Re: File operations

[Wedson Almeida Filho <wedsonaf@google.com>]

On Sun, 13 Dec 2020 at 03:33, Miguel Ojeda
<miguel.ojeda.sandonis@gmail.com> wrote:

> For instance, could the user define a type with only the methods they
> need and then construct the `file_operations` struct (perhaps
> abstracted the builder pattern)? The codegen/performance should be OK,
> since all the values would be known. The downside is that you need to
> actually repeat your functions in the builder, but the positive side
> is that the code is way more straightforward, no macros, etc.

Hmm, I hadn't thought of using the builder pattern. I need to think
about it some more.

But one potential issue that comes immediately to mind is that with a
builder pattern, the value is created at run time. In our case, this
is undesirable because this table contains function pointers: if we
leave them in writable memory, they will become easy targets when
attackers have write-vulnerabilities that they want to elevate to
arbitrary execution; leaving the vtable in rdata (i.e., in read-only
pages) is much preferable. This means that we need const functions,
but we cannot have them in traits.

If we are ok with repeating function names, I have a solution with a
much simpler macro. Of course, it is simple enough that clients can
just ignore it and define the const themselves if they want to avoid
macros at all costs. What do you think of
https://github.com/Rust-for-Linux/linux/commit/13b2f2c47e62ad5bf824f7e15e14090c90a4ba9e
?

Cheers,
-Wedson