On Fri, Apr 16, 2021 at 07:47:32PM +0200, Miguel Ojeda wrote:
> On Fri, Apr 16, 2021 at 7:05 PM Linus Torvalds
> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > Typical Rust error handling should match the regular kernel
> > IS_ERR/ERR_PTR/PTR_ERR model fairly well, although the syntax is
> > fairly different (and it's not limited to pointers).
>
> Yeah, exactly. We already have a `KernelResult<T>` type which is a
> `Result<T, Error>`, where `Error` is a wrapper for the usual kernel
> int errors.
>
> So, for instance, a function that can either fail or return `Data`
> would have a declaration like:
>
> pub fn foo() -> KernelResult<Data>
>
> A caller that needs to handle the error can use pattern matching or
> one of the methods in `Result`. And if they only need to bubble the
> error up, they can use the ? operator:
>
> pub fn bar() -> KernelResult<Data> {
> let data = foo()?;
>
> // `data` is already a `Data` here, not a `KernelResult<Data>`
> }
Umm... A fairly common situation is
foo() returns a pointer to struct foo instance or ERR_PTR()
bar() returns a pointer to struct bar instance of ERR_PTR()
bar()
{
struct foo *p;
struct bar *res;
.... // do some work, grab a mutex, etc.
p = foo();
if (IS_ERR(p))
res = ERR_CAST(p); // (void *)p, internally; conceptually it's
// ERR_PTR(PTR_ERR(p));
else
res = blah();
.... // matching cleanup
return res;
}
How well would ? operator fit that pattern? _If_ it's just a syntax sugar
along the lines of "if argument matches Err(_), return Err(_)", the types
shouldn't be an issue, but that might need some fun with releasing resources,
etc. If it's something more elaborate... details, please.
