Merge tag 'for-upstream' of https://gitlab.com/bonzini/qemu into staging

* qom: Use command line syntax for default values in help
* i386: support cache topology with machine's configuration
* rust: fix duplicate symbols from monitor-fd.c
* rust: add module to convert between success/-errno and io::Result
* rust: move class_init implementation from trait to method
* pvg: configuration improvements
* kvm guestmemfd: replace assertion with error
* riscv: cleanups
* target/i386/hvf: cleanups to emulation
* target/i386: add Zhaoxin and Yongfeng CPU model

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# gpg: Signature made Wed 26 Feb 2025 16:56:43 HKT
# gpg:                using RSA key F13338574B662389866C7682BFFBD25F78C7AE83
# gpg:                issuer "pbonzini@redhat.com"
# gpg: Good signature from "Paolo Bonzini <bonzini@gnu.org>" [full]
# gpg:                 aka "Paolo Bonzini <pbonzini@redhat.com>" [full]
# Primary key fingerprint: 46F5 9FBD 57D6 12E7 BFD4  E2F7 7E15 100C CD36 69B1
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* tag 'for-upstream' of https://gitlab.com/bonzini/qemu: (34 commits)
  target/i386: Mask CMPLegacy bit in CPUID[0x80000001].ECX for Zhaoxin CPUs
  target/i386: Introduce Zhaoxin Yongfeng CPU model
  target/i386: Add CPUID leaf 0xC000_0001 EDX definitions
  target/i386: Add support for Zhaoxin CPU vendor identification
  target/riscv: move 128-bit check to TCG realize
  target/riscv: remove unused macro DEFINE_CPU
  i386/cpu: add has_caches flag to check smp_cache configuration
  i386/pc: Support cache topology in -machine for PC machine
  i386/cpu: Update cache topology with machine's configuration
  i386/cpu: Support module level cache topology
  rust: qom: get rid of ClassInitImpl
  rust: pl011, qemu_api tests: do not use ClassInitImpl
  rust: qom: add ObjectImpl::CLASS_INIT
  rust: add SysBusDeviceImpl
  rust: add IsA bounds to QOM implementation traits
  target/i386/hvf: drop some dead code
  target/i386/hvf: move and rename simulate_{rdmsr, wrmsr}
  target/i386/hvf: move and rename {load, store}_regs
  target/i386/hvf: use x86_segment in x86_decode.c
  target/i386/hvf: fix the declaration of hvf_handle_io
  ...

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

11 files changed, 502 insertions, 144 deletions

diff --git a/rust/qemu-api/Cargo.toml b/rust/qemu-api/Cargo.toml
index a51dd14..57747bc 100644
--- a/rust/qemu-api/Cargo.toml
+++ b/rust/qemu-api/Cargo.toml
@@ -16,6 +16,7 @@ rust-version = "1.63.0"
 
 [dependencies]
 qemu_api_macros = { path = "../qemu-api-macros" }
+libc = "0.2.162"
 
 [build-dependencies]
 version_check = "~0.9"
diff --git a/rust/qemu-api/meson.build b/rust/qemu-api/meson.build
index 2e9c107..bcf1cf7 100644
--- a/rust/qemu-api/meson.build
+++ b/rust/qemu-api/meson.build
@@ -2,6 +2,8 @@ _qemu_api_cfg = run_command(rustc_args,
   '--config-headers', config_host_h, '--features', files('Cargo.toml'),
   capture: true, check: true).stdout().strip().splitlines()
 
+libc_dep = dependency('libc-0.2-rs')
+
 # _qemu_api_cfg += ['--cfg', 'feature="allocator"']
 if rustc.version().version_compare('>=1.77.0')
   _qemu_api_cfg += ['--cfg', 'has_offset_of']
@@ -22,6 +24,7 @@ _qemu_api_rs = static_library(
       'src/cell.rs',
       'src/chardev.rs',
       'src/c_str.rs',
+      'src/errno.rs',
       'src/irq.rs',
       'src/memory.rs',
       'src/module.rs',
@@ -39,6 +42,7 @@ _qemu_api_rs = static_library(
   override_options: ['rust_std=2021', 'build.rust_std=2021'],
   rust_abi: 'rust',
   rust_args: _qemu_api_cfg,
+  dependencies: libc_dep,
 )
 
