On 11/29/23 13:51, Alice Ryhl wrote:
> +/// Flags associated with a [`File`].
> +pub mod flags {
> + /// File is opened in append mode.
> + pub const O_APPEND: u32 = bindings::O_APPEND;
Why do all of these constants begin with `O_`?
[...]
> +impl File {
> + /// Constructs a new `struct file` wrapper from a file descriptor.
> + ///
> + /// The file descriptor belongs to the current process.
> + pub fn from_fd(fd: u32) -> Result<ARef<Self>, BadFdError> {
> + // SAFETY: FFI call, there are no requirements on `fd`.
> + let ptr = ptr::NonNull::new(unsafe { bindings::fget(fd) }).ok_or(BadFdError)?;
> +
> + // INVARIANT: `fget` increments the refcount before returning.
> + Ok(unsafe { ARef::from_raw(ptr.cast()) })
Missing `SAFETY` comment.
> + }
> +
> + /// Creates a reference to a [`File`] from a valid pointer.
> + ///
> + /// # Safety
> + ///
> + /// The caller must ensure that `ptr` points at a valid file and that its refcount does not
> + /// reach zero during the lifetime 'a.
> + pub unsafe fn from_ptr<'a>(ptr: *const bindings::file) -> &'a File {
> + // INVARIANT: The safety requirements guarantee that the refcount does not hit zero during
> + // 'a. The cast is okay because `File` is `repr(transparent)`.
> + unsafe { &*ptr.cast() }
Missing `SAFETY` comment.
> + }
> +
> + /// Returns the flags associated with the file.
> + ///
> + /// The flags are a combination of the constants in [`flags`].
> + pub fn flags(&self) -> u32 {
> + // This `read_volatile` is intended to correspond to a READ_ONCE call.
> + //
> + // SAFETY: The file is valid because the shared reference guarantees a nonzero refcount.
> + //
> + // TODO: Replace with `read_once` when available on the Rust side.
> + unsafe { core::ptr::addr_of!((*self.0.get()).f_flags).read_volatile() }
> + }
> +}
> +
> +// SAFETY: The type invariants guarantee that `File` is always ref-counted.
> +unsafe impl AlwaysRefCounted for File {
> + fn inc_ref(&self) {
> + // SAFETY: The existence of a shared reference means that the refcount is nonzero.
> + unsafe { bindings::get_file(self.0.get()) };
> + }
> +
> + unsafe fn dec_ref(obj: ptr::NonNull<Self>) {
> + // SAFETY: The safety requirements guarantee that the refcount is nonzero.
> + unsafe { bindings::fput(obj.cast().as_ptr()) }
> + }
> +}
> +
> +/// Represents the `EBADF` error code.
> +///
> +/// Used for methods that can only fail with `EBADF`.
> +pub struct BadFdError;
> +
> +impl From<BadFdError> for Error {
> + fn from(_: BadFdError) -> Error {
> + EBADF
> + }
> +}
> +
> +impl core::fmt::Debug for BadFdError {
> + fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
> + f.pad("EBADF")
> + }
> +}
Do we want to generalize this to the other errors as well? We could modify
the `declare_error!` macro in `error.rs` to create these unit structs.
--
Cheers,
Benno
