Re: [PATCH v11 6/8] mm: rust: add VmAreaNew for f_ops->mmap()

[Andreas Hindborg <a.hindborg@kernel.org>]

"Alice Ryhl" <aliceryhl@google.com> writes:

> This type will be used when setting up a new vma in an f_ops->mmap()
> hook. Using a separate type from VmAreaRef allows us to have a separate
> set of operations that you are only able to use during the mmap() hook.
> For example, the VM_MIXEDMAP flag must not be changed after the initial
> setup that happens during the f_ops->mmap() hook.
>
> To avoid setting invalid flag values, the methods for clearing
> VM_MAYWRITE and similar involve a check of VM_WRITE, and return an error
> if VM_WRITE is set. Trying to use `try_clear_maywrite` without checking
> the return value results in a compilation error because the `Result`
> type is marked #[must_use].
>
> For now, there's only a method for VM_MIXEDMAP and not VM_PFNMAP. When
> we add a VM_PFNMAP method, we will need some way to prevent you from
> setting both VM_MIXEDMAP and VM_PFNMAP on the same vma.
>
> Acked-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> (for mm bits)
> Reviewed-by: Jann Horn <jannh@google.com>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> ---
>  rust/kernel/mm/virt.rs | 181 ++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 180 insertions(+), 1 deletion(-)
>
> diff --git a/rust/kernel/mm/virt.rs b/rust/kernel/mm/virt.rs
> index 3a23854e14f4..6d9ba56d4f95 100644
> --- a/rust/kernel/mm/virt.rs
> +++ b/rust/kernel/mm/virt.rs
> @@ -6,7 +6,7 @@
>
>  use crate::{
>      bindings,
> -    error::{to_result, Result},
> +    error::{code::EINVAL, to_result, Result},
>      mm::MmWithUser,
>      page::Page,
>      types::Opaque,
> @@ -171,6 +171,185 @@ pub fn vm_insert_page(&self, address: usize, page: &Page) -> Result {
>      }
>  }
>
> +/// A builder for setting up a vma in an `f_ops->mmap()` hook.

Reading this line, I would expect to be able to chain update methods as
in `Builder::new().prop_a().prop_b().build()`. Could/should this type
accommodate a proper builder pattern? Or is "builder" not the right word
to use here?


Best regards,
Andreas Hindborg