 rust.test('rust-qemu-api-tests', _qemu_api_rs,
diff --git a/rust/qemu-api/src/assertions.rs b/rust/qemu-api/src/assertions.rs
index fa1a18d..104dec3 100644
--- a/rust/qemu-api/src/assertions.rs
+++ b/rust/qemu-api/src/assertions.rs
@@ -92,3 +92,31 @@ macro_rules! assert_field_type {
         };
     };
 }
+
+/// Assert that an expression matches a pattern.  This can also be
+/// useful to compare enums that do not implement `Eq`.
+///
+/// # Examples
+///
+/// ```
+/// # use qemu_api::assert_match;
+/// // JoinHandle does not implement `Eq`, therefore the result
+/// // does not either.
+/// let result: Result<std::thread::JoinHandle<()>, u32> = Err(42);
+/// assert_match!(result, Err(42));
+/// ```
+#[macro_export]
+macro_rules! assert_match {
+    ($a:expr, $b:pat) => {
+        assert!(
+            match $a {
+                $b => true,
+                _ => false,
+            },
+            "{} = {:?} does not match {}",
+            stringify!($a),
+            $a,
+            stringify!($b)
+        );
+    };
+}
diff --git a/rust/qemu-api/src/errno.rs b/rust/qemu-api/src/errno.rs
new file mode 100644
index 0000000..18d1014
--- /dev/null
+++ b/rust/qemu-api/src/errno.rs
@@ -0,0 +1,345 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+//! Utility functions to convert `errno` to and from
+//! [`io::Error`]/[`io::Result`]
+//!
+//! QEMU C functions often have a "positive success/negative `errno`" calling
+//! convention.  This module provides functions to portably convert an integer
+//! into an [`io::Result`] and back.
+
+use std::{convert::TryFrom, io, io::ErrorKind};
+
+/// An `errno` value that can be converted into an [`io::Error`]
+pub struct Errno(pub u16);
+
+// On Unix, from_raw_os_error takes an errno value and OS errors
+// are printed using strerror.  On Windows however it takes a
+// GetLastError() value; therefore we need to convert errno values
+// into io::Error by hand.  This is the same mapping that the
+// standard library uses to retrieve the kind of OS errors
+// (`std::sys::pal::unix::decode_error_kind`).
+impl From<Errno> for ErrorKind {
+    fn from(value: Errno) -> ErrorKind {
+        use ErrorKind::*;
+        let Errno(errno) = value;
+        match i32::from(errno) {
+            libc::EPERM | libc::EACCES => PermissionDenied,
+            libc::ENOENT => NotFound,
+            libc::EINTR => Interrupted,
+            x if x == libc::EAGAIN || x == libc::EWOULDBLOCK => WouldBlock,
+            libc::ENOMEM => OutOfMemory,
+            libc::EEXIST => AlreadyExists,
+            libc::EINVAL => InvalidInput,
+            libc::EPIPE => BrokenPipe,
+            libc::EADDRINUSE => AddrInUse,
+            libc::EADDRNOTAVAIL => AddrNotAvailable,
+            libc::ECONNABORTED => ConnectionAborted,
+            libc::ECONNREFUSED => ConnectionRefused,
+            libc::ECONNRESET => ConnectionReset,
+            libc::ENOTCONN => NotConnected,
+            libc::ENOTSUP => Unsupported,
+            libc::ETIMEDOUT => TimedOut,
+            _ => Other,
+        }
+    }
+}
+
+// This is used on Windows for all io::Errors, but also on Unix if the
+// io::Error does not have a raw OS error.  This is the reversed
+// mapping of the above; EIO is returned for unknown ErrorKinds.
+impl From<io::ErrorKind> for Errno {
+    fn from(value: io::ErrorKind) -> Errno {
+        use ErrorKind::*;
+        let errno = match value {
+            // can be both EPERM or EACCES :( pick one
+            PermissionDenied => libc::EPERM,
+            NotFound => libc::ENOENT,
+            Interrupted => libc::EINTR,
+            WouldBlock => libc::EAGAIN,
+            OutOfMemory => libc::ENOMEM,
+            AlreadyExists => libc::EEXIST,
+            InvalidInput => libc::EINVAL,
+            BrokenPipe => libc::EPIPE,
+            AddrInUse => libc::EADDRINUSE,
+            AddrNotAvailable => libc::EADDRNOTAVAIL,
+            ConnectionAborted => libc::ECONNABORTED,
+            ConnectionRefused => libc::ECONNREFUSED,
+            ConnectionReset => libc::ECONNRESET,
+            NotConnected => libc::ENOTCONN,
+            Unsupported => libc::ENOTSUP,
+            TimedOut => libc::ETIMEDOUT,
+            _ => libc::EIO,
+        };
+        Errno(errno as u16)
+    }
+}
+
+impl From<Errno> for io::Error {
+    #[cfg(unix)]
+    fn from(value: Errno) -> io::Error {
+        let Errno(errno) = value;
+        io::Error::from_raw_os_error(errno.into())
+    }
+
+    #[cfg(windows)]
+    fn from(value: Errno) -> io::Error {
+        let error_kind: ErrorKind = value.into();
+        error_kind.into()
+    }
+}
+
+impl From<io::Error> for Errno {
+    fn from(value: io::Error) -> Errno {
+        if cfg!(unix) {
+            if let Some(errno) = value.raw_os_error() {
+                return Errno(u16::try_from(errno).unwrap());
+            }
+        }
+        value.kind().into()
+    }
+}
+
+/// Internal traits; used to enable [`into_io_result`] and [`into_neg_errno`]
+/// for the "right" set of types.
+mod traits {
+    use super::Errno;
+
+    /// A signed type that can be converted into an
+    /// [`io::Result`](std::io::Result)
+    pub trait GetErrno {
+        /// Unsigned variant of `Self`, used as the type for the `Ok` case.
+        type Out;
+
+        /// Return `Ok(self)` if positive, `Err(Errno(-self))` if negative
+        fn into_errno_result(self) -> Result<Self::Out, Errno>;
+    }
+
+    /// A type that can be taken out of an [`io::Result`](std::io::Result) and
+    /// converted into "positive success/negative `errno`" convention.
+    pub trait MergeErrno {
+        /// Signed variant of `Self`, used as the return type of
+        /// [`into_neg_errno`](super::into_neg_errno).
+        type Out: From<u16> + std::ops::Neg<Output = Self::Out>;
+
+        /// Return `self`, asserting that it is in range
+        fn map_ok(self) -> Self::Out;
+    }
+
+    macro_rules! get_errno {
+        ($t:ty, $out:ty) => {
+            impl GetErrno for $t {
+                type Out = $out;
+                fn into_errno_result(self) -> Result<Self::Out, Errno> {
+                    match self {
+                        0.. => Ok(self as $out),
+                        -65535..=-1 => Err(Errno(-self as u16)),
