> From: Hefty, Sean > Sent: Wednesday, June 10, 2015 4:32 PM > To: Hal Rosenstock; Wan, Kaike > Cc: linux-rdma@vger.kernel.org; Fleck, John; Weiny, Ira > Subject: RE: [PATCH v4 1/4] IB/netlink: Add defines for local service requests > through netlink > > > >>> +/* Local Service Reversible attribute */ struct > > >>> +rdma_nla_ls_reversible { > > >>> + __u32 reversible; > > >>> +}; > > >> > > >> Isn't __u8 sufficient for reversible ? > > > Certainly enough. However, reversible is __u32 in struct > > ib_user_path_rec and int in struct ib_sa_path_rec. > > > > OK; I hadn't double checked there. So it's "inherited" from those > > reversible definitions. > > I don't think we need to adhere to the sizes defined in other structures. I > agree with Hal's original comment. A __u8 here seems sufficient, unless we > want to introduce some bit fields.
There are two reasons why we should use __u32 here: 1. Easy to convert from struct ib_sa_path_rec (the input) to netlink attribute: nla_put(skb, LS_NLA_TYPE_REVERSIBLE, sizeof(sa_rec->reversible), &sa_rec->reversible); Instead of: __u8 tmp; tmp = (__u8)sa_rec->reversible; nla_put(skb, , LS_NLA_TYPE_REVERSIBLE, sizeof(tmp), &tmp); 2. Most importantly, sa_rec->reversible is define as type "int", but it really is "__be32" (big-endian), as proven below: path rec: len 64 : 00 00 00 00 00 00 00 00 fe 80 00 00 00 00 00 00 00 11 75 00 00 78 ad 92 fe 80 00 00 00 00 00 00 00 11 75 00 00 78 a4 24 00 07 00 03 00 00 00 00 00 80 ff ff 00 00 84 87 92 00 00 00 00 00 00 00 sa path_rec: len 88 : 00 00 00 00 00 00 00 00 fe 80 00 00 00 00 00 00 00 11 75 00 00 78 ad 92 fe 80 00 00 00 00 00 00 00 11 75 00 00 78 a4 24 00 07 00 03 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01 00 00 ff ff 00 00 00 02 04 02 07 02 12 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff sa path_rec reversible 0x1000000 The path rec is the pathrecord returned from ibacm in MAD wire format (dumped in sa_query.c). The byte "0x80" before "ff ff" (the third row) is reversible_numpath field (reversible bit 7: 1). The sa_path_rec is the struct ib_sa_path_rec dumped in cma_query_handler() in cma.c (rdma_cm) when the query callback is invoked. The data "00 00 00 01" (the last four bytes of the third row) is the field ib_sa_path_rec->reversible (there are some alignment padding for fields before it). Again the same field is dumped in user-friendly version as 0x1000000 (or 0x01000000), indicating that it is in big-endian format. This test was run on x86_64 machines with Opensm as the SM/SA. I stumped across this during previous patch tests where ibacm returned struct ib_user_path_rec as the response. In that test, I had to manually convert struct ibv_path_record into ib_user_path_rec. Then in ib_sa, I had to convert from struct ib_user_path_rec to struct ib_sa_path_rec. If I set ib_user_path_rec->reversible = 1, then the returned result failed rping; If I set ib_user_path_rec->reversible = 0x01000000, then rping successfully connected to the destination. I also used ib_pack() and ib_unpack() to convert between struct ib_sa_path_rec and pathrecord in MAD wire format (struct ibv_path_record) and compared the result with that from SA. If ib_sa_path_rec->reversible = 1, the ibv_path_record->reversible_numpath=0x00; if ib_sa_path_rec->reversible=0x01000000, then ibv_path_record->reversible_numpath=0x80. As a result, I think that the following code is incorrect in cma_query_ib_route() (cma.c): path_rec.reversible = 1; I am surprised that it still works to query SA with IB_SA_PATH_REC_REVERSIBLE bit set in comp_mask. By the way, of the three callers of ib_sa_path_rec_get(), this is the only place that ib_sa_path_rec.reversible is set. That is why we should use __u32 as the attribute data type for reversible. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html