I've been using the linked list cursor for a few different things, and I
find it inconvenient to use because all of the functions have signatures
along the lines of `Self -> Option<Self>`. The root cause of these
signatures is that the cursor points *at* an element, rather than
*between* two elements.
Thus, change the cursor API to point between two elements. This is
inspired by the stdlib linked list (well, really by this guy [1]), which
also uses cursors that point between elements.
The `peek_next` method returns a helper that lets you look at and
optionally remove the element, as one common use-case of cursors is to
iterate a list to look for an element, then remove that element.
For many of the methods, this will reduce how many we need since they
now just need a prev/next method, instead of the current state where you
may end up needing all of curr/prev/next. Also, if we decide to add a
function for splitting a list into two lists at the cursor, then a
cursor that points between elements is exactly what makes the most
sense.
Another advantage is that this means you can now have a cursor into an
empty list.
Link: https://rust-unofficial.github.io/too-many-lists/sixth-cursors-intro.html [1]
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
rust/kernel/list.rs | 401 +++++++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 347 insertions(+), 54 deletions(-)
diff --git a/rust/kernel/list.rs b/rust/kernel/list.rs
index 97b3599b7207..239cf74b84f5 100644
--- a/rust/kernel/list.rs
+++ b/rust/kernel/list.rs
@@ -483,17 +483,21 @@ pub fn push_all_back(&mut self, other: &mut List<T, ID>) {
other.first = ptr::null_mut();
}
- /// Returns a cursor to the first element of the list.
- ///
- /// If the list is empty, this returns `None`.
- pub fn cursor_front(&mut self) -> Option<Cursor<'_, T, ID>> {
- if self.first.is_null() {
- None
- } else {
- Some(Cursor {
- current: self.first,
- list: self,
- })
+ /// Returns a cursor that points before the first element of the list.
+ pub fn cursor_front(&mut self) -> Cursor<'_, T, ID> {
+ // INVARIANT: `self.first` is in this list.
+ Cursor {
+ next: self.first,
+ list: self,
+ }
+ }
+
+ /// Returns a cursor that points after the last element in the list.
+ pub fn cursor_back(&mut self) -> Cursor<'_, T, ID> {
+ // INVARIANT: `next` is allowed to be null.
+ Cursor {
+ next: core::ptr::null_mut(),
+ list: self,
}
}
@@ -573,69 +577,358 @@ fn next(&mut self) -> Option<ArcBorrow<'a, T>> {
/// A cursor into a [`List`].
///
+/// A cursor always rests between two elements in the list. This means that a cursor has a previous
+/// and next element, but no current element. It also means that it's possible to have a cursor
+/// into an empty list.
+///
+/// # Examples
+///
+/// ```
+/// use kernel::prelude::*;
+/// use kernel::list::{List, ListArc, ListLinks};
+///
+/// #[pin_data]
+/// struct ListItem {
+/// value: u32,
+/// #[pin]
+/// links: ListLinks,
+/// }
+///
+/// impl ListItem {
+/// fn new(value: u32) -> Result<ListArc<Self>> {
+/// ListArc::pin_init(try_pin_init!(Self {
+/// value,
+/// links <- ListLinks::new(),
+/// }), GFP_KERNEL)
+/// }
+/// }
+///
+/// kernel::list::impl_has_list_links! {
+/// impl HasListLinks<0> for ListItem { self.links }
+/// }
+/// kernel::list::impl_list_arc_safe! {
+/// impl ListArcSafe<0> for ListItem { untracked; }
+/// }
+/// kernel::list::impl_list_item! {
+/// impl ListItem<0> for ListItem { using ListLinks; }
+/// }
+///
+/// // Use a cursor to remove the first element with the given value.
+/// fn remove_first(list: &mut List<ListItem>, value: u32) -> Option<ListArc<ListItem>> {
+/// let mut cursor = list.cursor_front();
+/// while let Some(next) = cursor.peek_next() {
+/// if next.value == value {
+/// return Some(next.remove());
+/// }
+/// cursor.move_next();
+/// }
+/// None
+/// }
+///
+/// // Use a cursor to remove the last element with the given value.
