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([2620:10d:c090:500::5:8b4]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-b31f1241f20sm8726707a12.45.2025.06.23.14.45.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Jun 2025 14:45:37 -0700 (PDT) Message-ID: <59e7ca59c4c0ac455aa05c7ebd0ecd67871a5b47.camel@gmail.com> Subject: Re: [PATCH bpf-next 1/2] bpf: add bpf_dynptr_memset() kfunc From: Eduard Zingerman To: Andrii Nakryiko Cc: Ihor Solodrai , Mykyta Yatsenko , andrii@kernel.org, bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, mykolal@fb.com, kernel-team@meta.com Date: Mon, 23 Jun 2025 14:45:35 -0700 In-Reply-To: References: <20250618223310.3684760-1-isolodrai@meta.com> <45390c6c-bd2a-4962-8222-1ad346f9908c@linux.dev> <7852f30ba177dc5b811bb0840ca0f301df2a8b58.camel@gmail.com> <7e7e4056-e2b8-41a5-a6b2-a2fbe0a94f4c@linux.dev> <50c2f252620107b6fa6642e281a91db444b032c5.camel@gmail.com> <51cbadb3cabbb0b2479e5087618e1015c25b4f26.camel@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-1.fc42) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2025-06-23 at 14:38 -0700, Andrii Nakryiko wrote: > On Thu, Jun 19, 2025 at 11:17=E2=80=AFAM Eduard Zingerman wrote: > >=20 > > On Thu, 2025-06-19 at 11:13 -0700, Eduard Zingerman wrote: > >=20 > > [...] > >=20 > > > Also, what's the plan if you'd like to memset only a fragment of the > > > memory pointed-to by dynptr? > >=20 > > Oh, I see, there is bpf_dynptr_adjust(), sorry for the noise. > >=20 >=20 > Even though we do have bpf_dynptr_adjust() for maximum generality and > flexibility, for most dynptr-based APIs we try to pass also additional > offset into dynptr to avoid unnecessary overhead. So it's not a bad > idea to add this to bpf_memset(), IMO. >=20 > bpf_memset(struct bpf_dynptr *dptr, u32 off, u8 val, u32 n) ? >=20 > a bit unfortunate that we have 3 integers that you need to be careful > to not swap accidentally, but even with just val and n you'd have to > be careful. For other APIs we normally have offset to follow dynptr > pointer, so hopefully this arrangement won't that surprising. >=20 > Thoughts? Unfortunate indeed. The off and n being separated looks weird, tbh. For dynptr funcs we actually have "dptr, off, size" everywhere, maybe do the same here?