+                        _ => panic!("{self} is not a negative errno"),
+                    }
+                }
+            }
+        };
+    }
+
+    get_errno!(i32, u32);
+    get_errno!(i64, u64);
+    get_errno!(isize, usize);
+
+    macro_rules! merge_errno {
+        ($t:ty, $out:ty) => {
+            impl MergeErrno for $t {
+                type Out = $out;
+                fn map_ok(self) -> Self::Out {
+                    self.try_into().unwrap()
+                }
+            }
+        };
+    }
+
+    merge_errno!(u8, i32);
+    merge_errno!(u16, i32);
+    merge_errno!(u32, i32);
+    merge_errno!(u64, i64);
+
+    impl MergeErrno for () {
+        type Out = i32;
+        fn map_ok(self) -> i32 {
+            0
+        }
+    }
+}
+
+use traits::{GetErrno, MergeErrno};
+
+/// Convert an integer value into a [`io::Result`].
+///
+/// Positive values are turned into an `Ok` result; negative values
+/// are interpreted as negated `errno` and turned into an `Err`.
+///
+/// ```
+/// # use qemu_api::errno::into_io_result;
+/// # use std::io::ErrorKind;
+/// let ok = into_io_result(1i32).unwrap();
+/// assert_eq!(ok, 1u32);
+///
+/// let err = into_io_result(-1i32).unwrap_err(); // -EPERM
+/// assert_eq!(err.kind(), ErrorKind::PermissionDenied);
+/// ```
+///
+/// # Panics
+///
+/// Since the result is an unsigned integer, negative values must
+/// be close to 0; values that are too far away are considered
+/// likely overflows and will panic:
+///
+/// ```should_panic
+/// # use qemu_api::errno::into_io_result;
+/// # #[allow(dead_code)]
+/// let err = into_io_result(-0x1234_5678i32); // panic
+/// ```
+pub fn into_io_result<T: GetErrno>(value: T) -> io::Result<T::Out> {
+    value.into_errno_result().map_err(Into::into)
+}
+
+/// Convert a [`Result`] into an integer value, using negative `errno`
+/// values to report errors.
+///
+/// ```
+/// # use qemu_api::errno::into_neg_errno;
+/// # use std::io::{self, ErrorKind};
+/// let ok: io::Result<()> = Ok(());
+/// assert_eq!(into_neg_errno(ok), 0);
+///
+/// let err: io::Result<()> = Err(ErrorKind::InvalidInput.into());
+/// assert_eq!(into_neg_errno(err), -22); // -EINVAL
+/// ```
+///
+/// Since this module also provides the ability to convert [`io::Error`]
+/// to an `errno` value, [`io::Result`] is the most commonly used type
+/// for the argument of this function:
+///
+/// # Panics
+///
+/// Since the result is a signed integer, integer `Ok` values must remain
+/// positive:
+///
+/// ```should_panic
+/// # use qemu_api::errno::into_neg_errno;
+/// # use std::io;
+/// let err: io::Result<u32> = Ok(0x8899_AABB);
+/// into_neg_errno(err) // panic
+/// # ;
+/// ```
+pub fn into_neg_errno<T: MergeErrno, E: Into<Errno>>(value: Result<T, E>) -> T::Out {
+    match value {
+        Ok(x) => x.map_ok(),
+        Err(err) => -T::Out::from(err.into().0),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::io::ErrorKind;
+
+    use super::*;
+    use crate::assert_match;
+
+    #[test]
+    pub fn test_from_u8() {
+        let ok: io::Result<_> = Ok(42u8);
+        assert_eq!(into_neg_errno(ok), 42);
+
+        let err: io::Result<u8> = Err(io::ErrorKind::PermissionDenied.into());
+        assert_eq!(into_neg_errno(err), -1);
+
+        if cfg!(unix) {
+            let os_err: io::Result<u8> = Err(io::Error::from_raw_os_error(10));
+            assert_eq!(into_neg_errno(os_err), -10);
+        }
+    }
+
+    #[test]
+    pub fn test_from_u16() {
+        let ok: io::Result<_> = Ok(1234u16);
+        assert_eq!(into_neg_errno(ok), 1234);
+
+        let err: io::Result<u16> = Err(io::ErrorKind::PermissionDenied.into());
+        assert_eq!(into_neg_errno(err), -1);
+
+        if cfg!(unix) {
+            let os_err: io::Result<u16> = Err(io::Error::from_raw_os_error(10));
+            assert_eq!(into_neg_errno(os_err), -10);
+        }
+    }
+
+    #[test]
+    pub fn test_i32() {
+        assert_match!(into_io_result(1234i32), Ok(1234));
+
+        let err = into_io_result(-1i32).unwrap_err();
+        #[cfg(unix)]
+        assert_match!(err.raw_os_error(), Some(1));
+        assert_match!(err.kind(), ErrorKind::PermissionDenied);
+    }
+
+    #[test]
+    pub fn test_from_u32() {
+        let ok: io::Result<_> = Ok(1234u32);
+        assert_eq!(into_neg_errno(ok), 1234);
+
+        let err: io::Result<u32> = Err(io::ErrorKind::PermissionDenied.into());
+        assert_eq!(into_neg_errno(err), -1);
+
+        if cfg!(unix) {
+            let os_err: io::Result<u32> = Err(io::Error::from_raw_os_error(10));
+            assert_eq!(into_neg_errno(os_err), -10);
+        }
+    }
+
+    #[test]
+    pub fn test_i64() {
+        assert_match!(into_io_result(1234i64), Ok(1234));
+
+        let err = into_io_result(-22i64).unwrap_err();
+        #[cfg(unix)]
+        assert_match!(err.raw_os_error(), Some(22));
+        assert_match!(err.kind(), ErrorKind::InvalidInput);
+    }
+
+    #[test]
+    pub fn test_from_u64() {
+        let ok: io::Result<_> = Ok(1234u64);
+        assert_eq!(into_neg_errno(ok), 1234);
+
+        let err: io::Result<u64> = Err(io::ErrorKind::InvalidInput.into());
+        assert_eq!(into_neg_errno(err), -22);
+
+        if cfg!(unix) {
+            let os_err: io::Result<u64> = Err(io::Error::from_raw_os_error(6));
+            assert_eq!(into_neg_errno(os_err), -6);
+        }
+    }
+
+    #[test]
+    pub fn test_isize() {
+        assert_match!(into_io_result(1234isize), Ok(1234));
+
+        let err = into_io_result(-4isize).unwrap_err();
+        #[cfg(unix)]
+        assert_match!(err.raw_os_error(), Some(4));
+        assert_match!(err.kind(), ErrorKind::Interrupted);
+    }
+
+    #[test]
+    pub fn test_from_unit() {
+        let ok: io::Result<_> = Ok(());
+        assert_eq!(into_neg_errno(ok), 0);
+
+        let err: io::Result<()> = Err(io::ErrorKind::OutOfMemory.into());
+        assert_eq!(into_neg_errno(err), -12);
+
+        if cfg!(unix) {
+            let os_err: io::Result<()> = Err(io::Error::from_raw_os_error(2));
+            assert_eq!(into_neg_errno(os_err), -2);
+        }
+    }
+}
diff --git a/rust/qemu-api/src/irq.rs b/rust/qemu-api/src/irq.rs
index d1c9dc9..34c1926 100644
--- a/rust/qemu-api/src/irq.rs
+++ b/rust/qemu-api/src/irq.rs
@@ -4,8 +4,7 @@
 