+/// fn remove_last(list: &mut List<ListItem>, value: u32) -> Option<ListArc<ListItem>> {
+/// let mut cursor = list.cursor_back();
+/// while let Some(prev) = cursor.peek_prev() {
+/// if prev.value == value {
+/// return Some(prev.remove());
+/// }
+/// cursor.move_prev();
+/// }
+/// None
+/// }
+///
+/// // Use a cursor to remove all elements with the given value. The removed elements are moved to
+/// // a new list.
+/// fn remove_all(list: &mut List<ListItem>, value: u32) -> List<ListItem> {
+/// let mut out = List::new();
+/// let mut cursor = list.cursor_front();
+/// while let Some(next) = cursor.peek_next() {
+/// if next.value == value {
+/// out.push_back(next.remove());
+/// } else {
+/// cursor.move_next();
+/// }
+/// }
+/// out
+/// }
+///
+/// // Use a cursor to insert a value at a specific index. Returns an error if the index is out of
+/// // bounds.
+/// fn insert_at(list: &mut List<ListItem>, new: ListArc<ListItem>, idx: usize) -> Result {
+/// let mut cursor = list.cursor_front();
+/// for _ in 0..idx {
+/// if !cursor.move_next() {
+/// return Err(EINVAL);
+/// }
+/// }
+/// cursor.insert_next(new);
+/// Ok(())
+/// }
+///
+/// // Merge two sorted lists into a single sorted list.
+/// fn merge_sorted(list: &mut List<ListItem>, merge: List<ListItem>) {
+/// let mut cursor = list.cursor_front();
+/// for to_insert in merge {
+/// while let Some(next) = cursor.peek_next() {
+/// if to_insert.value < next.value {
+/// break;
+/// }
+/// cursor.move_next();
+/// }
+/// cursor.insert_prev(to_insert);
+/// }
+/// }
+///
+/// let mut list = List::new();
+/// list.push_back(ListItem::new(14)?);
+/// list.push_back(ListItem::new(12)?);
+/// list.push_back(ListItem::new(10)?);
+/// list.push_back(ListItem::new(12)?);
+/// list.push_back(ListItem::new(15)?);
+/// list.push_back(ListItem::new(14)?);
+/// assert_eq!(remove_all(&mut list, 12).iter().count(), 2);
+/// // [14, 10, 15, 14]
+/// assert!(remove_first(&mut list, 14).is_some());
+/// // [10, 15, 14]
+/// insert_at(&mut list, ListItem::new(12)?, 2)?;
+/// // [10, 15, 12, 14]
+/// assert!(remove_last(&mut list, 15).is_some());
+/// // [10, 12, 14]
+///
+/// let mut list2 = List::new();
+/// list2.push_back(ListItem::new(11)?);
+/// list2.push_back(ListItem::new(13)?);
+/// merge_sorted(&mut list, list2);
+///
+/// let mut items = list.into_iter();
+/// assert_eq!(items.next().unwrap().value, 10);
+/// assert_eq!(items.next().unwrap().value, 11);
+/// assert_eq!(items.next().unwrap().value, 12);
+/// assert_eq!(items.next().unwrap().value, 13);
+/// assert_eq!(items.next().unwrap().value, 14);
+/// assert!(items.next().is_none());
+/// # Result::<(), Error>::Ok(())
+/// ```
+///
/// # Invariants
///
-/// The `current` pointer points a value in `list`.
+/// The `next` pointer is null or points a value in `list`.
pub struct Cursor<'a, T: ?Sized + ListItem<ID>, const ID: u64 = 0> {
- current: *mut ListLinksFields,
list: &'a mut List<T, ID>,
+ /// Points at the element after this cursor, or null if the cursor is after the last element.
+ next: *mut ListLinksFields,
}
impl<'a, T: ?Sized + ListItem<ID>, const ID: u64> Cursor<'a, T, ID> {
- /// Access the current element of this cursor.
- pub fn current(&self) -> ArcBorrow<'_, T> {
- // SAFETY: The `current` pointer points a value in the list.
- let me = unsafe { T::view_value(ListLinks::from_fields(self.current)) };
- // SAFETY:
- // * All values in a list are stored in an `Arc`.
