4 files changed, 197 insertions, 3 deletions

diff --git a/rust/qemu-api/src/lib.rs b/rust/qemu-api/src/lib.rs
index 3cf9371..e4316b2 100644
--- a/rust/qemu-api/src/lib.rs
+++ b/rust/qemu-api/src/lib.rs
@@ -19,6 +19,7 @@ pub mod c_str;
 pub mod callbacks;
 pub mod cell;
 pub mod irq;
+pub mod memory;
 pub mod module;
 pub mod offset_of;
 pub mod qdev;
diff --git a/rust/qemu-api/src/memory.rs b/rust/qemu-api/src/memory.rs
new file mode 100644
index 0000000..963d689
--- /dev/null
+++ b/rust/qemu-api/src/memory.rs
@@ -0,0 +1,191 @@
+// Copyright 2024 Red Hat, Inc.
+// Author(s): Paolo Bonzini <pbonzini@redhat.com>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+//! Bindings for `MemoryRegion` and `MemoryRegionOps`
+
+use std::{
+    ffi::{CStr, CString},
+    marker::{PhantomData, PhantomPinned},
+    os::raw::{c_uint, c_void},
+    ptr::addr_of,
+};
+
+pub use bindings::hwaddr;
+
+use crate::{
+    bindings::{self, device_endian, memory_region_init_io},
+    callbacks::FnCall,
+    prelude::*,
+    zeroable::Zeroable,
+};
+
+pub struct MemoryRegionOps<T>(
+    bindings::MemoryRegionOps,
+    // Note: quite often you'll see PhantomData<fn(&T)> mentioned when discussing
+    // covariance and contravariance; you don't need any of those to understand
+    // this usage of PhantomData.  Quite simply, MemoryRegionOps<T> *logically*
+    // holds callbacks that take an argument of type &T, except the type is erased
+    // before the callback is stored in the bindings::MemoryRegionOps field.
+    // The argument of PhantomData is a function pointer in order to represent
+    // that relationship; while that will also provide desirable and safe variance
+    // for T, variance is not the point but just a consequence.
+    PhantomData<fn(&T)>,
+);
+
+// SAFETY: When a *const T is passed to the callbacks, the call itself
+// is done in a thread-safe manner.  The invocation is okay as long as
+// T itself is `Sync`.
+unsafe impl<T: Sync> Sync for MemoryRegionOps<T> {}
+
+#[derive(Clone)]
+pub struct MemoryRegionOpsBuilder<T>(bindings::MemoryRegionOps, PhantomData<fn(&T)>);
+
+unsafe extern "C" fn memory_region_ops_read_cb<T, F: for<'a> FnCall<(&'a T, hwaddr, u32), u64>>(
+    opaque: *mut c_void,
+    addr: hwaddr,
+    size: c_uint,
+) -> u64 {
+    F::call((unsafe { &*(opaque.cast::<T>()) }, addr, size))
+}
+
+unsafe extern "C" fn memory_region_ops_write_cb<T, F: for<'a> FnCall<(&'a T, hwaddr, u64, u32)>>(
+    opaque: *mut c_void,
+    addr: hwaddr,
+    data: u64,
+    size: c_uint,
+) {
+    F::call((unsafe { &*(opaque.cast::<T>()) }, addr, data, size))
+}
+
+impl<T> MemoryRegionOpsBuilder<T> {
+    #[must_use]
+    pub const fn read<F: for<'a> FnCall<(&'a T, hwaddr, u32), u64>>(mut self, _f: &F) -> Self {
+        self.0.read = Some(memory_region_ops_read_cb::<T, F>);
+        self
+    }
+
+    #[must_use]
+    pub const fn write<F: for<'a> FnCall<(&'a T, hwaddr, u64, u32)>>(mut self, _f: &F) -> Self {
+        self.0.write = Some(memory_region_ops_write_cb::<T, F>);
+        self
+    }
+
+    #[must_use]
+    pub const fn big_endian(mut self) -> Self {
+        self.0.endianness = device_endian::DEVICE_BIG_ENDIAN;
+        self
+    }
+
+    #[must_use]
+    pub const fn little_endian(mut self) -> Self {
+        self.0.endianness = device_endian::DEVICE_LITTLE_ENDIAN;
+        self
+    }
+
+    #[must_use]
+    pub const fn native_endian(mut self) -> Self {
+        self.0.endianness = device_endian::DEVICE_NATIVE_ENDIAN;
+        self
+    }
+
+    #[must_use]
+    pub const fn valid_sizes(mut self, min: u32, max: u32) -> Self {
+        self.0.valid.min_access_size = min;
+        self.0.valid.max_access_size = max;
+        self
+    }
+
+    #[must_use]
+    pub const fn valid_unaligned(mut self) -> Self {
+        self.0.valid.unaligned = true;
+        self
+    }
+
+    #[must_use]
+    pub const fn impl_sizes(mut self, min: u32, max: u32) -> Self {
+        self.0.impl_.min_access_size = min;
+        self.0.impl_.max_access_size = max;
+        self
+    }
+
+    #[must_use]
+    pub const fn impl_unaligned(mut self) -> Self {
+        self.0.impl_.unaligned = true;
+        self
+    }
+
+    #[must_use]
+    pub const fn build(self) -> MemoryRegionOps<T> {
+        MemoryRegionOps::<T>(self.0, PhantomData)
+    }
+
+    #[must_use]
+    pub const fn new() -> Self {
+        Self(bindings::MemoryRegionOps::ZERO, PhantomData)
+    }
+}
+
+impl<T> Default for MemoryRegionOpsBuilder<T> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+/// A safe wrapper around [`bindings::MemoryRegion`].  Compared to the
+/// underlying C struct it is marked as pinned because the QOM tree
+/// contains a pointer to it.
+pub struct MemoryRegion {
+    inner: bindings::MemoryRegion,
+    _pin: PhantomPinned,
+}
+
+impl MemoryRegion {
+    // inline to ensure that it is not included in tests, which only
+    // link to hwcore and qom.  FIXME: inlining is actually the opposite
+    // of what we want, since this is the type-erased version of the
+    // init_io function below.  Look into splitting the qemu_api crate.
+    #[inline(always)]
+    unsafe fn do_init_io(
+        slot: *mut bindings::MemoryRegion,
+        owner: *mut Object,
+        ops: &'static bindings::MemoryRegionOps,
+        name: &'static str,
+        size: u64,
+    ) {
+        unsafe {
+            let cstr = CString::new(name).unwrap();
+            memory_region_init_io(
+                slot,
+                owner.cast::<Object>(),
+                ops,
+                owner.cast::<c_void>(),
+                cstr.as_ptr(),
+                size,
+            );
+        }
+    }
+
+    pub fn init_io<T: IsA<Object>>(
+        &mut self,
+        owner: *mut T,
+        ops: &'static MemoryRegionOps<T>,
+        name: &'static str,
+        size: u64,
+    ) {
+        unsafe {
+            Self::do_init_io(&mut self.inner, owner.cast::<Object>(), &ops.0, name, size);
+        }
+    }
+
+    pub(crate) const fn as_mut_ptr(&self) -> *mut bindings::MemoryRegion {
+        addr_of!(self.inner) as *mut _
+    }
+}
+
+unsafe impl ObjectType for MemoryRegion {
+    type Class = bindings::MemoryRegionClass;
+    const TYPE_NAME: &'static CStr =
+        unsafe { CStr::from_bytes_with_nul_unchecked(bindings::TYPE_MEMORY_REGION) };
+}
+qom_isa!(MemoryRegion: Object);
diff --git a/rust/qemu-api/src/sysbus.rs b/rust/qemu-api/src/sysbus.rs
index e6762b5..c27dbf7 100644
--- a/rust/qemu-api/src/sysbus.rs
+++ b/rust/qemu-api/src/sysbus.rs
@@ -2,7 +2,7 @@
 // Author(s): Paolo Bonzini <pbonzini@redhat.com>
 // SPDX-License-Identifier: GPL-2.0-or-later
 
