Re: [PATCH] rust: generalize userSliceReader to support any Vec

[Boqun Feng <boqun.feng@gmail.com>]

On Sun, Dec 22, 2024 at 01:37:02PM -0300, Filipe Xavier wrote:
> The UserSliceReader::read_all function is currently restricted to use
> only Vec with the kmalloc allocator.
> However, there is no reason for this limitation.
> This patch generalizes the function to accept any Vec regardless of the
> allocator used.
> 

Interesting idea, however...

> Link: https://github.com/Rust-for-Linux/linux/issues/1136
> Signed-off-by: Filipe Xavier <felipeaggger@gmail.com>
> ---
>  rust/kernel/uaccess.rs | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/rust/kernel/uaccess.rs b/rust/kernel/uaccess.rs
> index cc044924867b89f6116c7f9ec216d8cea2b3f8d7..719b0a48ff5550acc19f2e607c0a09f818145def 100644
> --- a/rust/kernel/uaccess.rs
> +++ b/rust/kernel/uaccess.rs
> @@ -5,7 +5,7 @@
>  //! C header: [`include/linux/uaccess.h`](srctree/include/linux/uaccess.h)
>  
>  use crate::{
> -    alloc::Flags,
> +    alloc::{Allocator, Flags},
>      bindings,
>      error::Result,
>      ffi::c_void,
> @@ -127,7 +127,7 @@ pub fn new(ptr: UserPtr, length: usize) -> Self {
>      /// Reads the entirety of the user slice, appending it to the end of the provided buffer.
>      ///
>      /// Fails with [`EFAULT`] if the read happens on a bad address.
> -    pub fn read_all(self, buf: &mut KVec<u8>, flags: Flags) -> Result {
> +    pub fn read_all<A: Allocator>(self, buf: &mut Vec<u8, A>, flags: Flags) -> Result {
>          self.reader().read_all(buf, flags)
>      }
>  
> @@ -281,7 +281,7 @@ pub fn read<T: FromBytes>(&mut self) -> Result<T> {
>      /// Reads the entirety of the user slice, appending it to the end of the provided buffer.
>      ///
>      /// Fails with [`EFAULT`] if the read happens on a bad address.
> -    pub fn read_all(mut self, buf: &mut KVec<u8>, flags: Flags) -> Result {
> +    pub fn read_all<A: Allocator>(mut self, buf: &mut Vec<u8, A>, flags: Flags) -> Result {

... what if the copy hit a page fault because the target memory (e.g. a
VVec) is not mapped? Would copy_from_user() handle this? Or would it
return a different error code than `EFAULT`?

Do you have a usage of usig this functionality?

Regards,
Boqun

>          let len = self.length;
>          buf.reserve(len, flags)?;
>  
> 
> ---
> base-commit: 0c5928deada15a8d075516e6e0d9ee19011bb000
> change-id: 20241222-gen-userslice-readall-alloc-8049c668e65e
> 
> Best regards,
> -- 
> Filipe Xavier <felipeaggger@gmail.com>
>