diff options
Diffstat (limited to 'rust/kernel/iov.rs')
| -rw-r--r-- | rust/kernel/iov.rs | 143 |
1 files changed, 143 insertions, 0 deletions
diff --git a/rust/kernel/iov.rs b/rust/kernel/iov.rs index 01f4b90ff8b4..43bae8923c46 100644 --- a/rust/kernel/iov.rs +++ b/rust/kernel/iov.rs @@ -16,6 +16,15 @@ use crate::{ use core::{marker::PhantomData, mem::MaybeUninit, ptr, slice}; const ITER_SOURCE: bool = bindings::ITER_SOURCE != 0; +const ITER_DEST: bool = bindings::ITER_DEST != 0; + +// Compile-time assertion for the above constants. +const _: () = { + build_assert!( + ITER_SOURCE != ITER_DEST, + "ITER_DEST and ITER_SOURCE should be different." + ); +}; /// An IO vector that acts as a source of data. /// @@ -169,3 +178,137 @@ impl<'data> IovIterSource<'data> { unsafe { slice::from_raw_parts_mut(out, len) } } } + +/// An IO vector that acts as a destination for data. +/// +/// IO vectors support many different types of destinations. This includes both buffers in +/// kernel-space and writing to userspace. It's possible that the destination buffer is mapped in a +/// thread-local manner using e.g. `kmap_local_page()`, so this type is not `Send` to ensure that +/// the mapping is written to the right context in that scenario. +/// +/// # Invariants +/// +/// Must hold a valid `struct iov_iter` with `data_source` set to `ITER_DEST`. For the duration of +/// `'data`, it must be safe to write to this IO vector using the standard C methods for this +/// purpose. +#[repr(transparent)] +pub struct IovIterDest<'data> { + iov: Opaque<bindings::iov_iter>, + /// Represent to the type system that this value contains a pointer to writable data it does + /// not own. + _source: PhantomData<&'data mut [u8]>, +} + +impl<'data> IovIterDest<'data> { + /// Obtain an `IovIterDest` from a raw pointer. + /// + /// # Safety + /// + /// * The referenced `struct iov_iter` must be valid and must only be accessed through the + /// returned reference for the duration of `'iov`. + /// * The referenced `struct iov_iter` must have `data_source` set to `ITER_DEST`. + /// * For the duration of `'data`, it must be safe to write to this IO vector using the + /// standard C methods for this purpose. + #[track_caller] + #[inline] + pub unsafe fn from_raw<'iov>(ptr: *mut bindings::iov_iter) -> &'iov mut IovIterDest<'data> { + // SAFETY: The caller ensures that `ptr` is valid. + let data_source = unsafe { (*ptr).data_source }; + assert_eq!(data_source, ITER_DEST); + + // SAFETY: The caller ensures the type invariants for the right durations, and + // `IovIterSource` is layout compatible with `struct iov_iter`. + unsafe { &mut *ptr.cast::<IovIterDest<'data>>() } + } + + /// Access this as a raw `struct iov_iter`. + #[inline] + pub fn as_raw(&mut self) -> *mut bindings::iov_iter { + self.iov.get() + } + + /// Returns the number of bytes available in this IO vector. + /// + /// Note that this may overestimate the number of bytes. For example, reading from userspace + /// memory could fail with EFAULT, which will be treated as the end of the IO vector. + #[inline] + pub fn len(&self) -> usize { + // SAFETY: We have shared access to this IO vector, so we can read its `count` field. + unsafe { + (*self.iov.get()) + .__bindgen_anon_1 + .__bindgen_anon_1 + .as_ref() + .count + } + } + + /// Returns whether there are any bytes left in this IO vector. + /// + /// This may return `true` even if there are no more bytes available. For example, reading from + /// userspace memory could fail with EFAULT, which will be treated as the end of the IO vector. + #[inline] + pub fn is_empty(&self) -> bool { + self.len() == 0 + } + + /// Advance this IO vector by `bytes` bytes. + /// + /// If `bytes` is larger than the size of this IO vector, it is advanced to the end. + #[inline] + pub fn advance(&mut self, bytes: usize) { + // SAFETY: By the type invariants, `self.iov` is a valid IO vector. + unsafe { bindings::iov_iter_advance(self.as_raw(), bytes) }; + } + + /// Advance this IO vector backwards by `bytes` bytes. + /// + /// # Safety + /// + /// The IO vector must not be reverted to before its beginning. + #[inline] + pub unsafe fn revert(&mut self, bytes: usize) { + // SAFETY: By the type invariants, `self.iov` is a valid IO vector, and the caller + // ensures that `bytes` is in bounds. + unsafe { bindings::iov_iter_revert(self.as_raw(), bytes) }; + } + + /// Write data to this IO vector. + /// + /// Returns the number of bytes that were written. If this is shorter than the provided slice, + /// then no more bytes can be written. + #[inline] + pub fn copy_to_iter(&mut self, input: &[u8]) -> usize { + // SAFETY: + // * By the type invariants, it is still valid to write to this IO vector. + // * `input` is valid for `input.len()` bytes. + unsafe { bindings::_copy_to_iter(input.as_ptr().cast(), input.len(), self.as_raw()) } + } + + /// Utility for implementing `read_iter` given the full contents of the file. + /// + /// The full contents of the file being read from is represented by `contents`. This call will + /// write the appropriate sub-slice of `contents` and update the file position in `ppos` so + /// that the file will appear to contain `contents` even if takes multiple reads to read the + /// entire file. + #[inline] + pub fn simple_read_from_buffer(&mut self, ppos: &mut i64, contents: &[u8]) -> Result<usize> { + if *ppos < 0 { + return Err(EINVAL); + } + let Ok(pos) = usize::try_from(*ppos) else { + return Ok(0); + }; + if pos >= contents.len() { + return Ok(0); + } + + // BOUNDS: We just checked that `pos < contents.len()` above. + let num_written = self.copy_to_iter(&contents[pos..]); + + // OVERFLOW: `pos+num_written <= contents.len() <= isize::MAX <= i64::MAX`. + *ppos = (pos + num_written) as i64; + + Ok(num_written) + } +} |