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This avoids requiring callers of versioned UAPIs to convert values to byte slices and truncate them manually. Signed-off-by: Alistair Popple Suggested-by: Danilo Krummrich --- rust/kernel/uaccess.rs | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs index 5f6c4d7a1a51..c63b91942631 100644 --- a/rust/kernel/uaccess.rs +++ b/rust/kernel/uaccess.rs @@ -624,6 +624,20 @@ pub fn write(&mut self, value: &T) -> Result { self.length -= len; Ok(()) } + + /// Writes as much of the provided value as fits in the remaining buffer. + /// + /// Copies `min(size_of::(), self.len())` bytes to userspace. Returns the number of bytes + /// actually written. This is useful for versioned structs where an older userspace may provide + /// a smaller buffer than the current kernel struct. + /// + /// Fails with [`EFAULT`] if the write happens on a bad address. This call may modify the + /// associated userspace slice even if it returns an error. + pub fn write_truncated(&mut self, value: &T) -> Result { + let len = self.length.min(size_of::()); + self.write_slice(&value.as_bytes()[..len])?; + Ok(len) + } } /// Reads a nul-terminated string into `dst` and returns the length. -- 2.54.0