Alexandre Courbot
2025-May-21 06:44 UTC
[PATCH v4 01/20] rust: dma: expose the count and size of CoherentAllocation
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>()
+ }
+
/// Returns the base address to the allocated region in the CPU's
virtual address space.
pub fn start_ptr(&self) -> *const T {
self.cpu_addr
--
2.49.0
Danilo Krummrich
2025-May-21 08:00 UTC
[PATCH v4 01/20] rust: dma: expose the count and size of CoherentAllocation
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()`.I think this also needs an invariant comment whenever self.count is set.> 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>() > + } > + > /// Returns the base address to the allocated region in the CPU's virtual address space. > pub fn start_ptr(&self) -> *const T { > self.cpu_addr > > -- > 2.49.0 >
Boqun Feng
2025-May-21 13:06 UTC
[PATCH v4 01/20] rust: dma: expose the count and size of CoherentAllocation
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. Regards, Boqun> + } > + > /// Returns the base address to the allocated region in the CPU's virtual address space. > pub fn start_ptr(&self) -> *const T { > self.cpu_addr > > -- > 2.49.0 >
Joel Fernandes
2025-May-21 15:57 UTC
[PATCH v4 01/20] rust: dma: expose the count and size of CoherentAllocation
On 5/21/2025 8:43 AM, 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. >If there is a coding error (say large count passed to alloc_coherent()), then I don't think it can guaranteed. Maybe use self.count.checked_mul(core::mem::size_of::<T>())? thanks, - Joel
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?