From f2af7b01b05545fff1cea0768c14e2da552a56ee Mon Sep 17 00:00:00 2001 From: Danilo Krummrich Date: Wed, 22 Oct 2025 16:30:36 +0200 Subject: [PATCH] rust: uaccess: add UserSliceReader::read_slice_partial() 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 Reviewed-by: Alice Ryhl Reviewed-by: Alexandre Courbot Acked-by: Miguel Ojeda [ Replace map_or() with let-else; use saturating_add(). - Danilo ] Signed-off-by: Danilo Krummrich --- rust/kernel/uaccess.rs | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs index a8fb4764185a1..1409cb9070157 100644 --- a/rust/kernel/uaccess.rs +++ b/rust/kernel/uaccess.rs @@ -287,6 +287,23 @@ impl UserSliceReader { 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.saturating_add(self.len()).min(out.len()); + + let Some(dst) = out.get_mut(offset..end) else { + return Ok(0); + }; + + self.read_slice(dst)?; + Ok(dst.len()) + } + /// Reads a value of the specified type. /// /// Fails with [`EFAULT`] if the read happens on a bad address, or if the read goes out of -- 2.47.3