 //! Bindings for interrupt sources
 
-use core::ptr;
-use std::{ffi::CStr, marker::PhantomData, os::raw::c_int};
+use std::{ffi::CStr, marker::PhantomData, os::raw::c_int, ptr};
 
 use crate::{
     bindings::{self, qemu_set_irq},
diff --git a/rust/qemu-api/src/lib.rs b/rust/qemu-api/src/lib.rs
index ed1a8f9..05f38b5 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 chardev;
+pub mod errno;
 pub mod irq;
 pub mod memory;
 pub mod module;
diff --git a/rust/qemu-api/src/prelude.rs b/rust/qemu-api/src/prelude.rs
index fbf0ee2..634acf3 100644
--- a/rust/qemu-api/src/prelude.rs
+++ b/rust/qemu-api/src/prelude.rs
@@ -9,6 +9,8 @@ pub use crate::bitops::IntegerExt;
 pub use crate::cell::BqlCell;
 pub use crate::cell::BqlRefCell;
 
+pub use crate::errno;
+
 pub use crate::qdev::DeviceMethods;
 
 pub use crate::qom::InterfaceType;
diff --git a/rust/qemu-api/src/qdev.rs b/rust/qemu-api/src/qdev.rs
index 3a7aa4d..c136457 100644
--- a/rust/qemu-api/src/qdev.rs
+++ b/rust/qemu-api/src/qdev.rs
@@ -19,7 +19,7 @@ use crate::{
     chardev::Chardev,
     irq::InterruptSource,
     prelude::*,
-    qom::{ClassInitImpl, ObjectClass, ObjectImpl, Owned},
+    qom::{ObjectClass, ObjectImpl, Owned},
     vmstate::VMStateDescription,
 };
 
@@ -86,7 +86,7 @@ unsafe extern "C" fn rust_resettable_exit_fn<T: ResettablePhasesImpl>(
 }
 
