| Message ID | 20240723181024.21168-17-dakr@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Generic `Allocator` support for Rust | expand |
On Tue Jul 23, 2024 at 9:10 PM EEST, Danilo Krummrich wrote: > Currently, we can't implement `FromIterator`. There are a couple of > issues with this trait in the kernel, namely: > > - Rust's specialization feature is unstable. This prevents us to > optimze for the special case where `I::IntoIter` equals `Vec`'s > `IntoIter` type. > - We also can't use `I::IntoIter`'s type ID either to work around this, > since `FromIterator` doesn't require this type to be `'static`. > - `FromIterator::from_iter` does return `Self` instead of > `Result<Self, AllocError>`, hence we can't properly handle allocation > failures. > - Neither `Iterator::collect` nor `FromIterator::from_iter` can handle > additional allocation flags. Well that's a shame, so I guess collecting a Filter or Map is not possible. > > Instead, provide `IntoIter::collect`, such that we can at least convert > `IntoIter` into a `Vec` again. > > Signed-off-by: Danilo Krummrich <dakr@kernel.org> > --- > rust/kernel/alloc/kvec.rs | 80 ++++++++++++++++++++++++++++++++++++++- > 1 file changed, 79 insertions(+), 1 deletion(-) > > diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs > index fbfb755b252d..5c317931e14c 100644 > --- a/rust/kernel/alloc/kvec.rs > +++ b/rust/kernel/alloc/kvec.rs > @@ -2,7 +2,7 @@ > > //! Implementation of [`Vec`]. > > -use super::{AllocError, Allocator, Flags}; > +use super::{flags::*, AllocError, Allocator, Flags}; > use crate::types::Unique; > use core::{ > fmt, > @@ -633,6 +633,84 @@ impl<T, A> IntoIter<T, A> > fn as_raw_mut_slice(&mut self) -> *mut [T] { > ptr::slice_from_raw_parts_mut(self.ptr, self.len) > } > + > + fn into_raw_parts(self) -> (*mut T, NonNull<T>, usize, usize) { > + let me = ManuallyDrop::new(self); > + let ptr = me.ptr; > + let buf = me.buf; > + let len = me.len; > + let cap = me.cap; > + (ptr, buf, len, cap) > + } > + > + /// Same as `Iterator::collect` but specialized for `Vec`'s `IntoIter`. > + /// > + /// Currently, we can't implement `FromIterator`. There are a couple of issues with this trait > + /// in the kernel, namely: > + /// > + /// - Rust's specialization feature is unstable. This prevents us to optimze for the special > + /// case where `I::IntoIter` equals `Vec`'s `IntoIter` type. > + /// - We also can't use `I::IntoIter`'s type ID either to work around this, since `FromIterator` > + /// doesn't require this type to be `'static`. > + /// - `FromIterator::from_iter` does return `Self` instead of `Result<Self, AllocError>`, hence > + /// we can't properly handle allocation failures. > + /// - Neither `Iterator::collect` nor `FromIterator::from_iter` can handle additional allocation > + /// flags. > + /// > + /// Instead, provide `IntoIter::collect`, such that we can at least convert a `IntoIter` into a > + /// `Vec` again. > + /// > + /// Note that `IntoIter::collect` doesn't require `Flags`, since it re-uses the existing backing > + /// buffer. However, this backing buffer may be shrunk to the actual count of elements. > + /// > + /// # Examples > + /// > + /// ``` > + /// let v = kernel::kvec![1, 2, 3]?; > + /// let mut it = v.into_iter(); > + /// > + /// assert_eq!(it.next(), Some(1)); > + /// > + /// let v = it.collect(); > + /// assert_eq!