Nouveau - Sep 2025 - [PATCH 04/10] gpu: nova-core: Add a slice-buffer (sbuffer) datastructure

On 2025-09-07 at 20:54 +1000, Alice Ryhl <aliceryhl at google.com>
wrote...
> On Wed, Aug 27, 2025 at 06:20:01PM +1000, Alistair Popple wrote:
> > From: Joel Fernandes <joelagnelf at nvidia.com>
> > 
> > A data structure that can be used to write across multiple slices
which
> > may be out of order in memory. This lets SBuffer user correctly and
> > safely write out of memory order, without error-prone tracking of
> > pointers/offsets.
> > 
> >  let mut buf1 = [0u8; 3];
> >  let mut buf2 = [0u8; 5];
> >  let mut sbuffer = SBuffer::new([&mut buf1[..], &mut
buf2[..]]);
> > 
> >  let data = b"hellowo";
> >  let result = sbuffer.write(data);
> > 
> > An internal conversion of gsp.rs to use this resulted in a nice -ve
delta:
> > gsp.rs: 37 insertions(+), 99 deletions(-)
> > 
> > Co-developed-by: Alistair Popple <apopple at nvidia.com>
> > Signed-off-by: Alistair Popple <apopple at nvidia.com>
> > Signed-off-by: Joel Fernandes <joelagnelf at nvidia.com>
> 
> This seems like duplication of the logic in rust/kernel/iov_iter.rs [1].
Conceptually I guess there is some overlap. The thing that's different here
is we don't have any C version of the iovec struct or iov_iter, and AFAICT
[1]
doesn't provide any way of creating one from within Rust code.
> Alice
> 
> [1]: https://lore.kernel.org/r/20250822-iov-iter-v5-0-6ce4819c2977 at
google.com

On Mon Sep 8, 2025 at 8:31 PM JST, Alistair Popple
wrote:
> On 2025-09-07 at 20:54 +1000, Alice Ryhl <aliceryhl at google.com>
wrote...
>> On Wed, Aug 27, 2025 at 06:20:01PM +1000, Alistair Popple wrote:
>> > From: Joel Fernandes <joelagnelf at nvidia.com>
>> > 
>> > A data structure that can be used to write across multiple slices
which
>> > may be out of order in memory. This lets SBuffer user correctly
and
>> > safely write out of memory order, without error-prone tracking of
>> > pointers/offsets.
>> > 
>> >  let mut buf1 = [0u8; 3];
>> >  let mut buf2 = [0u8; 5];
>> >  let mut sbuffer = SBuffer::new([&mut buf1[..], &mut
buf2[..]]);
>> > 
>> >  let data = b"hellowo";
>> >  let result = sbuffer.write(data);
>> > 
>> > An internal conversion of gsp.rs to use this resulted in a nice
-ve delta:
>> > gsp.rs: 37 insertions(+), 99 deletions(-)
>> > 
>> > Co-developed-by: Alistair Popple <apopple at nvidia.com>
>> > Signed-off-by: Alistair Popple <apopple at nvidia.com>
>> > Signed-off-by: Joel Fernandes <joelagnelf at nvidia.com>
>> 
>> This seems like duplication of the logic in rust/kernel/iov_iter.rs
[1].
>
> Conceptually I guess there is some overlap. The thing that's different
here
> is we don't have any C version of the iovec struct or iov_iter, and
AFAICT [1]
> doesn't provide any way of creating one from within Rust code.
Yup, I was about to ask as well - I am not familiar with the C API, but
how can we use it from Rust, using e.g. a pair of slices as the data
source/destination? I see that `struct iovec` also has `__user` marker
for its base, which hints to me that it is not designed to work with
kernel data?