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[204.195.112.43]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2edb6d906e4sm10414035ad.40.2026.11.10.07.19.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 10 Nov 2026 07:19:31 -0800 (PST) Date: Tue, 10 Nov 2026 07:19:28 -0800 From: Stephen Hemminger To: Hangbin Liu Cc: netdev@vger.kernel.org, dsahern@kernel.org, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Kuniyuki Iwashima , Ido Schimmel , Sabrina Dubroca , Andrea Parri , Stanislav Fomichev , Nikolaos Gkarlis , Willem de Bruijn , open list Subject: Re: [PATCH 1/3] rtnetlink: return EMSGSIZE when first dump entry does not fit Message-ID: <20261110071928.6e8aebd7@phoenix.local> In-Reply-To: References: <20261109012115.11898-1-stephen@networkplumber.org> <20261109012115.11898-2-stephen@networkplumber.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 10 Nov 2026 16:27:41 +0800 Hangbin Liu wrote: > Hi Stephen, > On Sun, Nov 08, 2026 at 05:13:12PM -0800, Stephen Hemminger wrote: > > If a route entry is too large for the dump skb, the dump is silently > > truncated and no error is returned. > > > > For handlers with RTNL_FLAG_DUMP_SPLIT_NLM_DONE, rtnl_dumpit() drops > > -EMSGSIZE and returns skb->len. With an empty skb this is 0, so the > > dump ends with NLMSG_DONE and status 0, and the remaining entries are > > lost. > > > > The first dump skb is allocated from __netlink_dump_start() while > > max_recvmsg_len is still 0, so it is only NLMSG_GOODSIZE. On a 4K page > > kernel that is under 4000 bytes, and a 500 way multipath route does not > > fit: > > > > ip link add dummy0 type dummy > > ip link set dummy0 up > > ip route add 198.51.100.0/24 table 100 \ > > $(for i in $(seq 500); do echo -n "nexthop dev dummy0 "; done) > > ip route show table 100 > > > > The dump prints nothing and exits 0, although "ip route get > > 198.51.100.1 table 100" still shows the route. > > One question. AFAIK, `ip route get` doesn't support "table" parameter. No? > > Thanks > Hangbin Your right AI is wrong in the commit message. A way to use get is to add a rule. # ip rule add to 198.51.100.0/24 lookup 100 # ip route get 198.51.100.1 198.51.100.1 dev dummy0 table 100 src 192.168.50.131 uid 0 cache But best to just drop the incorrect wording there.