- // * The value cannot be removed from the list for the duration of the lifetime annotated
- // on the returned `ArcBorrow`, because removing it from the list would require mutable
- // access to the cursor or the list. However, the `ArcBorrow` holds an immutable borrow
- // on the cursor, which in turn holds a mutable borrow on the list, so any such
- // mutable access requires first releasing the immutable borrow on the cursor.
- // * Values in a list never have a `UniqueArc` reference, because the list has a `ListArc`
- // reference, and `UniqueArc` references must be unique.
- unsafe { ArcBorrow::from_raw(me) }
+ /// Returns a pointer to the element before the cursor.
+ ///
+ /// Returns null if there is no element before the cursor.
+ fn prev_ptr(&self) -> *mut ListLinksFields {
+ let mut next = self.next;
+ let first = self.list.first;
+ if next == first {
+ // We are before the first element.
+ return core::ptr::null_mut();
+ }
+
+ if next.is_null() {
+ // We are after the last element, so we need a pointer to the last element, which is
+ // the same as `(*first).prev`.
+ next = first;
+ }
+
+ // SAFETY: `next` can't be null, because then `first` must also be null, but in that case
+ // we would have exited at the `next == first` check. Thus, `next` is an element in the
+ // list, so we can access its `prev` pointer.
+ unsafe { (*next).prev }
}
- /// Move the cursor to the next element.
- pub fn next(self) -> Option<Cursor<'a, T, ID>> {
- // SAFETY: The `current` field is always in a list.
- let next = unsafe { (*self.current).next };
+ /// Access the element after this cursor.
+ pub fn peek_next(&mut self) -> Option<CursorPeek<'_, 'a, T, true, ID>> {
+ if self.next.is_null() {
+ return None;
+ }
+
+ // INVARIANT:
+ // * We just checked that `self.next` is non-null, so it must be in `self.list`.
+ // * `ptr` is equal to `self.next`.
+ Some(CursorPeek {
+ ptr: self.next,
+ cursor: self,
+ })
+ }
+
+ /// Access the element before this cursor.
+ pub fn peek_prev(&mut self) -> Option<CursorPeek<'_, 'a, T, false, ID>> {
+ let prev = self.prev_ptr();
+
+ if prev.is_null() {
+ return None;
+ }
+
+ // INVARIANT:
+ // * We just checked that `prev` is non-null, so it must be in `self.list`.
+ // * `self.prev_ptr()` never returns `self.next`.
+ Some(CursorPeek {
+ ptr: prev,
+ cursor: self,
+ })
+ }
+
+ /// Move the cursor one element forward.
+ ///
+ /// If the cursor is after the last element, then this call does nothing. This call returns
+ /// `true` if the cursor's position was changed.
+ pub fn move_next(&mut self) -> bool {
+ if self.next.is_null() {
+ return false;
+ }
+
+ // SAFETY: `self.next` is an element in the list and we borrow the list mutably, so we can
+ // access the `next` field.
+ let mut next = unsafe { (*self.next).next };
if next == self.list.first {
- None
- } else {
- // INVARIANT: Since `self.current` is in the `list`, its `next` pointer is also in the
- // `list`.
- Some(Cursor {
- current: next,
- list: self.list,
- })
+ next = core::ptr::null_mut();
}
+
+ // INVARIANT: `next` is either null or the next element after an element in the list.
+ self.next = next;
+ true
}
- /// Move the cursor to the previous element.
- pub fn prev(self) -> Option<Cursor<'a, T, ID>> {
- // SAFETY: The `current` field is always in a list.
- let prev = unsafe { (*self.current).prev };
+ /// Move the cursor one element backwards.
+ ///
+ /// If the cursor is before the first element, then this call does nothing. This call returns
+ /// `true` if the cursor's position was changed.
+ pub fn move_prev(&mut self) -> bool {
+ if self.next == self.list.first {
+ return false;
+ }
+
+ // INVARIANT: `prev_ptr()` always returns a pointer that is null or in the list.
+ self.next = self.prev_ptr();
+ true
+ }
- if self.current == self.list.first {
- None
+ /// Inserts an element where the cursor is pointing and get a pointer to the new element.
+ fn insert_inner(&mut self, item: ListArc<T, ID>) -> *mut ListLinksFields {
+ let ptr = if self.next.is_null() {
+ self.list.first
} else {
- // INVARIANT: Since `self.current` is in the `list`, its `prev` pointer is also in the
- // `list`.
