linux-kernel - Re: [RFC PATCH 1/2] rust: add initial scatterlist bindings

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Message-Id: <AC0FC018-4440-4027-9943-12FFB481AA6E@collabora.com>
Date: Mon, 12 May 2025 17:01:45 -0300
From: Daniel Almeida <daniel.almeida@...labora.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Abdiel Janulgue <abdiel.janulgue@...il.com>,
 dakr@...nel.org,
 lyude@...hat.com,
 Miguel Ojeda <ojeda@...nel.org>,
 Alex Gaynor <alex.gaynor@...il.com>,
 Boqun Feng <boqun.feng@...il.com>,
 Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <benno.lossin@...ton.me>,
 Andreas Hindborg <a.hindborg@...nel.org>,
 Alice Ryhl <aliceryhl@...gle.com>,
 Trevor Gross <tmgross@...ch.edu>,
 Valentin Obst <kernel@...entinobst.de>,
 open list <linux-kernel@...r.kernel.org>,
 Marek Szyprowski <m.szyprowski@...sung.com>,
 Robin Murphy <robin.murphy@....com>,
 airlied@...hat.com,
 rust-for-linux@...r.kernel.org,
 "open list:DMA MAPPING HELPERS" <iommu@...ts.linux.dev>,
 Petr Tesarik <petr@...arici.cz>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Herbert Xu <herbert@...dor.apana.org.au>,
 Sui Jingfeng <sui.jingfeng@...ux.dev>,
 Randy Dunlap <rdunlap@...radead.org>,
 Michael Kelley <mhklinux@...look.com>
Subject: Re: [RFC PATCH 1/2] rust: add initial scatterlist bindings

Hi Jason,

>> +
>> +    /// Map this scatter-gather table describing a buffer for DMA.
>> +    pub fn dma_map(&mut self, dir: DmaDataDirection) -> Result {
>> +        // SAFETY: Invariants on `Device` and `SGTable` ensures that the `self.dev` and `self.sg`
>> +        // pointers are valid.
>> +        let ret = unsafe {
>> +            bindings::dma_map_sgtable(
>> +                self.dev.as_raw(),
>> +                self.sg.as_raw(),
> 
> Can't call this function on an unbound driver, didn't someone add
> special types for this recently?

JFYI: I think that the “Bound” state is still WIP and not upstream yet.

> 
>> +impl Drop for DeviceSGTable {
>> +    fn drop(&mut self) {
>> +        if self.dir != DmaDataDirection::DmaNone {
>> +            // SAFETY: Invariants on `Device` and `SGTable` ensures that the `self.dev` and `self.sg`
>> +            // pointers are valid.
> 
> Wrong safety statement, Device must be on a bound driver to call this
> function, a valid pointer (eg device refcount) is not enough.
> 
> Jason


— Daniel