 /// Trait providing the contents of [`DeviceClass`].
-pub trait DeviceImpl: ObjectImpl + ResettablePhasesImpl {
+pub trait DeviceImpl: ObjectImpl + ResettablePhasesImpl + IsA<DeviceState> {
     /// _Realization_ is the second stage of device creation. It contains
     /// all operations that depend on device properties and can fail (note:
     /// this is not yet supported for Rust devices).
@@ -113,7 +113,7 @@ pub trait DeviceImpl: ObjectImpl + ResettablePhasesImpl {
 /// # Safety
 ///
 /// This function is only called through the QOM machinery and
-/// used by the `ClassInitImpl<DeviceClass>` trait.
+/// used by `DeviceClass::class_init`.
 /// We expect the FFI user of this function to pass a valid pointer that
 /// can be downcasted to type `T`. We also expect the device is
 /// readable/writeable from one thread at any time.
@@ -127,43 +127,41 @@ unsafe impl InterfaceType for ResettableClass {
         unsafe { CStr::from_bytes_with_nul_unchecked(bindings::TYPE_RESETTABLE_INTERFACE) };
 }
 
-impl<T> ClassInitImpl<ResettableClass> for T
-where
-    T: ResettablePhasesImpl,
-{
-    fn class_init(rc: &mut ResettableClass) {
+impl ResettableClass {
+    /// Fill in the virtual methods of `ResettableClass` based on the
+    /// definitions in the `ResettablePhasesImpl` trait.
+    pub fn class_init<T: ResettablePhasesImpl>(&mut self) {
         if <T as ResettablePhasesImpl>::ENTER.is_some() {
-            rc.phases.enter = Some(rust_resettable_enter_fn::<T>);
+            self.phases.enter = Some(rust_resettable_enter_fn::<T>);
         }
         if <T as ResettablePhasesImpl>::HOLD.is_some() {
-            rc.phases.hold = Some(rust_resettable_hold_fn::<T>);
+            self.phases.hold = Some(rust_resettable_hold_fn::<T>);
         }
         if <T as ResettablePhasesImpl>::EXIT.is_some() {
-            rc.phases.exit = Some(rust_resettable_exit_fn::<T>);
+            self.phases.exit = Some(rust_resettable_exit_fn::<T>);
         }
     }
 }
 
-impl<T> ClassInitImpl<DeviceClass> for T
-where
-    T: ClassInitImpl<ObjectClass> + ClassInitImpl<ResettableClass> + DeviceImpl,
-{
-    fn class_init(dc: &mut DeviceClass) {
+impl DeviceClass {
+    /// Fill in the virtual methods of `DeviceClass` based on the definitions in
+    /// the `DeviceImpl` trait.
+    pub fn class_init<T: DeviceImpl>(&mut self) {
         if <T as DeviceImpl>::REALIZE.is_some() {
-            dc.realize = Some(rust_realize_fn::<T>);
+            self.realize = Some(rust_realize_fn::<T>);
         }
         if let Some(vmsd) = <T as DeviceImpl>::vmsd() {
-            dc.vmsd = vmsd;
+            self.vmsd = vmsd;
         }
         let prop = <T as DeviceImpl>::properties();
         if !prop.is_empty() {
             unsafe {
-                bindings::device_class_set_props_n(dc, prop.as_ptr(), prop.len());
+                bindings::device_class_set_props_n(self, prop.as_ptr(), prop.len());
             }
         }
 
-        ResettableClass::interface_init::<T, DeviceState>(dc);
-        <T as ClassInitImpl<ObjectClass>>::class_init(&mut dc.parent_class);
+        ResettableClass::cast::<DeviceState>(self).class_init::<T>();
+        self.parent_class.class_init::<T>();
     }
 }
 
diff --git a/rust/qemu-api/src/qom.rs b/rust/qemu-api/src/qom.rs
index 3d5ab2d..5488643 100644
--- a/rust/qemu-api/src/qom.rs
+++ b/rust/qemu-api/src/qom.rs
@@ -37,11 +37,8 @@
 //! * a trait for virtual method implementations, for example `DeviceImpl`.
 //!   Child classes implement this trait to provide their own behavior for
 //!   virtual methods. The trait's methods take `&self` to access instance data.
-//!
-//! * an implementation of [`ClassInitImpl`], for example
-//!   `ClassInitImpl<DeviceClass>`. This fills the vtable in the class struct;
-//!   the source for this is the `*Impl` trait; the associated consts and
-//!   functions if needed are wrapped to map C types into Rust types.
+//!   The traits have the appropriate specialization of `IsA<>` as a supertrait,
+//!   for example `IsA<DeviceState>` for `DeviceImpl`.
 //!
 //! * a trait for instance methods, for example `DeviceMethods`. This trait is
 //!   automatically implemented for any reference or smart pointer to a device
@@ -52,6 +49,48 @@
 //!   This provides access to class-wide functionality that doesn't depend on
 //!   instance data. Like instance methods, these are automatically inherited by
 //!   child classes.
+//!
+//! # Class structures
+//!
+//! Each QOM class that has virtual methods describes them in a
+//! _class struct_.  Class structs include a parent field corresponding
+//! to the vtable of the parent class, all the way up to [`ObjectClass`].
+//!
+//! As mentioned above, virtual methods are defined via traits such as
+//! `DeviceImpl`.  Class structs do not define any trait but, conventionally,
+//! all of them have a `class_init` method to initialize the virtual methods
+//! based on the trait and then call the same method on the superclass.
+//!
+//! ```ignore
+//! impl YourSubclassClass
+//! {
+//!     pub fn class_init<T: YourSubclassImpl>(&mut self) {
+//!         ...
+//!         klass.parent_class::class_init<T>();
+//!     }
+//! }
+//! ```
+//!
+//! If a class implements a QOM interface.  In that case, the function must
+//! contain, for each interface, an extra forwarding call as follows:
+//!
+//! ```ignore
+//! ResettableClass::cast::<Self>(self).class_init::<Self>();
+//! ```
+//!
+//! These `class_init` functions are methods on the class rather than a trait,
+//! because the bound on `T` (`DeviceImpl` in this case), will change for every
+//! class struct.  The functions are pointed to by the
+//! [`ObjectImpl::CLASS_INIT`] function pointer. While there is no default
+//! implementation, in most cases it will be enough to write it as follows:
+//!
+//! ```ignore
+//! const CLASS_INIT: fn(&mut Self::Class)> = Self::Class::class_init::<Self>;
+//! ```
+//!
+//! This design incurs a small amount of code duplication but, by not using
+//! traits, it allows the flexibility of implementing bindings in any crate,
+//! without incurring into violations of orphan rules for traits.
 
