Alexandre Courbot
2025-May-22 05:29 UTC
[PATCH v4 01/20] rust: dma: expose the count and size of CoherentAllocation
On Wed May 21, 2025 at 9:43 PM JST, Boqun Feng wrote:> On Wed, May 21, 2025 at 03:44:56PM +0900, Alexandre Courbot wrote: >> These properties are very useful to have and should be accessible. >> >> Signed-off-by: Alexandre Courbot <acourbot at nvidia.com> >> --- >> rust/kernel/dma.rs | 18 ++++++++++++++++++ >> 1 file changed, 18 insertions(+) >> >> diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs >> index 605e01e35715667f93297fd9ec49d8e7032e0910..2a60eefa47dfc1f836c30ee342e26c6ff3e9b13a 100644 >> --- a/rust/kernel/dma.rs >> +++ b/rust/kernel/dma.rs >> @@ -129,6 +129,10 @@ pub mod attrs { >> // >> // Hence, find a way to revoke the device resources of a `CoherentAllocation`, but not the >> // entire `CoherentAllocation` including the allocated memory itself. >> +// >> +// # Invariants >> +// >> +// The size in bytes of the allocation is equal to `size_of::<T> * count()`. >> pub struct CoherentAllocation<T: AsBytes + FromBytes> { >> dev: ARef<Device>, >> dma_handle: bindings::dma_addr_t, >> @@ -201,6 +205,20 @@ pub fn alloc_coherent( >> CoherentAllocation::alloc_attrs(dev, count, gfp_flags, Attrs(0)) >> } >> >> + /// Returns the number of elements `T` in this allocation. >> + /// >> + /// Note that this is not the size of the allocation in bytes, which is provided by >> + /// [`Self::size`]. >> + pub fn count(&self) -> usize { >> + self.count >> + } >> + >> + /// Returns the size in bytes of this allocation. >> + pub fn size(&self) -> usize { >> + // As per the invariants of `CoherentAllocation`. >> + self.count * core::mem::size_of::<T>() > > I think we need a comment or even an invariant saying this multiply > cannot overflow.I'll add the following invariant: `size_of::<T> * count` fits into a `usize`. and refer to it here. Does it work?
Danilo Krummrich
2025-Jun-02 09:24 UTC
[PATCH v4 01/20] rust: dma: expose the count and size of CoherentAllocation
On Thu, May 22, 2025 at 02:29:35PM +0900, Alexandre Courbot wrote:> On Wed May 21, 2025 at 9:43 PM JST, Boqun Feng wrote: > > On Wed, May 21, 2025 at 03:44:56PM +0900, Alexandre Courbot wrote: > >> These properties are very useful to have and should be accessible. > >> > >> Signed-off-by: Alexandre Courbot <acourbot at nvidia.com> > >> --- > >> rust/kernel/dma.rs | 18 ++++++++++++++++++ > >> 1 file changed, 18 insertions(+) > >> > >> diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs > >> index 605e01e35715667f93297fd9ec49d8e7032e0910..2a60eefa47dfc1f836c30ee342e26c6ff3e9b13a 100644 > >> --- a/rust/kernel/dma.rs > >> +++ b/rust/kernel/dma.rs > >> @@ -129,6 +129,10 @@ pub mod attrs { > >> // > >> // Hence, find a way to revoke the device resources of a `CoherentAllocation`, but not the > >> // entire `CoherentAllocation` including the allocated memory itself. > >> +// > >> +// # Invariants > >> +// > >> +// The size in bytes of the allocation is equal to `size_of::<T> * count()`.As you propose below. "... and does fit into a `usize`" You then need an '// INVARIANT' comment where we actually ensure this, i.e. in Self::alloc_attrs().> >> pub struct CoherentAllocation<T: AsBytes + FromBytes> { > >> dev: ARef<Device>, > >> dma_handle: bindings::dma_addr_t, > >> @@ -201,6 +205,20 @@ pub fn alloc_coherent( > >> CoherentAllocation::alloc_attrs(dev, count, gfp_flags, Attrs(0)) > >> } > >> > >> + /// Returns the number of elements `T` in this allocation. > >> + /// > >> + /// Note that this is not the size of the allocation in bytes, which is provided by > >> + /// [`Self::size`]. > >> + pub fn count(&self) -> usize { > >> + self.count > >> + } > >> + > >> + /// Returns the size in bytes of this allocation. > >> + pub fn size(&self) -> usize { > >> + // As per the invariants of `CoherentAllocation`."The type invariant of `Self` guarantees that [...]" or similar.> >> + self.count * core::mem::size_of::<T>() > > > > I think we need a comment or even an invariant saying this multiply > > cannot overflow. > > I'll add the following invariant: > > `size_of::<T> * count` fits into a `usize`. > > and refer to it here. Does it work?