[PATCH v4 0/4] rust: alloc: split `Vec::set_len` into `Vec::{inc,dec}_len`

Tamir Duberstein
2025-04-16T17:15:50Z

This series is the product of a discussion[0] on the safety requirements
of `set_len`.

Link: https://lore.kernel.org/all/20250315154436.65065-1-dakr@kernel.org/ [0]
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
---
Changes in v4:
- Rebase on rust/alloc-next to resolve conflict with "rust: alloc: use
`spare_capacity_mut` to reduce unsafe".
- Link: https://lore.kernel.org/all/20250318-vec-push-use-spare-v3-1-68741671d1af@gmail.com/
- Link to v3: https://lore.kernel.org/r/20250407-vec-set-len-v3-0-c5da0d03216e@gmail.com

Changes in v3:
- Fix compilation (s/ptr/tail/) in "refactor `Vec::truncate` using
`dec_len`".
- Fix grammar and s/alloc/realloc/ in a safety comment touched by "rust:
alloc: add Vec::len() <= Vec::capacity invariant".
- Use `if let`. (Alice Ryhl).
- Avoid mutable reference after `drop_in_place`. (Alice Ryhl).
- Rebase on rust/alloc-next.
- Remove dependency on the `Vec::truncate` series which has been merged.
- Link to v2: https://lore.kernel.org/r/20250318-vec-set-len-v2-0-293d55f82d18@gmail.com

Changes in v2:
- Avoid overflow in `set_len`. (Benno Lossin)
- Explained `CString::try_from_fmt` usage of `set_len`. (Benno Lossin,
Miguel Ojeda, Alice Ryhl)
- Added missing SoB. (Alice Ryhl)
- Prepend a patch documenting `Vec::len() <= Vec::capacity()` invariant.
- Add a patch rewriting `Vec::truncate` in terms of `Vec::dec_len`.
- Link to v1: https://lore.kernel.org/r/20250316-vec-set-len-v1-0-60f98a28723f@gmail.com

---
Tamir Duberstein (4):
rust: alloc: add Vec::len() <= Vec::capacity invariant
rust: alloc: add `Vec::dec_len`
rust: alloc: refactor `Vec::truncate` using `dec_len`
rust: alloc: replace `Vec::set_len` with `inc_len`

rust/kernel/alloc/kvec.rs | 81 +++++++++++++++++++++++++++--------------------
rust/kernel/str.rs | 2 +-
rust/kernel/uaccess.rs | 2 +-
3 files changed, 49 insertions(+), 36 deletions(-)
---
base-commit: c3152988c047a7b6abb10d4dc5e24fafbabe8b7e
change-id: 20250316-vec-set-len-99be6cc48374

Best regards,
--
Tamir Duberstein <tamird@gmail.com>