Re: [dpdk-dev] [RFC] hash/lpm: return NULL if the object exists

[Bruce Richardson <bruce.richardson@intel.com>]

On Fri, Mar 25, 2016 at 11:32:47AM +0100, Olivier Matz wrote:
> Hi Bruce,
> 
> On 03/15/2016 01:25 PM, Olivier Matz wrote:
> > Seen by trying to fix the func_reentrancy autotest. The test
> > was doing the following on several cores in parallel:
> > 
> >   name = "common_name";
> >   do several times {
> >       obj = allocate_an_object(name)   // obj = ring, mempool, hash, lpm, ...
> >       if (obj == NULL && lookup(name) == NULL)
> >           return TEST_FAIL;
> >   }
> > 
> > Issues:
> > 
> > 1/ rings, mempools, hashs API are not coherent
> >    rings and mempool return NULL if the object does not exist
> >    hash and lpm return an object that was allocated allocated if
> >    it already was allocated
> > 
> > 2/ The hash/lpm API looks dangerous: when an object is returned,
> >    the user does not know if it should be freed or not (no refcnt)
> > 
> > 3/ There are some possible race conditions in cuckoo_hash as the
> >    lock is not held in rte_hash_create(). We could find some cases
> >    where NULL is returned when the object already exists (ex: when
> >    rte_ring_create() fails).
> > 
> > This patch tries to rationalize the APIs of lpm and hash.
> > 
> > Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
> 
> Sorry, I forgot to CC you in the first mail. Do you have any opinion
> about this rfc patch?
> 
> Thanks,
> Olivier
Hi Olivier,

the idea looks good, since an object already existing is an error condition on
create. One small change to the libs I'd suggest is to set rte_errno to 
EEXIST before exit, so that the error reason is known to the app.

Regards,
/Bruce