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AJvYcCWULAMkaFy2ykpLqj6NBfyUmSrhcS/ngb17vJDFkDSZKWwEbne4+HYFWEqdF1tt82FT6hEjPkqVplcrwd0=@vger.kernel.org X-Gm-Message-State: AOJu0YynCVoJfnHC1yGFeuc7emYHcWjv+5D07C75LjrHCA8AG2oeROSd sBkLpRC7HZBPaDFw4wP2IPgVJfI8iQlDlAcHAObpRpN/iKv6Gf/NQOWsoXAl6kesv2oDIRPs5v/ pT8Hipf+z0z78D2GmPA== X-Google-Smtp-Source: AGHT+IEjUBMQGoVxUfyDuWsIaZh++ce8Z93gQtTGPdxEJaJNt3LFU5j/zdaAt8Gsv0XYS4ZhQjjGAb/v4s3GhzQ= X-Received: from wmgg22.prod.google.com ([2002:a05:600d:16:b0:46f:c7ab:c8ce]) (user=aliceryhl job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:295:b0:46f:b42e:e362 with SMTP id 5b1f17b1804b1-475d244d6f1mr13867525e9.19.1761302351572; Fri, 24 Oct 2025 03:39:11 -0700 (PDT) Date: Fri, 24 Oct 2025 10:39:10 +0000 In-Reply-To: <20251022143158.64475-3-dakr@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20251022143158.64475-1-dakr@kernel.org> <20251022143158.64475-3-dakr@kernel.org> Message-ID: Subject: Re: [PATCH v3 02/10] rust: uaccess: add UserSliceReader::read_slice_partial() From: Alice Ryhl To: Danilo Krummrich Cc: gregkh@linuxfoundation.org, rafael@kernel.org, ojeda@kernel.org, alex.gaynor@gmail.com, boqun.feng@gmail.com, gary@garyguo.net, bjorn3_gh@protonmail.com, lossin@kernel.org, a.hindborg@kernel.org, tmgross@umich.edu, mmaurer@google.com, rust-for-linux@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" On Wed, Oct 22, 2025 at 04:30:36PM +0200, Danilo Krummrich wrote: > The existing read_slice() method is a wrapper around copy_from_user() > and expects the user buffer to be larger than the destination buffer. > > However, userspace may split up writes in multiple partial operations > providing an offset into the destination buffer and a smaller user > buffer. > > In order to support this common case, provide a helper for partial > reads. > > Reviewed-by: Greg Kroah-Hartman > Reviewed-by: Matthew Maurer > Signed-off-by: Danilo Krummrich > --- > rust/kernel/uaccess.rs | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs > index a8fb4764185a..c1cd3a76cff8 100644 > --- a/rust/kernel/uaccess.rs > +++ b/rust/kernel/uaccess.rs > @@ -287,6 +287,22 @@ pub fn read_slice(&mut self, out: &mut [u8]) -> Result { > self.read_raw(out) > } > > + /// Reads raw data from the user slice into a kernel buffer partially. > + /// > + /// This is the same as [`Self::read_slice`] but considers the given `offset` into `out` and > + /// truncates the read to the boundaries of `self` and `out`. > + /// > + /// On success, returns the number of bytes read. > + pub fn read_slice_partial(&mut self, out: &mut [u8], offset: usize) -> Result { > + let end = offset > + .checked_add(self.len()) > + .unwrap_or(out.len()) > + .min(out.len()); > + > + out.get_mut(offset..end) > + .map_or(Ok(0), |dst| self.read_slice(dst).map(|()| dst.len())) Same comment applies as write_slice_partial(). Reviewed-by: Alice Ryhl