(v, [2, 3]); > + /// > + /// # Ok::<(), Error>(()) > + /// ``` > + pub fn collect(self) -> Vec<T, A> { > + let (mut ptr, buf, len, mut cap) = self.into_raw_parts(); > + let has_advanced = ptr != buf.as_ptr(); > + > + if has_advanced { > + // SAFETY: Copy the contents we have advanced to at the beginning of the buffer. > + // `ptr` is guaranteed to be between `buf` and `buf.add(cap)` and `ptr.add(len)` is > + // guaranteed to be smaller than `buf.add(cap)`. > + unsafe { ptr::copy(ptr, buf.as_ptr(), len) }; > + ptr = buf.as_ptr(); > + } > + > + // This can never fail, `len` is guaranteed to be smaller than `cap`. > + let layout = core::alloc::Layout::array::<T>(len).unwrap(); > + > + // SAFETY: `buf` points to the start of the backing buffer and `len` is guaranteed to be > + // smaller than `cap`. Depending on `alloc` this operation may shrink the buffer or leaves > + // it as it is. > + ptr = match unsafe { A::realloc(Some(buf.cast()), layout, GFP_KERNEL) } { Here you use `GFP_KERNEL` flag directly. Shouldn't this be an argument of `collect` function? > + // If we fail to shrink, which likely can't even happen, continue with the existing > + // buffer. > + Err(_) => ptr, > + Ok(ptr) => { > + cap = len; > + ptr.as_ptr().cast() > + } > + }; > + > + // SAFETY: If the iterator has been advanced, the advanced elements have been copied to > + // the beginning of the buffer and `len` has been adjusted accordingly. `ptr` is guaranteed > + // to point to the start of the backing buffer. `cap` is either the original capacity or, > + // after shrinking the buffer, equal to `len`. `alloc` is guaranteed to be unchanged since > + // `into_iter` has been called on the original `Vec`. > + unsafe { Vec::from_raw_parts(ptr, len, cap) } > + } > } > > impl<T, A> Iterator for IntoIter<T, A> > -- > 2.45.2
On Wed, Jul 24, 2024 at 02:35:46PM +0000, Heghedus Razvan wrote: > On Tue Jul 23, 2024 at 9:10 PM EEST, Danilo Krummrich wrote: > > Currently, we can't implement `FromIterator`. There are a couple of > > issues with this trait in the kernel, namely: > > > > - Rust's specialization feature is unstable. This prevents us to > > optimze for the special case where `I::IntoIter` equals `Vec`'s > > `IntoIter` type. > > - We also can't use `I::IntoIter`'s type ID either to work around this, > > since `FromIterator` doesn't require this type to be `'static`. > > - `FromIterator::from_iter` does return `Self` instead of > > `Result<Self, AllocError>`, hence we can't properly handle allocation > > failures. > > - Neither `Iterator::collect` nor `FromIterator::from_iter` can handle > > additional allocation flags. > Well that's a shame, so I guess collecting a Filter or Map is not possible. Not with the Rust's `FromIterator` trait, unfortunately. However, once we have other collectable data structures in place, we can come up with a kernel compatible version of the `FromIterator` trait and implement against it. > > > > > Instead, provide `IntoIter::collect`, such that we can at least convert > > `IntoIter` into a `Vec` again. > > > > Signed-off-by: Danilo Krummrich <dakr@kernel.org> > > --- > > rust/kernel/alloc/kvec.rs | 80 ++++++++++++++++++++++++++++++++++++++- > > 1 file changed, 79 insertions(+), 1 deletion(-) > > > > diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs > > index fbfb755b252d..5c317931e14c 100644 > > --- a/rust/kernel/alloc/kvec.rs > > +++ b/rust/kernel/alloc/kvec.rs > > @@ -2,7 +2,7 @@ > > > > //! Implementation of [`Vec`]. > > > > -use super::{AllocError, Allocator, Flags}; > > +use super::{flags::*, AllocError, Allocator, Flags}; > > use crate::types::Unique; > > use core::{ > > fmt, > > @@ -633,6 +633,84 @@ impl<T, A> IntoIter<T, A> > > fn as_raw_mut_slice(&mut self) -> *mut [T] { > > ptr::slice_from_raw_parts_mut(self.ptr, self.len) > > } > > + > > + fn into_raw_parts(self) -> (*mut T, NonNull<T>, usize, usize) { > > + let me = ManuallyDrop::new(self); > > + let ptr = me.ptr; > > + let buf = me.buf; > > + let len = me.len; > > + let cap = me.cap; > > + (ptr, buf, len, cap) > > + } > > + > > + /// Same as `Iterator::collect` but specialized for `Vec`'s `IntoIter`. > > + /// > > + /// Currently, we can't implement `FromIterator`. There are a couple of issues with this trait > > + /// in the kernel, namely: > > + /// > > + /// - Rust's specialization feature is unstable. This