- Some(Cursor {
- current: prev,
- list: self.list,
- })
+ self.next
+ };
+ // SAFETY:
+ // * `ptr` is an element in the list or null.
+ // * if `ptr` is null, then `self.list.first` is null so the list is empty.
+ let item = unsafe { self.list.insert_inner(item, ptr) };
+ if self.next == self.list.first {
+ // INVARIANT: We just inserted `item`, so it's a member of list.
+ self.list.first = item;
}
+ item
+ }
+
+ /// Insert an element at this cursor's location.
+ pub fn insert(self, item: ListArc<T, ID>) {
+ // This is identical to `insert_prev`, but consumes the cursor. This is helpful because it
+ // reduces confusion when the last operation on the cursor is an insertion; in that case,
+ // you just want to insert the element at the cursor, and it is confusing that the call
+ // involves the word prev or next.
+ self.insert_inner(item);
+ }
+
+ /// Inserts an element after this cursor.
+ ///
+ /// After insertion, the new element will be after the cursor.
+ pub fn insert_next(&mut self, item: ListArc<T, ID>) {
+ self.next = self.insert_inner(item);
}
- /// Remove the current element from the list.
+ /// Inserts an element before this cursor.
+ ///
+ /// After insertion, the new element will be before the cursor.
+ pub fn insert_prev(&mut self, item: ListArc<T, ID>) {
+ self.insert_inner(item);
+ }
+
+ /// Remove the next element from the list.
+ pub fn remove_next(&mut self) -> Option<ListArc<T, ID>> {
+ self.peek_next().map(|v| v.remove())
+ }
+
+ /// Remove the previous element from the list.
+ pub fn remove_prev(&mut self) -> Option<ListArc<T, ID>> {
+ self.peek_prev().map(|v| v.remove())
+ }
+}
+
+/// References the element in the list next to the cursor.
+///
+/// # Invariants
+///
+/// * `ptr` is an element in `self.cursor.list`.
+/// * `ISNEXT == (self.ptr == self.cursor.next)`.
+pub struct CursorPeek<'a, 'b, T: ?Sized + ListItem<ID>, const ISNEXT: bool, const ID: u64> {
+ cursor: &'a mut Cursor<'b, T, ID>,
+ ptr: *mut ListLinksFields,
+}
+
+impl<'a, 'b, T: ?Sized + ListItem<ID>, const ISNEXT: bool, const ID: u64>
+ CursorPeek<'a, 'b, T, ISNEXT, ID>
+{
+ /// Remove the element from the list.
pub fn remove(self) -> ListArc<T, ID> {
- // SAFETY: The `current` pointer always points at a member of the list.
- unsafe { self.list.remove_internal(self.current) }
+ if ISNEXT {
+ self.cursor.move_next();
+ }
+
+ // INVARIANT: `self.ptr` is not equal to `self.cursor.next` due to the above `move_next`
+ // call.
+ // SAFETY: By the type invariants of `Self`, `next` is not null, so `next` is an element of
+ // `self.cursor.list` by the type invariants of `Cursor`.
+ unsafe { self.cursor.list.remove_internal(self.ptr) }
+ }
+
+ /// Access this value as an [`ArcBorrow`].
+ pub fn arc(&self) -> ArcBorrow<'_, T> {
+ // SAFETY: `self.ptr` points at an element in `self.cursor.list`.
+ let me = unsafe { T::view_value(ListLinks::from_fields(self.ptr)) };
+ // SAFETY:
+ // * All values in a list are stored in an `Arc`.
+ // * The value cannot be removed from the list for the duration of the lifetime annotated
+ // on the returned `ArcBorrow`, because removing it from the list would require mutable
+ // access to the `CursorPeek`, the `Cursor` or the `List`. However, the `ArcBorrow` holds
+ // an immutable borrow on the `CursorPeek`, which in turn holds a mutable borrow on the
+ // `Cursor`, which in turn holds a mutable borrow on the `List`, so any such mutable
+ // access requires first releasing the immutable borrow on the `CursorPeek`.
+ // * Values in a list never have a `UniqueArc` reference, because the list has a `ListArc`
+ // reference, and `UniqueArc` references must be unique.
