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Thu, 12 Nov 2026 00:32:44 -0800 (PST) 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 References: <20261110102039.1002605-1-bjorn@kernel.org> <20261110102039.1002605-2-bjorn@kernel.org> In-Reply-To: <20261110102039.1002605-2-bjorn@kernel.org> From: saeed bishara Date: Thu, 12 Nov 2026 10:32:32 +0200 X-Gm-Features: AclHuK_JmHtMGasdG1MlcgZSR9JInf5KlnPcivwlvNEZTX0IPHWZAk1Q01MwQ2M Message-ID: Subject: Re: [PATCH net-next v1 01/11] net: Get skb fragment addresses through netmem To: =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= Cc: Magnus Karlsson , Maciej Fijalkowski , Stanislav Fomichev , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Jonathan Corbet , Shuah Khan , Randy Dunlap , Alexander Duyck , kernel-team@meta.com, Andrew Lunn , Jesper Dangaard Brouer , Ilias Apalodimas , Alexei Starovoitov , Daniel Borkmann , John Fastabend , Pavel Begunkov , Jens Axboe , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , netdev@vger.kernel.org, bpf@vger.kernel.org, io-uring@vger.kernel.org, Mina Almasry , "Mike Marciniszyn (Meta)" , Weiming Shi , Nikolay Aleksandrov , David Wei , Alexander Lobakin , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Stuart Clark Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, Nov 10, 2026 at 12:27=E2=80=AFPM Bj=C3=B6rn T=C3=B6pel wrote: > > skb_frag_address() goes through struct page, so a net_iov never has an > address. Only unreadable memory should lack one: XDP and BPF read > fragments through this helper, and AF_XDP UMEM will back readable > net_iovs. netmem_address() also returns NULL, not a bogus pointer, for > an unmapped highmem page. Does this mean that skb_frag_address_safe() is practically identical to skb_frag_address()? I assume highmem page is the only case where non niov page isn't mapped. > > * > - * Returns: the address of the data within @frag. The page must already > - * be mapped. > + * Returns: the address of the data within @frag, or %NULL if the CPU ca= nnot > + * read it. "CPU cannot read" isn't accurate, I assume that in iouring case the buffer is mapped to userspace. > */