linux-kernel - Re: [PATCH v2 03/14] rust: str: introduce `NullBorrowFormatter`

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <877c0gjomz.fsf@kernel.org>
Date: Thu, 10 Jul 2025 13:01:24 +0200
From: Andreas Hindborg <a.hindborg@...nel.org>
To: "Alice Ryhl" <aliceryhl@...gle.com>
Cc: "Boqun Feng" <boqun.feng@...il.com>,  "Miguel Ojeda" <ojeda@...nel.org>,
  "Alex Gaynor" <alex.gaynor@...il.com>,  "Gary Guo" <gary@...yguo.net>,
  Björn Roy Baron <bjorn3_gh@...tonmail.com>,  "Benno
 Lossin"
 <lossin@...nel.org>,  "Trevor Gross" <tmgross@...ch.edu>,  "Danilo
 Krummrich" <dakr@...nel.org>,  "Jens Axboe" <axboe@...nel.dk>,
  <linux-block@...r.kernel.org>,  <rust-for-linux@...r.kernel.org>,
  <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 03/14] rust: str: introduce `NullBorrowFormatter`

"Alice Ryhl" <aliceryhl@...gle.com> writes:

> On Wed, Jul 09, 2025 at 05:49:57PM +0200, Andreas Hindborg wrote:
>> "Alice Ryhl" <aliceryhl@...gle.com> writes:
>>
>> > On Tue, Jul 08, 2025 at 09:44:58PM +0200, Andreas Hindborg wrote:
>> >> Add `NullBorrowFormatter`, a formatter that writes a null terminated string
>> >> to an array or slice buffer. Because this type needs to manage the trailing
>> >> null marker, the existing formatters cannot be used to implement this type.
>> >>
>> >> Signed-off-by: Andreas Hindborg <a.hindborg@...nel.org>
>> >> ---
>> >>  rust/kernel/str.rs | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>> >>  1 file changed, 59 insertions(+)
>> >>
>> >> diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
>> >> index 78b2f95eb3171..05d79cf40c201 100644
>> >> --- a/rust/kernel/str.rs
>> >> +++ b/rust/kernel/str.rs
>> >> @@ -860,6 +860,65 @@ fn deref_mut(&mut self) -> &mut Self::Target {
>> >>      }
>> >>  }
>> >>
>> >> +/// A mutable reference to a byte buffer where a string can be written into.
>> >> +///
>> >> +/// The buffer will be automatically null terminated after the last written character.
>> >> +///
>> >> +/// # Invariants
>> >> +///
>> >> +/// `buffer` is always null terminated.
>> >> +pub(crate) struct NullBorrowFormatter<'a> {
>> >> +    buffer: &'a mut [u8],
>> >> +    pos: usize,
>> >> +}
>> >
>> > Do you need `pos`? Often I see this kind of code subslice `buffer`
>> > instead.
>>
>> How would that work? Can I move the start index of `buffer` in some way
>> without an unsafe block?
>
> Yes. I think this will work:
>
> let buffer = mem::take(&mut self.buffer);
> self.buffer = &mut buffer[pos..];
>
> Temporarily storing an empty slice avoids lifetime issues.

Ah, that is neat.


Best regards,
Andreas Hindborg