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([2001:ee0:4f0e:fb30:1f60:cc25:9268:94fb]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-749b5e21799sm2122923b3a.51.2025.06.24.07.58.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Jun 2025 07:58:55 -0700 (PDT) Message-ID: Date: Tue, 24 Jun 2025 21:58:47 +0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net v2 2/2] virtio-net: xsk: rx: move the xdp->data adjustment to buf_to_xdp() To: Paolo Abeni , netdev@vger.kernel.org Cc: "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, bpf@vger.kernel.org References: <20250621144952.32469-1-minhquangbui99@gmail.com> <20250621144952.32469-3-minhquangbui99@gmail.com> Content-Language: en-US From: Bui Quang Minh In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 6/24/25 17:17, Paolo Abeni wrote: > On 6/21/25 4:49 PM, Bui Quang Minh wrote: >> This commit does not do any functional changes. It moves xdp->data >> adjustment for buffer other than first buffer to buf_to_xdp() helper so >> that the xdp_buff adjustment does not scatter over different functions. >> >> Signed-off-by: Bui Quang Minh >> --- >> drivers/net/virtio_net.c | 16 ++++++++++++++-- >> 1 file changed, 14 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >> index 1eb237cd5d0b..4e942ea1bfa3 100644 >> --- a/drivers/net/virtio_net.c >> +++ b/drivers/net/virtio_net.c >> @@ -1159,7 +1159,19 @@ static struct xdp_buff *buf_to_xdp(struct virtnet_info *vi, >> return NULL; >> } >> >> - xsk_buff_set_size(xdp, len); >> + if (first_buf) { >> + xsk_buff_set_size(xdp, len); >> + } else { >> + /* This is the same as xsk_buff_set_size but with the adjusted >> + * xdp->data. >> + */ >> + xdp->data = xdp->data_hard_start + XDP_PACKET_HEADROOM; >> + xdp->data -= vi->hdr_len; >> + xdp->data_meta = xdp->data; >> + xdp->data_end = xdp->data + len; >> + xdp->flags = 0; >> + } >> + >> xsk_buff_dma_sync_for_cpu(xdp); >> >> return xdp; >> @@ -1284,7 +1296,7 @@ static int xsk_append_merge_buffer(struct virtnet_info *vi, >> goto err; >> } >> >> - memcpy(buf, xdp->data - vi->hdr_len, len); >> + memcpy(buf, xdp->data, len); >> >> xsk_buff_free(xdp); >> > I'm unsure if this change is in the right direction because it almost > open-code the existing xsk_buff_set_size() helper - any changes there > should be reflected here, too. > > Also AFAICS xdp->data will now carry a different value, and I guess such > change is user-visible from the attached xdp program. The commit message > should at least mentions such fact. The else path in buf_to_xdp is only triggered when it's called in xsk_append_merge_buffer. That's also the reason of the memcpy line change in xsk_append_merge_buffer. xsk_append_merge_buffer will allocate frag and copy xdp_buff's data to that frag. Previously, after buf_to_xdp, the xdp->data does not point to correct place yet so when memcpy, we need to copy from xdp->data - vi->hdr_len. With this change, we will adjust xdp->data = xdp->data - vi->hdr_len right in buf_to_xdp and also adjust other fields (xdp->data_end) to the correct place too. So I don't think there is a functional change in this commit. Thanks, Quang Minh.