 use std::{
     ffi::CStr,
@@ -178,7 +217,7 @@ unsafe extern "C" fn rust_instance_post_init<T: ObjectImpl>(obj: *mut Object) {
     T::INSTANCE_POST_INIT.unwrap()(unsafe { state.as_ref() });
 }
 
-unsafe extern "C" fn rust_class_init<T: ObjectType + ClassInitImpl<T::Class>>(
+unsafe extern "C" fn rust_class_init<T: ObjectType + ObjectImpl>(
     klass: *mut ObjectClass,
     _data: *mut c_void,
 ) {
@@ -188,7 +227,7 @@ unsafe extern "C" fn rust_class_init<T: ObjectType + ClassInitImpl<T::Class>>(
     // SAFETY: klass is a T::Class, since rust_class_init<T>
     // is called from QOM core as the class_init function
     // for class T
-    T::class_init(unsafe { klass.as_mut() })
+    <T as ObjectImpl>::CLASS_INIT(unsafe { klass.as_mut() })
 }
 
 unsafe extern "C" fn drop_object<T: ObjectImpl>(obj: *mut Object) {
@@ -277,19 +316,25 @@ pub unsafe trait InterfaceType: Sized {
     /// for this interface.
     const TYPE_NAME: &'static CStr;
 
-    /// Initialize the vtable for the interface; the generic argument `T` is the
-    /// type being initialized, while the generic argument `U` is the type that
+    /// Return the vtable for the interface; `U` is the type that
     /// lists the interface in its `TypeInfo`.
     ///
+    /// # Examples
+    ///
+    /// This function is usually called by a `class_init` method in `U::Class`.
+    /// For example, `DeviceClass::class_init<T>` initializes its `Resettable`
+    /// interface as follows:
+    ///
+    /// ```ignore
+    /// ResettableClass::cast::<DeviceState>(self).class_init::<T>();
+    /// ```
+    ///
+    /// where `T` is the concrete subclass that is being initialized.
+    ///
     /// # Panics
     ///
     /// Panic if the incoming argument if `T` does not implement the interface.
-    fn interface_init<
-        T: ObjectType + ClassInitImpl<Self> + ClassInitImpl<U::Class>,
-        U: ObjectType,
-    >(
-        klass: &mut U::Class,
-    ) {
+    fn cast<U: ObjectType>(klass: &mut U::Class) -> &mut Self {
         unsafe {
             // SAFETY: upcasting to ObjectClass is always valid, and the
             // return type is either NULL or the argument itself
@@ -298,8 +343,7 @@ pub unsafe trait InterfaceType: Sized {
                 Self::TYPE_NAME.as_ptr(),
             )
             .cast();
-
-            <T as ClassInitImpl<Self>>::class_init(result.as_mut().unwrap())
+            result.as_mut().unwrap()
         }
     }
 }
@@ -497,7 +541,7 @@ impl<T: ObjectType> ObjectDeref for &mut T {}
 impl<T: ObjectType> ObjectCastMut for &mut T {}
 
 /// Trait a type must implement to be registered with QEMU.
-pub trait ObjectImpl: ObjectType + ClassInitImpl<Self::Class> {
+pub trait ObjectImpl: ObjectType + IsA<Object> {
     /// The parent of the type.  This should match the first field of the
     /// struct that implements `ObjectImpl`, minus the `ParentField<_>` wrapper.
     type ParentType: ObjectType;
@@ -550,85 +594,26 @@ pub trait ObjectImpl: ObjectType + ClassInitImpl<Self::Class> {
 
