Messages in this thread | | | Date | Tue, 8 Aug 2023 23:59:04 -0300 | From | Martin Rodriguez Reboredo <> | Subject | Re: [RFC PATCH v1 1/5] rust: file: add bindings for `struct file` |
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On 7/20/23 12:28, Alice Ryhl wrote: > From: Wedson Almeida Filho <walmeida@microsoft.com> > > Using these bindings it becomes possible to access files from drivers > written in Rust. This patch only adds support for accessing the flags, > and for managing the refcount of the file. > > Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com> > Co-Developed-by: Daniel Xu <dxu@dxuuu.xyz> > Signed-off-by: Daniel Xu <dxu@dxuuu.xyz> > Co-Developed-by: Alice Ryhl <aliceryhl@google.com> > Signed-off-by: Alice Ryhl <aliceryhl@google.com> > --- > In this patch, I am defining an error type called `BadFdError`. I'd like > your thoughts on doing it this way vs just using the normal `Error` > type. > > Pros: > * The type system makes it clear that the function can only fail with > EBADF, and that no other errors are possible. > * Since the compiler knows that `ARef<Self>` cannot be null and that > `BadFdError` has only one possible value, the return type of > `File::from_fd` is represented as a pointer with null being an error. > > Cons: > * Defining additional error types involves boilerplate. > * The return type becomes a tagged union, making it larger than a > pointer.
These two are kinda passable, as a `impl_null_ptr_err` macro can be opted to implement error types from nulls. Also if we consider that `File::from_fd` isn't going to be called a gorillion times a second or a recursive call is done, then I'd say that the tagged union won't bring any other problems, except that a compiler optim is skipped.
> * The question mark operator will only utilize the `From` trait once, > which prevents you from using the question mark operator on > `BadFdError` in methods that return some third error type that the > kernel `Error` is convertible into.
Although, I want this to be mentioned in the doc of `BadFdError` as this cannot be overlooked when said usage of `?` is done.
> > rust/bindings/bindings_helper.h | 2 + > rust/helpers.c | 7 ++ > rust/kernel/file.rs | 176 ++++++++++++++++++++++++++++++++ > rust/kernel/lib.rs | 1 + > 4 files changed, 186 insertions(+) > create mode 100644 rust/kernel/file.rs > > [...] > diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h > [...] > diff --git a/rust/helpers.c b/rust/helpers.c > [...]
This one is making my head spin, shouldn't they go first?
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