On 11/30/23 16:58, Theodore Ts'o wrote: > On Thu, Nov 30, 2023 at 03:46:55PM +0000, Benno Lossin wrote: >>>>> + pub const O_APPEND: u32 = bindings::O_APPEND; >>>> >>>> Why do all of these constants begin with `O_`? >>> >>> Because that is how they are defined in the kernel in the C code. Why >>> would they not be the same here? >> >> Then why does the C side name them that way? Is it because `O_*` is >> supposed to mean something, or is it done due to namespacing? > > It's because these sets of constants were flags passed to the open(2) > system call, and so they are dictated by the POSIX specification. So > O_ means that they are a set of integer values which are used by > open(2), and they are defined when userspace #include's the fcntl.h > header file. One could consider it be namespacing --- we need to > distinguish these from other constants: MAY_APPEND, RWF_APPEND, > ESCAPE_APPEND, STATX_ATTR_APPEND, BTRFS_INODE_APPEND. > > But it's also a convention that dates back for ***decades*** and if we > want code to be understandable by kernel programmers, we need to obey > standard kernel naming conventions. I see, that makes a lot of sense. Thanks for the explanation. >> In Rust we have namespacing, so we generally drop common prefixes. > > I don't know about Rust namespacing, but in other languages, how you > have to especify namespaces tend to be ***far*** more verbose than > just adding an O_ prefix. In this case we already have the `flags` namespace, so I thought about just dropping the `O_` prefix altogether. -- Cheers, Benno
