Re: [PATCH] rust: less allocation in CString::try_from

[Onur <work@onurozkan.dev>]

On Mon, 15 Sep 2025 09:26:00 +0200
Alice Ryhl <aliceryhl@google.com> wrote:

> On Mon, Sep 15, 2025 at 8:54 AM Onur Özkan <work@onurozkan.dev> wrote:
> >
> > Allocates buffer with the correct capacity upfront by
> > using the length of the `CStr` to avoid extra and unnecessary
> > re-allocation when converting from `CStr` to `CString`.
> >
> > Signed-off-by: Onur Özkan <work@onurozkan.dev>
> > ---
> >  rust/kernel/str.rs | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/rust/kernel/str.rs b/rust/kernel/str.rs
> > index 6c892550c0ba..98d41d995e45 100644
> > --- a/rust/kernel/str.rs
> > +++ b/rust/kernel/str.rs
> > @@ -946,9 +946,10 @@ impl<'a> TryFrom<&'a CStr> for CString {
> >      type Error = AllocError;
> >
> >      fn try_from(cstr: &'a CStr) -> Result<CString, AllocError> {
> > -        let mut buf = KVec::new();
> > +        let bytes = cstr.to_bytes_with_nul();
> >
> > -        buf.extend_from_slice(cstr.to_bytes_with_nul(),
> > GFP_KERNEL)?;
> > +        let mut buf = KVec::with_capacity(bytes.len(),
> > GFP_KERNEL)?;
> > +        buf.extend_from_slice(bytes, GFP_KERNEL)?;
> 
> I don't think this changes the number of allocations. KVec::new() does
> not allocate.
> 
> Alice

Good to know, thanks!

Onur