Take all AsFds by ref?

[SUPERCILEX]

Every function current passes in AsFd by value. This is safe, but a little weird because you can do read(owned_fd, ...) and close the fd within the read call. Was this considered? Or a design mistake?

[sunfishcode]

Earlier versions of rustix did pass the AsFd by reference, and it was changed to pass it by value.

• This makes it work more like AsRef<Path>, which is typically passed by value rather than by reference.
• Users were writing code passing AsFd by value even when rustix and io-lifetimes and all the docs demonstrated it by passing it by reference, which suggested that passing by value was the more intuitive way.
• Passing by value means users need fewer &s.

The fact that it can cause an owning type to be dropped was considered. It is a little surprising, but if you intend to use the owned type for anything afterwards, you'll get a compiler error, rather than a runtime surprise, so it seemed an ok tradeoff.

[SUPERCILEX]

Sounds like a reasonable conclusion, thanks for the details. nix-rust/nix#1863 should probably follow suite then. Thanks again!