+ unsafe { ArcBorrow::from_raw(me) }
+ }
+}
+
+impl<'a, 'b, T: ?Sized + ListItem<ID>, const ISNEXT: bool, const ID: u64> core::ops::Deref
+ for CursorPeek<'a, 'b, T, ISNEXT, ID>
+{
+ // If you change the `ptr` field to have type `ArcBorrow<'a, T>`, it might seem like you could
+ // get rid of the `CursorPeek::arc` method and change the deref target to `ArcBorrow<'a, T>`.
+ // However, that doesn't work because 'a is too long. You could obtain an `ArcBorrow<'a, T>`
+ // and then call `CursorPeek::remove` without giving up the `ArcBorrow<'a, T>`, which would be
+ // unsound.
+ type Target = T;
+
+ fn deref(&self) -> &T {
+ // SAFETY: `self.ptr` points at an element in `self.cursor.list`.
+ let me = unsafe { T::view_value(ListLinks::from_fields(self.ptr)) };
+
+ // SAFETY: The value cannot be removed from the list for the duration of the lifetime
+ // annotated on the returned `&T`, because removing it from the list would require mutable
+ // access to the `CursorPeek`, the `Cursor` or the `List`. However, the `&T` holds an
+ // immutable borrow on the `CursorPeek`, which in turn holds a mutable borrow on the
+ // `Cursor`, which in turn holds a mutable borrow on the `List`, so any such mutable access
+ // requires first releasing the immutable borrow on the `CursorPeek`.
+ unsafe { &*me }
}
}
--
2.48.1.362.g079036d154-googHi Alice,
kernel test robot noticed the following build errors:
[auto build test ERROR on ceff0757f5dafb5be5205988171809c877b1d3e3]
url: https://github.com/intel-lab-lkp/linux/commits/Alice-Ryhl/rust-list-extract-common-code-for-insertion/20250201-041918
base: ceff0757f5dafb5be5205988171809c877b1d3e3
patch link: https://lore.kernel.org/r/20250131-cursor-between-v6-2-603bdc7d4449%40google.com
patch subject: [PATCH v6 2/2] rust: list: make the cursor point between elements
config: x86_64-rhel-9.4-rust (https://download.01.org/0day-ci/archive/20250201/202502012009.gHmXhGHi-lkp@intel.com/config)
compiler: clang version 19.1.3 (https://github.com/llvm/llvm-project ab51eccf88f5321e7c60591c5546b254b6afab99)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250201/202502012009.gHmXhGHi-lkp@intel.com/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202502012009.gHmXhGHi-lkp@intel.com/
All errors (new ones prefixed by >>):
In file included from arch/x86/kernel/asm-offsets.c:14:
In file included from include/linux/suspend.h:5:
In file included from include/linux/swap.h:9:
In file included from include/linux/memcontrol.h:21:
In file included from include/linux/mm.h:2223:
include/linux/vmstat.h:504:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
504 | return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
| ~~~~~~~~~~~~~~~~~~~~~ ^
505 | item];
| ~~~~
include/linux/vmstat.h:511:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
511 | return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
| ~~~~~~~~~~~~~~~~~~~~~ ^
512 | NR_VM_NUMA_EVENT_ITEMS +
| ~~~~~~~~~~~~~~~~~~~~~~
include/linux/vmstat.h:518:36: warning: arithmetic between different enumeration types ('enum node_stat_item' and 'enum lru_list') [-Wenum-enum-conversion]
518 | return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_"
| ~~~~~~~~~~~ ^ ~~~
include/linux/vmstat.h:524:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
524 | return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
| ~~~~~~~~~~~~~~~~~~~~~ ^
525 | NR_VM_NUMA_EVENT_ITEMS +
| ~~~~~~~~~~~~~~~~~~~~~~
4 warnings generated.
