* Compile wasi-common to Emscripten
This commit enables cross-compiling of `wasi-common` to Emscripten. To achieve
this, this commit does quite a bit reshuffling in the existing codebase. Namely,
* rename `linux` modules in `wasi-common` and `yanix` to `linux_like` -- this is
needed so that we can separate out logic specific to Linux and Emscripten out
* tweak `dir` module in `yanix` to support Emscripten -- in particular, the main
change involves `SeekLoc::from_raw` which has to be now host-specific, and is now
fallible
* tweak `filetime` so that in Emscripten we never check for existence of `utimensat`
at runtime since we are guaranteed for it to exist by design
* since `utimes` and `futimes` are not present in Emscripten, move them into a separate
module, `utimesat`, and tag it cfg-non-emscripten only
* finally, `to_timespec` is now fallible since on Emscripten we have to cast number of
seconds, `FileTime::seconds` from `i64` to `libc::c_long` which resolves to `i32`
unlike on other nixes
* Fix macos build
* Verify wasi-common compiles to Emscripten
This commit adds `emscripten` job to Github Actions which installs
`wasm32-unknown-emscripten` target, and builds `wasi-common` crate.
* Use #[path] to cherry-pick mods for Emscripten
This commit effectively reverses the reorg introduced in 145f4a5
in that it ditches `linux_like` mod for separate mods `linux` and
`emscripten` which are now on the same crate level, and instead,
pulls in common bits from `linux` using the `#[path = ..]` proc
macro.
* Dynamically load utimensat if exists on the host
This commit introduces a change to file time management for *nix based
hosts in that it firstly tries to load `utimensat` symbol, and if it
doesn't exist, then falls back to `utimes` instead. This change is
borrowing very heavily from [filetime] crate, however, it introduces a
couple of helpers and methods specific to WASI use case (or more
generally, to a use case which requires modifying times of entities
specified by a pair `(DirFD, RelativePath)` rather than the typical
file time specification based only absolute path or raw file descriptor
as is the case with [filetime] crate. The trick here is, that on kernels
which do not have `utimensat` symbol, this implementation emulates this
behaviour by a combination of `openat` and `utimes`.
This commit also is meant to address #516.
[filetime]: https://github.com/alexcrichton/filetime
* Fix symlink NOFOLLOW flag setting
* Add docs and specify UTIME_NOW/OMIT on Linux
Previously, we relied on [libc] crate for `UTIME_NOW` and `UTIME_OMIT`
constants on Linux. However, following the convention assumed in
[filetime] crate, this is now changed to directly specified by us
in our crate.
[libc]: https://github.com/rust-lang/libc
[filetime]: https://github.com/alexcrichton/filetime
* Refactor UTIME_NOW/OMIT for BSD
* Address final discussion points
