Add UserSliceReader::read_slice_file(), which is the same as
UserSliceReader::read_slice_partial() but updates the given file::Offset
by the number of bytes read.

This is equivalent to C's `simple_write_to_buffer()` and useful when
dealing with file offsets from file operations.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/uaccess.rs | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs
index c1cd3a76cff8..c2d3dfee8934 100644
--- a/rust/kernel/uaccess.rs
+++ b/rust/kernel/uaccess.rs
@@ -9,6 +9,7 @@
     bindings,
     error::Result,
     ffi::{c_char, c_void},
+    fs::file,
     prelude::*,
     transmute::{AsBytes, FromBytes},
 };
@@ -303,6 +304,30 @@ pub fn read_slice_partial(&mut self, out: &mut [u8], offset: usize) -> Result<us
             .map_or(Ok(0), |dst| self.read_slice(dst).map(|()| dst.len()))
     }
 
+    /// Reads raw data from the user slice into a kernel buffer partially.
+    ///
+    /// This is the same as [`Self::read_slice_partial`] but updates the given [`file::Offset`] by
+    /// the number of bytes read.
+    ///
+    /// This is equivalent to C's `simple_write_to_buffer()`.
+    ///
+    /// On success, returns the number of bytes read.
+    pub fn read_slice_file(&mut self, out: &mut [u8], offset: &mut file::Offset) -> Result<usize> {
+        if offset.is_negative() {
+            return Err(EINVAL);
+        }
+
+        let Ok(offset_index) = (*offset).try_into() else {
+            return Ok(0);
+        };
+
+        let read = self.read_slice_partial(out, offset_index)?;
+
+        *offset = offset.saturating_add_usize(read);
+
+        Ok(read)
+    }
+
     /// 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
-- 
2.51.0

On Wed Oct 22, 2025 at 11:30 PM JST, Danilo Krummrich wrote:
> Add UserSliceReader::read_slice_file(), which is the same as
> UserSliceReader::read_slice_partial() but updates the given file::Offset
> by the number of bytes read.
>
> This is equivalent to C's `simple_write_to_buffer()` and useful when
> dealing with file offsets from file operations.
>
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> ---
>  rust/kernel/uaccess.rs | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
>
> diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs
> index c1cd3a76cff8..c2d3dfee8934 100644
> --- a/rust/kernel/uaccess.rs
> +++ b/rust/kernel/uaccess.rs
> @@ -9,6 +9,7 @@
>      bindings,
>      error::Result,
>      ffi::{c_char, c_void},
> +    fs::file,
>      prelude::*,
>      transmute::{AsBytes, FromBytes},
>  };
> @@ -303,6 +304,30 @@ pub fn read_slice_partial(&mut self, out: &mut [u8], offset: usize) -> Result<us
>              .map_or(Ok(0), |dst| self.read_slice(dst).map(|()| dst.len()))
>      }
>  
> +    /// Reads raw data from the user slice into a kernel buffer partially.
> +    ///
> +    /// This is the same as [`Self::read_slice_partial`] but updates the given [`file::Offset`] by
> +    /// the number of bytes read.
> +    ///
> +    /// This is equivalent to C's `simple_write_to_buffer()`.
> +    ///
> +    /// On success, returns the number of bytes read.
> +    pub fn read_slice_file(&mut self, out: &mut [u8], offset: &mut file::Offset) -> Result<usize> {
> +        if offset.is_negative() {
> +            return Err(EINVAL);
> +        }
> +
> +        let Ok(offset_index) = (*offset).try_into() else {
> +            return Ok(0);
> +        };
> +
> +        let read = self.read_slice_partial(out, offset_index)?;
> +
> +        *offset = offset.saturating_add_usize(read);
> +
> +        Ok(read)

Not sure whether this would be better, but you can avoid the `read`
local variable with the following:

    self.read_slice_partial(out, offset_index)
        .inspect(|&read| *offset = offset.saturating_add_usize(read))

In any case,

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>