     // methods on ObjectClass
     const UNPARENT: Option<fn(&Self)> = None;
-}
 
-/// Internal trait used to automatically fill in a class struct.
-///
-/// Each QOM class that has virtual methods describes them in a
-/// _class struct_.  Class structs include a parent field corresponding
-/// to the vtable of the parent class, all the way up to [`ObjectClass`].
-/// Each QOM type has one such class struct; this trait takes care of
-/// initializing the `T` part of the class struct, for the type that
-/// implements the trait.
-///
-/// Each struct will implement this trait with `T` equal to each
-/// superclass.  For example, a device should implement at least
-/// `ClassInitImpl<`[`DeviceClass`](crate::qdev::DeviceClass)`>` and
-/// `ClassInitImpl<`[`ObjectClass`]`>`.  Such implementations are made
-/// in one of two ways.
-///
-/// For most superclasses, `ClassInitImpl` is provided by the `qemu-api`
-/// crate itself.  The Rust implementation of methods will come from a
-/// trait like [`ObjectImpl`] or [`DeviceImpl`](crate::qdev::DeviceImpl),
-/// and `ClassInitImpl` is provided by blanket implementations that
-/// operate on all implementors of the `*Impl`* trait.  For example:
-///
-/// ```ignore
-/// impl<T> ClassInitImpl<DeviceClass> for T
-/// where
-///     T: ClassInitImpl<ObjectClass> + DeviceImpl,
-/// ```
-///
-/// The bound on `ClassInitImpl<ObjectClass>` is needed so that,
-/// after initializing the `DeviceClass` part of the class struct,
-/// the parent [`ObjectClass`] is initialized as well.
-///
-/// The other case is when manual implementation of the trait is needed.
-/// This covers the following cases:
-///
-/// * if a class implements a QOM interface, the Rust code _has_ to define its
-///   own class struct `FooClass` and implement `ClassInitImpl<FooClass>`.
-///   `ClassInitImpl<FooClass>`'s `class_init` method will then forward to
-///   multiple other `class_init`s, for the interfaces as well as the
-///   superclass. (Note that there is no Rust example yet for using interfaces).
-///
-/// * for classes implemented outside the ``qemu-api`` crate, it's not possible
-///   to add blanket implementations like the above one, due to orphan rules. In
-///   that case, the easiest solution is to implement
-///   `ClassInitImpl<YourSuperclass>` for each subclass and not have a
-///   `YourSuperclassImpl` trait at all.
-///
-/// ```ignore
-/// impl ClassInitImpl<YourSuperclass> for YourSubclass {
-///     fn class_init(klass: &mut YourSuperclass) {
-///         klass.some_method = Some(Self::some_method);
-///         <Self as ClassInitImpl<SysBusDeviceClass>>::class_init(&mut klass.parent_class);
-///     }
-/// }
-/// ```
-///
-///   While this method incurs a small amount of code duplication,
-///   it is generally limited to the recursive call on the last line.
-///   This is because classes defined in Rust do not need the same
-///   glue code that is needed when the classes are defined in C code.
-///   You may consider using a macro if you have many subclasses.
-pub trait ClassInitImpl<T> {
-    /// Initialize `klass` to point to the virtual method implementations
+    /// Store into the argument the virtual method implementations
     /// for `Self`.  On entry, the virtual method pointers are set to
     /// the default values coming from the parent classes; the function
     /// can change them to override virtual methods of a parent class.
     ///
-    /// The virtual method implementations usually come from another
-    /// trait, for example [`DeviceImpl`](crate::qdev::DeviceImpl)
-    /// when `T` is [`DeviceClass`](crate::qdev::DeviceClass).
+    /// Usually defined simply as `Self::Class::class_init::<Self>`;
+    /// however a default implementation cannot be included here, because the
+    /// bounds that the `Self::Class::class_init` method places on `Self` are
+    /// not known in advance.
     ///
-    /// On entry, `klass`'s parent class is initialized, while the other fields
+    /// # Safety
+    ///
+    /// While `klass`'s parent class is initialized on entry, the other fields
     /// are all zero; it is therefore assumed that all fields in `T` can be
     /// zeroed, otherwise it would not be possible to provide the class as a
     /// `&mut T`.  TODO: add a bound of [`Zeroable`](crate::zeroable::Zeroable)
     /// to T; this is more easily done once Zeroable does not require a manual
     /// implementation (Rust 1.75.0).
-    fn class_init(klass: &mut T);
+    const CLASS_INIT: fn(&mut Self::Class);
 }
 
 /// # Safety
@@ -641,13 +626,12 @@ unsafe extern "C" fn rust_unparent_fn<T: ObjectImpl>(dev: *mut Object) {
     T::UNPARENT.unwrap()(unsafe { state.as_ref() });
 }
 