prevents us to optimze for the special > > + /// case where `I::IntoIter` equals `Vec`'s `IntoIter` type. > > + /// - We also can't use `I::IntoIter`'s type ID either to work around this, since `FromIterator` > > + /// doesn't require this type to be `'static`. > > + /// - `FromIterator::from_iter` does return `Self` instead of `Result<Self, AllocError>`, hence > > + /// we can't properly handle allocation failures. > > + /// - Neither `Iterator::collect` nor `FromIterator::from_iter` can handle additional allocation > > + /// flags. > > + /// > > + /// Instead, provide `IntoIter::collect`, such that we can at least convert a `IntoIter` into a > > + /// `Vec` again. > > + /// > > + /// Note that `IntoIter::collect` doesn't require `Flags`, since it re-uses the existing backing > > + /// buffer. However, this backing buffer may be shrunk to the actual count of elements. > > + /// > > + /// # Examples > > + /// > > + /// ``` > > + /// let v = kernel::kvec![1, 2, 3]?; > > + /// let mut it = v.into_iter(); > > + /// > > + /// assert_eq!(it.next(), Some(1)); > > + /// > > + /// let v = it.collect(); > > + /// assert_eq!(v, [2, 3]); > > + /// > > + /// # Ok::<(), Error>(()) > > + /// ``` > > + pub fn collect(self) -> Vec<T, A> { > > + let (mut ptr, buf, len, mut cap) = self.into_raw_parts(); > > + let has_advanced = ptr != buf.as_ptr(); > > + > > + if has_advanced { > > + // SAFETY: Copy the contents we have advanced to at the beginning of the buffer. > > + // `ptr` is guaranteed to be between `buf` and `buf.add(cap)` and `ptr.add(len)` is > > + // guaranteed to be smaller than `buf.add(cap)`. > > + unsafe { ptr::copy(ptr, buf.as_ptr(), len) }; > > + ptr = buf.as_ptr(); > > + } > > + > > + // This can never fail, `len` is guaranteed to be smaller than `cap`. > > + let layout = core::alloc::Layout::array::<T>(len).unwrap(); > > + > > + // SAFETY: `buf` points to the start of the backing buffer and `len` is guaranteed to be > > + // smaller than `cap`. Depending on `alloc` this operation may shrink the buffer or leaves > > + // it as it is. > > + ptr = match unsafe { A::realloc(Some(buf.cast()), layout, GFP_KERNEL) } { > Here you use `GFP_KERNEL` flag directly. Shouldn't this be an argument of `collect` function? Even though we only ever ask the allocator to shrink the buffer (or keep it as it is), it should be, good catch! > > > + // If we fail to shrink, which likely can't even happen, continue with the existing > > + // buffer. > > + Err(_) => ptr, > > + Ok(ptr) => { > > + cap = len; > > + ptr.as_ptr().cast() > > + } > > + }; > > + > > + // SAFETY: If the iterator has been advanced, the advanced elements have been copied to > > + // the beginning of the buffer and `len` has been adjusted accordingly. `ptr` is guaranteed > > + // to point to the start of the backing buffer. `cap` is either the original capacity or, > > + // after shrinking the buffer, equal to `len`. `alloc` is guaranteed to be unchanged since > > + // `into_iter` has been called on the original `Vec`. > > + unsafe { Vec::from_raw_parts(ptr, len, cap) } > > + } > > } > > > > impl<T, A> Iterator for IntoIter<T, A> > > -- > > 2.45.2 > >
diff --git a/rust/kernel/alloc/kvec.rs b/rust/kernel/alloc/kvec.rs index fbfb755b252d..5c317931e14c 100644 --- a/rust/kernel/alloc/kvec.rs +++ b/rust/kernel/alloc/kvec.rs @@ -2,7 +2,7 @@ //! Implementation of [`Vec`]. -use super::{AllocError, Allocator, Flags}; +use super::{flags::*, AllocError, Allocator, Flags}; use crate::types::Unique; use core::{ fmt, @@ -633,6 +633,84 @@ impl<T, A> IntoIter<T, A> fn as_raw_mut_slice(&mut self) -> *mut [T] { ptr::slice_from_raw_parts_mut(self.ptr, self.len) } + + fn into_raw_parts(self) -> (*mut T, NonNull<T>, usize, usize) { + let me = ManuallyDrop::new(self); + let ptr = me.ptr; + let buf = me.buf; + let len = me.len; + let cap = me.cap; + (ptr, buf, len, cap) + } + + /// Same as `Iterator::collect` but specialized for `Vec`'s `IntoIter`. + /// + /// Currently, we can't implement `FromIterator`. There are a couple of issues with this trait + /// in the kernel, namely: + /// + /// - Rust's specialization feature is unstable. This prevents us to optimze for the special + /// case where `I::IntoIter` equals `Vec`'s `IntoIter` type. + /// - We also can't use `I::IntoIter`'s type ID either to work around this, since `FromIterator` + /// doesn't require this type to be `'static`. + /// - `FromIterator::from_iter` does return `Self` instead of `Result<Self, AllocError>`, hence + /// we can't properly handle allocation failures. + /// - Neither `Iterator::collect` nor `FromIterator::from_iter` can handle additional allocation + /// flags. + /// + /// Instead, provide `IntoIter::collect`, such that we can at least convert a `IntoIter` into a + /// `Vec` again. + /// + /// Note that `IntoIter::collect` doesn't require `Flags`, since it re-uses the existing backing + /// buffer. However, this backing buffer may be shrunk to the actual count of elements. + /// + /// # Examples + /// + /// ``` + /// let v = kernel::kvec![1, 2, 3]?; + /// let mut it = v.into_iter(); + /// + /// assert_eq!(it.next(), Some(1)); + /// + /// let v = it.collect(); + /// assert_eq!(v, [2, 3]); + /// + /// # Ok::<(), Error>(()) + /// ``` + pub fn collect(self) -> Vec<T, A> { + let (mut ptr, buf, len, mut cap) = self.into_raw_parts(); + let has_advanced = ptr != buf.as_ptr(); + + if has_advanced { + // SAFETY: Copy the contents we have advanced to at the beginning of the buffer. + // `ptr` is guaranteed to be between `buf` and `buf.add(cap)` and `ptr.add(len)` is + // guaranteed to be smaller than `buf.add(cap)`. + unsafe { ptr::copy(ptr, buf.as_ptr(), len) }; + ptr = buf.as_ptr(); + } + + // This can never fail, `len` is guaranteed to be smaller than `cap`. + let layout = core::alloc::Layout::array::<T>(len).unwrap(); + + // SAFETY: `buf` points to the start of the backing buffer and `len` is guaranteed to be + // smaller than `cap`. Depending on `alloc` this operation may shrink the buffer or leaves + // it as it is. + ptr = match unsafe { A::realloc(Some(buf.cast()), layout, GFP_KERNEL) } { + // If we fail to shrink, which likely can't even happen, continue with the existing + // buffer. + Err(_) => ptr, + Ok(ptr) => { + cap = len; + ptr.as_ptr().cast() + } + }; + + // SAFETY: If the iterator has been advanced, the advanced elements have been copied to + // the beginning of the buffer and `len` has been adjusted accordingly. `ptr` is guaranteed + // to point to the start of the backing buffer. `cap` is either the original capacity or, + // after shrinking the buffer, equal to `len`. `alloc` is guaranteed to be unchanged since + // `into_iter` has been called on the original `Vec`. + unsafe { Vec::from_raw_parts(ptr, len, cap) } + } } impl<T, A> Iterator for IntoIter<T, A>
Currently, we can't implement `FromIterator`. There are a couple of issues with this trait in the kernel, namely: - Rust's specialization feature is unstable. This prevents us to optimze for the special case where `I::IntoIter` equals `Vec`'s `IntoIter` type. - We also can't use `I::IntoIter`'s type ID either to work around this, since `FromIterator` doesn't require this type to be `'static`. - `FromIterator::from_iter` does return `Self` instead of `Result<Self, AllocError>`, hence we can't properly handle allocation failures. - Neither `Iterator::collect` nor `FromIterator::from_iter` can handle additional allocation flags. Instead, provide `IntoIter::collect`, such that we can at least convert `IntoIter` into a `Vec` again. Signed-off-by: Danilo Krummrich <dakr@kernel.org> --- rust/kernel/alloc/kvec.rs | 80 ++++++++++++++++++++++++++++++++++++++- 1 file changed, 79 insertions(+), 1 deletion(-)