***
*** Rust bindings generator 'bindgen' < 0.69.5 together with libclang >= 19.1
*** may not work due to a bug (https://github.com/rust-lang/rust-bindgen/pull/2824),
*** unless patched (like Debian's).
*** Your bindgen version: 0.65.1
*** Your libclang version: 19.1.3
***
***
*** Please see Documentation/rust/quick-start.rst for details
*** on how to set up the Rust support.
***
In file included from rust/helpers/helpers.c:10:
In file included from rust/helpers/blk.c:3:
In file included from include/linux/blk-mq.h:5:
In file included from include/linux/blkdev.h:9:
In file included from include/linux/blk_types.h:10:
In file included from include/linux/bvec.h:10:
In file included from include/linux/highmem.h:8:
In file included from include/linux/cacheflush.h:5:
In file included from arch/x86/include/asm/cacheflush.h:5:
In file included from include/linux/mm.h:2223:
include/linux/vmstat.h:504:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
504 | return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
| ~~~~~~~~~~~~~~~~~~~~~ ^
505 | item];
| ~~~~
include/linux/vmstat.h:511:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
511 | return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
| ~~~~~~~~~~~~~~~~~~~~~ ^
512 | NR_VM_NUMA_EVENT_ITEMS +
| ~~~~~~~~~~~~~~~~~~~~~~
include/linux/vmstat.h:518:36: warning: arithmetic between different enumeration types ('enum node_stat_item' and 'enum lru_list') [-Wenum-enum-conversion]
518 | return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_"
| ~~~~~~~~~~~ ^ ~~~
include/linux/vmstat.h:524:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
524 | return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
| ~~~~~~~~~~~~~~~~~~~~~ ^
525 | NR_VM_NUMA_EVENT_ITEMS +
| ~~~~~~~~~~~~~~~~~~~~~~
4 warnings generated.
clang diag: include/linux/vmstat.h:504:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
clang diag: include/linux/vmstat.h:511:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
clang diag: include/linux/vmstat.h:518:36: warning: arithmetic between different enumeration types ('enum node_stat_item' and 'enum lru_list') [-Wenum-enum-conversion]
clang diag: include/linux/vmstat.h:524:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
clang diag: include/linux/vmstat.h:504:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
clang diag: include/linux/vmstat.h:511:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
clang diag: include/linux/vmstat.h:518:36: warning: arithmetic between different enumeration types ('enum node_stat_item' and 'enum lru_list') [-Wenum-enum-conversion]
clang diag: include/linux/vmstat.h:524:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
clang diag: include/linux/vmstat.h:504:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
clang diag: include/linux/vmstat.h:511:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
clang diag: include/linux/vmstat.h:518:36: warning: arithmetic between different enumeration types ('enum node_stat_item' and 'enum lru_list') [-Wenum-enum-conversion]
clang diag: include/linux/vmstat.h:524:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
>> error[E0596]: cannot borrow `self` as mutable, as it is not declared as mutable
--> rust/kernel/list.rs:838:9
|
838 | self.insert_inner(item);
| ^^^^ cannot borrow as mutable
|
help: consider changing this to be mutable
|
833 | pub fn insert(mut self, item: ListArc<T, ID>) {
| +++
--
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On Fri, Jan 31, 2025 at 9:16 PM Alice Ryhl <aliceryhl@google.com> wrote:
>
> I've been using the linked list cursor for a few different things, and I
> find it inconvenient to use because all of the functions have signatures
> along the lines of `Self -> Option<Self>`. The root cause of these
> signatures is that the cursor points *at* an element, rather than
> *between* two elements.
>
> Thus, change the cursor API to point between two elements. This is
> inspired by the stdlib linked list (well, really by this guy [1]), which
> also uses cursors that point between elements.
>
> The `peek_next` method returns a helper that lets you look at and
> optionally remove the element, as one common use-case of cursors is to
> iterate a list to look for an element, then remove that element.
>
> For many of the methods, this will reduce how many we need since they
> now just need a prev/next method, instead of the current state where you
> may end up needing all of curr/prev/next. Also, if we decide to add a
> function for splitting a list into two lists at the cursor, then a
> cursor that points between elements is exactly what makes the most
> sense.
>
> Another advantage is that this means you can now have a cursor into an
> empty list.
>
> Link: https://rust-unofficial.github.io/too-many-lists/sixth-cursors-intro.html [1]
> Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
> Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
> Signed-off-by: Alice Ryhl <aliceryhl@google.com>
> + /// Insert an element at this cursor's location.
> + pub fn insert(self, item: ListArc<T, ID>) {
Oops this needs to be `mut self` to compile. Those last minute changes get ya.
Alice
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