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[83.57.175.68]) by smtp.gmail.com with ESMTPSA id n5sm5353733edw.7.2021.02.26.02.29.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 26 Feb 2021 02:29:09 -0800 (PST) Subject: Re: [RFC PATCH 1/3] net: Pad short frames to minimum size (60 bytes) To: Bin Meng , Jason Wang , Peter Maydell , qemu-devel@nongnu.org References: <1614333786-74258-1-git-send-email-bmeng.cn@gmail.com> <1614333786-74258-2-git-send-email-bmeng.cn@gmail.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: Date: Fri, 26 Feb 2021 11:29:07 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <1614333786-74258-2-git-send-email-bmeng.cn@gmail.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.435, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Bin Meng Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2/26/21 11:03 AM, Bin Meng wrote: > From: Bin Meng > > The minimum Ethernet frame length is 60 bytes, and we should pad > frames whose length is smaller to the minimum size. > > This commit fixes the issue as seen with various ethernet models, > that ARP requests get dropped, preventing the guest from becoming > visible on the network. Is it also used in commit 18995b9808d ("Send a RARP packet after migration.")? > The following 2 commits that attempted to workaround this issue > in e1000 and vmxenet3 before, should be reverted. > > commit 78aeb23eded2 ("e1000: Pad short frames to minimum size (60 bytes)") > commit 40a87c6c9b11 ("vmxnet3: Pad short frames to minimum size (60 bytes)") > > Signed-off-by: Bin Meng > --- > > net/net.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/net/net.c b/net/net.c > index b038370..34004da 100644 > --- a/net/net.c > +++ b/net/net.c > @@ -638,6 +638,7 @@ static ssize_t qemu_send_packet_async_with_flags(NetClientState *sender, > NetPacketSent *sent_cb) > { > NetQueue *queue; > + uint8_t min_buf[60]; Can you add a definition instead of a magic value? Maybe ETH_FRAME_MIN_LEN in "net/eth.h"? > int ret; > > #ifdef DEBUG_NET > @@ -649,6 +650,14 @@ static ssize_t qemu_send_packet_async_with_flags(NetClientState *sender, > return size; > } > > + /* Pad to minimum Ethernet frame length */ > + if (size < sizeof(min_buf)) { > + memcpy(min_buf, buf, size); > + memset(&min_buf[size], 0, sizeof(min_buf) - size); > + buf = min_buf; > + size = sizeof(min_buf); > + } > + > /* Let filters handle the packet first */ > ret = filter_receive(sender, NET_FILTER_DIRECTION_TX, > sender, flags, buf, size, sent_cb); >