-use std::{ffi::CStr, ptr::addr_of};
+use std::ffi::CStr;
 
 pub use bindings::{SysBusDevice, SysBusDeviceClass};
 
@@ -10,6 +10,7 @@ use crate::{
     bindings,
     cell::bql_locked,
     irq::InterruptSource,
+    memory::MemoryRegion,
     prelude::*,
     qdev::{DeviceClass, DeviceState},
     qom::ClassInitImpl,
@@ -42,10 +43,10 @@ where
     /// important, since whoever creates the sysbus device will refer to the
     /// region with a number that corresponds to the order of calls to
     /// `init_mmio`.
-    fn init_mmio(&self, iomem: &bindings::MemoryRegion) {
+    fn init_mmio(&self, iomem: &MemoryRegion) {
         assert!(bql_locked());
         unsafe {
-            bindings::sysbus_init_mmio(self.as_mut_ptr(), addr_of!(*iomem) as *mut _);
+            bindings::sysbus_init_mmio(self.as_mut_ptr(), iomem.as_mut_ptr());
         }
     }
 
diff --git a/rust/qemu-api/src/zeroable.rs b/rust/qemu-api/src/zeroable.rs
index 7b04947..75742b5 100644
--- a/rust/qemu-api/src/zeroable.rs
+++ b/rust/qemu-api/src/zeroable.rs
@@ -100,3 +100,4 @@ impl_zeroable!(crate::bindings::VMStateField);
 impl_zeroable!(crate::bindings::VMStateDescription);
 impl_zeroable!(crate::bindings::MemoryRegionOps__bindgen_ty_1);
 impl_zeroable!(crate::bindings::MemoryRegionOps__bindgen_ty_2);
+impl_zeroable!(crate::bindings::MemoryRegionOps);