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[185.107.14.3]) by smtp.gmail.com with ESMTPSA id d4sm5240621wrz.35.2021.08.18.01.54.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 18 Aug 2021 01:54:57 -0700 (PDT) From: Jesper Dangaard Brouer X-Google-Original-From: Jesper Dangaard Brouer Cc: brouer@redhat.com, Jithu Joseph Subject: Re: [RFC bpf-next 5/5] samples/bpf/xdpsock_user.c: Launchtime/TXTIME API usage To: Kishen Maloor , bpf@vger.kernel.org, netdev@vger.kernel.org, hawk@kernel.org, magnus.karlsson@intel.com, =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= References: <20210803171006.13915-1-kishen.maloor@intel.com> <20210803171006.13915-6-kishen.maloor@intel.com> Message-ID: <4ea898db-563c-851b-c3da-9389abcb83ac@redhat.com> Date: Wed, 18 Aug 2021 10:54:55 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210803171006.13915-6-kishen.maloor@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 03/08/2021 19.10, Kishen Maloor wrote: > diff --git a/samples/bpf/xdpsock_user.c b/samples/bpf/xdpsock_user.c > index 3fd2f6a0d1eb..a0fd3d5414ba 100644 > --- a/samples/bpf/xdpsock_user.c > +++ b/samples/bpf/xdpsock_user.c [...] > @@ -741,6 +745,8 @@ static inline u16 udp_csum(u32 saddr, u32 daddr, u32 len, > > #define ETH_FCS_SIZE 4 > > +#define MD_SIZE (sizeof(struct xdp_user_tx_metadata)) > + > #define PKT_HDR_SIZE (sizeof(struct ethhdr) + sizeof(struct iphdr) + \ > sizeof(struct udphdr)) > > @@ -798,8 +804,10 @@ static void gen_eth_hdr_data(void) > > static void gen_eth_frame(struct xsk_umem_info *umem, u64 addr) > { > - memcpy(xsk_umem__get_data(umem->buffer, addr), pkt_data, > - PKT_SIZE); > + if (opt_launch_time) > + memcpy(xsk_umem__get_data(umem->buffer, addr) + MD_SIZE, pkt_data, PKT_SIZE); > + else > + memcpy(xsk_umem__get_data(umem->buffer, addr), pkt_data, PKT_SIZE); > } > I imagined that AF_XDP 'addr' would still point to the start of the packet data, and that metadata area was access via a negative offset from 'addr'. Maybe I misunderstood the code, but it looks like 'addr' (xsk_umem__get_data(umem->buffer, addr)) points to metadata area, is this correct? (and to skip this the code does + MD_SIZE, before memcpy) One problem/challenge with AF_XDP is that we don't have room in struct xdp_desc to store info on the size of the metadata area. Bjørn came up with the idea of having btf_id as last member (access able via minus 4 bytes), as this tells the kernel the size of metadata area. Maybe you have come up with a better solution? (of making the metadata area size dynamic) --Jesper