast between function types. > > > Fixes: 5a80bf0ae613 ("table: add cuckoo hash") > > > > > > Signed-off-by: Jasvinder Singh <jasvinder.si...@intel.com> > > > --- > > > lib/librte_table/rte_table_hash_cuckoo.c | 4 +++- > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > diff --git a/lib/librte_table/rte_table_hash_cuckoo.c > > b/lib/librte_table/rte_table_hash_cuckoo.c > > > index dcb4fe9..f7eae27 100644 > > > --- a/lib/librte_table/rte_table_hash_cuckoo.c > > > +++ b/lib/librte_table/rte_table_hash_cuckoo.c > > > @@ -103,11 +103,13 @@ rte_table_hash_cuckoo_create(void *params, > > > return NULL; > > > } > > > > > > + void *hash_func = p->f_hash; > > > + > > > /* Create cuckoo hash table */ > > > struct rte_hash_parameters hash_cuckoo_params = { > > > .entries = p->n_keys, > > > .key_len = p->key_size, > > > - .hash_func = (rte_hash_function)(p->f_hash), > > > + .hash_func = (rte_hash_function) hash_func, > > > .hash_func_init_val = p->seed, > > > .socket_id = socket_id, > > > .name = p->name > > > > This is just tricking the compiler into not complaining. > > I would really rather see the two hash functions made the same. > > (Adding Bruce as well to consolidate all conversations in a single thread.) > > What we want to do here is be able to use the librte_hash under the same API > as the several hash table flavors implemented in librte_table. > > Both of these libraries allow configuring the hash function per each hash > table instance. Problem is: hash function in librte_hash has only 3 parameters > (no key mask), while hash function in librte_table has 4 parameters (includes > key mask). The key mask helps a lot for practical protocol implementations by > avoiding key copy & pre-process on lookup. > > So then: how to plug in librte_hash under the same API as the suite of hash > tables in librte_table? We don't want to re-implement cuckoo hash from > librte_hash, we simply want to invoke it as a low-level primitive, similarly > to how the LPM and ACL tables are plugged into librte_table. > > Solution is: as an exception, pass a 3-parameter hash function to cuckoo hash > flavor under the librte_table. Maybe this should be documented better. This > currently triggers a build warning with gcc 8, which is easy to fix, hence > this trivial patch. > > Ideally, for every 3-parameter hash function, I would like to generate the > corresponding 4-parameter hash function on-the-fly, but unfortunately this is > not what C language can do. > > Of course, IMO the best solution is to add key mask support to librte_hash.
Looking at the previous discussion I see the following as a possible solution; Given the current code looks broken it should be fixed in this release. Given the actual code fix is an API / ABI break (depending on solution) it cannot be merged official in this release. We have a NEXT_ABI macro - it allows us to break API/ABI conditionally at compile time. With the above 3 points, I think the best solution is to correctly fix the problem that GCC 8 is identifying, and putting that new API inside the NEXT_ macros. In this case, we can preserve backwards (buggy) behavior if required, and provide correct (but API/ABI breaking) code as well. This is a tough decision - particularly for distros - what do they package? Given the current code, I don't see a better solution - but I hope I'm wrong :)
