* Rename FdEntry to Entry
* Add custom FdSet container for managing fd allocs/deallocs
This commit adds a custom `FdSet` container which is intended
for use in `wasi-common` to track WASI fd allocs/deallocs. The
main aim for this container is to abstract away the current
approach of spawning new handles
```rust
fd = fd.checked_add(1).ok_or(...)?;
```
and to make it possible to reuse unused/reclaimed handles
which currently is not done.
The struct offers 3 methods to manage its functionality:
* `FdSet::new` initialises the internal data structures,
and most notably, it preallocates an `FdSet::BATCH_SIZE`
worth of handles in such a way that we always start popping
from the "smallest" handle (think of it as of reversed stack,
I guess; it's not a binary heap since we don't really care
whether internally the handles are sorted in some way, just that
the "largets" handle is at the bottom. Why will become clear
when describing `allocate` method.)
* `FdSet::allocate` pops the next available handle if one is available.
The tricky bit here is that, if we run out of handles, we preallocate
the next `FdSet::BATCH_SIZE` worth of handles starting from the
latest popped handle (i.e., the "largest" handle). This
works only because we make sure to only ever pop and push already
existing handles from the back, and push _new_ handles (from the
preallocation step) from the front. When we ultimately run out
of _all_ available handles, we then return `None` for the client
to handle in some way (e.g., throwing an error such as `WasiError::EMFILE`
or whatnot).
* `FdSet::deallocate` returns the already allocated handle back to
the pool for further reuse.
When figuring out the internals, I've tried to optimise for both
alloc and dealloc performance, and I believe we've got an amortised
`O(1)~*` performance for both (if my maths is right, and it may very
well not be, so please verify!).
In order to keep `FdSet` fairly generic, I've made sure not to hard-code
it for the current type system generated by `wig` (i.e., `wasi::__wasi_fd_t`
representing WASI handle), but rather, any type which wants to be managed
by `FdSet` needs to conform to `Fd` trait. This trait is quite simple as
it only requires a couple of rudimentary traits (although `std:#️⃣:Hash`
is quite a powerful assumption here!), and a custom method
```rust
Fd::next(&self) -> Option<Self>;
```
which is there to encapsulate creating another handle from the given one.
In the current state of the code, that'd be simply `u32::checked_add(1)`.
When `wiggle` makes it way into the `wasi-common`, I'd imagine it being
similar to
```rust
fn next(&self) -> Option<Self> {
self.0.checked_add(1).map(Self::from)
}
```
Anyhow, I'd be happy to learn your thoughts about this design!
* Fix compilation on other targets
* Rename FdSet to FdPool
* Fix FdPool unit tests
* Skip preallocation step in FdPool
* Replace 'replace' calls with direct assignment
* Reuse FdPool from snapshot1 in snapshot0
* Refactor FdPool::allocate
* Remove entry before deallocating the fd
* Refactor the design to accommodate `u32` as underlying type
This commit refactors the design by ensuring that the underlying
type in `FdPool` which we use to track and represent raw file
descriptors is `u32`. As a result, the structure of `FdPool` is
simplified massively as we no longer need to track the claimed
descriptors; in a way, we trust the caller to return the handle
after it's done with it. In case the caller decides to be clever
and return a handle which was not yet legally allocated, we panic.
This should never be a problem in `wasi-common` unless we hit a
bug.
To make all of this work, `Fd` trait is modified to require two
methods: `as_raw(&self) -> u32` and `from_raw(raw_fd: u32) -> Self`
both of which are used to convert to and from the `FdPool`'s underlying
type `u32`.
* Introduce WasiCtxBuilderError error type
`WasiCtxBuilderError` is the `wasi-common` client-facing error type
which is exclusively thrown when building a new `WasiCtx` instance.
As such, building such an instance should not require the client to
understand different WASI errno values as was assumed until now.
This commit is a first step at streamlining error handling in
`wasi-common` and makes way for the `wiggle` crate.
When adding the `WasiCtxBuilderError`, I've had to do two things of
notable importance:
1. I've removed a couple of `ok_or` calls in `WasiCtxBuilder::build`
and replaced them with `unwrap`s, following the same pattern in
different builder methods above. This is fine since we _always_
operate on non-empty `Option`s in `WasiCtxBuilder` thus `unwrap`ing
will never fail. On the other hand, this might be a good opportunity
to rethink the structure of our builder, and how we good remove
the said `Option`s especially since we always populate them with
empty containers to begin with. I understand this is to make
chaining of builder methods easier which take and return `&mut self`
and the same applies to `WasiCtxBuilder::build(&mut self)` method,
but perhaps it would more cleanly signal the intentions if we simply
moved `WasiCtxBuilder` instance around. Food for thought!
2. Methods specific to determining rights of passed around `std::fs::File`
objects when populating `WasiCtx` `FdEntry` entities now return
`io::Error` directly so that we can reuse them in `WasiCtxBuilder` methods
(returning `WasiCtxBuilderError` error type), and in syscalls
(returning WASI errno).
* Return WasiError directly in syscalls
Also, removes `error::Error` type altogether. Now, `io::Error` and
related are automatically converted to their corresponding WASI
errno value encapsulated as `WasiError`.
While here, it made sense to me to move `WasiError` to `wasi` module
which will align itself well with the upcoming changes introduced
by `wiggle`. To different standard `Result` from WASI specific, I've
created a helper alias `WasiResult` also residing in `wasi` module.
* Update wig
* Add from ffi::NulError and pass context to NotADirectory
* Add dummy commit to test CI
* Winx now returns io::Error
This commit is a spiritual follower of #1242 in the sense that it
adjusts `winx` to also return `io::Error` directly rather than
tossing a custom error type here and there.
* Adapt wasi-common to changes in winx
* Run cargo fmt
* Swap overly big map_err with explicit match
* Add support for virtual files (eg, not backed by an OS file).
Virtual files are implemented through trait objects, with a default
implementation that tries to behave like on-disk files, but entirely
backed by in-memory structures.
Co-authored-by: Dan Gohman <sunfish@mozilla.com>
* Add support for wasi_snapshot_preview1.
This adds support for the new ABI, while preserving compatibility
support for the old ABI.
* Fix compilation on platforms where nlink_t isn't 64-bit.
* rustfmt
* Fix Windows build errors.