-impl<T> ClassInitImpl<ObjectClass> for T
-where
-    T: ObjectImpl,
-{
-    fn class_init(oc: &mut ObjectClass) {
+impl ObjectClass {
+    /// Fill in the virtual methods of `ObjectClass` based on the definitions in
+    /// the `ObjectImpl` trait.
+    pub fn class_init<T: ObjectImpl>(&mut self) {
         if <T as ObjectImpl>::UNPARENT.is_some() {
-            oc.unparent = Some(rust_unparent_fn::<T>);
+            self.unparent = Some(rust_unparent_fn::<T>);
         }
     }
 }
diff --git a/rust/qemu-api/src/sysbus.rs b/rust/qemu-api/src/sysbus.rs
index fa36e12..04821a2 100644
--- a/rust/qemu-api/src/sysbus.rs
+++ b/rust/qemu-api/src/sysbus.rs
@@ -14,8 +14,8 @@ use crate::{
     irq::{IRQState, InterruptSource},
     memory::MemoryRegion,
     prelude::*,
-    qdev::{DeviceClass, DeviceState},
-    qom::{ClassInitImpl, Owned},
+    qdev::{DeviceImpl, DeviceState},
+    qom::Owned,
 };
 
 unsafe impl ObjectType for SysBusDevice {
@@ -25,13 +25,14 @@ unsafe impl ObjectType for SysBusDevice {
 }
 qom_isa!(SysBusDevice: DeviceState, Object);
 
-// TODO: add SysBusDeviceImpl
-impl<T> ClassInitImpl<SysBusDeviceClass> for T
-where
-    T: ClassInitImpl<DeviceClass>,
-{
-    fn class_init(sdc: &mut SysBusDeviceClass) {
-        <T as ClassInitImpl<DeviceClass>>::class_init(&mut sdc.parent_class);
+// TODO: add virtual methods
+pub trait SysBusDeviceImpl: DeviceImpl + IsA<SysBusDevice> {}
+
+impl SysBusDeviceClass {
+    /// Fill in the virtual methods of `SysBusDeviceClass` based on the
+    /// definitions in the `SysBusDeviceImpl` trait.
+    pub fn class_init<T: SysBusDeviceImpl>(self: &mut SysBusDeviceClass) {
+        self.parent_class.class_init::<T>();
     }
 }
 
diff --git a/rust/qemu-api/tests/tests.rs b/rust/qemu-api/tests/tests.rs
index 92dbfb8..e398578 100644
--- a/rust/qemu-api/tests/tests.rs
+++ b/rust/qemu-api/tests/tests.rs
@@ -8,13 +8,14 @@ use std::{
 };
 
 use qemu_api::{
-    bindings::*,
+    bindings::{module_call_init, module_init_type, object_new, object_unref, qdev_prop_bool},
     c_str,
     cell::{self, BqlCell},
     declare_properties, define_property,
     prelude::*,
-    qdev::{DeviceClass, DeviceImpl, DeviceState, Property, ResettablePhasesImpl},
-    qom::{ClassInitImpl, ObjectImpl, ParentField},
+    qdev::{DeviceImpl, DeviceState, Property, ResettablePhasesImpl},
+    qom::{ObjectImpl, ParentField},
+    sysbus::SysBusDevice,
     vmstate::VMStateDescription,
     zeroable::Zeroable,
 };
@@ -40,6 +41,12 @@ pub struct DummyClass {
     parent_class: <DeviceState as ObjectType>::Class,
 }
 
+impl DummyClass {
+    pub fn class_init<T: DeviceImpl>(self: &mut DummyClass) {
+        self.parent_class.class_init::<T>();
+    }
+}
+
 declare_properties! {
     DUMMY_PROPERTIES,
         define_property!(
@@ -59,6 +66,7 @@ unsafe impl ObjectType for DummyState {
 impl ObjectImpl for DummyState {
     type ParentType = DeviceState;
     const ABSTRACT: bool = false;
+    const CLASS_INIT: fn(&mut DummyClass) = DummyClass::class_init::<Self>;
 }
 
 impl ResettablePhasesImpl for DummyState {}
@@ -72,14 +80,6 @@ impl DeviceImpl for DummyState {
     }
 }
 
-// `impl<T> ClassInitImpl<DummyClass> for T` doesn't work since it violates
-// orphan rule.
-impl ClassInitImpl<DummyClass> for DummyState {
-    fn class_init(klass: &mut DummyClass) {
-        <Self as ClassInitImpl<DeviceClass>>::class_init(&mut klass.parent_class);
-    }
-}
-
 #[derive(qemu_api_macros::offsets)]
 #[repr(C)]
 #[derive(qemu_api_macros::Object)]
@@ -101,20 +101,15 @@ unsafe impl ObjectType for DummyChildState {
 impl ObjectImpl for DummyChildState {
     type ParentType = DummyState;
     const ABSTRACT: bool = false;
+    const CLASS_INIT: fn(&mut DummyChildClass) = DummyChildClass::class_init::<Self>;
 }
 
 impl ResettablePhasesImpl for DummyChildState {}
 impl DeviceImpl for DummyChildState {}
 
-impl ClassInitImpl<DummyClass> for DummyChildState {
-    fn class_init(klass: &mut DummyClass) {
-        <Self as ClassInitImpl<DeviceClass>>::class_init(&mut klass.parent_class);
-    }
-}
-
-impl ClassInitImpl<DummyChildClass> for DummyChildState {
-    fn class_init(klass: &mut DummyChildClass) {
-        <Self as ClassInitImpl<DummyClass>>::class_init(&mut klass.parent_class);
+impl DummyChildClass {
+    pub fn class_init<T: DeviceImpl>(self: &mut DummyChildClass) {
+        self.parent_class.class_init::<T>();
     }
 }