rust: qdev: add clock creation

Add a Rust version of qdev_init_clock_in, which can be used in
instance_init.  There are a couple differences with the C
version:

- in Rust the object keeps its own reference to the clock (in addition to
  the one embedded in the NamedClockList), and the reference is dropped
  automatically by instance_finalize(); this is encoded in the signature
  of DeviceClassMethods::init_clock_in, which makes the lifetime of the
  clock independent of that of the object it holds.  This goes unnoticed
  in the C version and is due to the existence of aliases.

- also, anything that happens during instance_init uses the pinned_init
  framework to operate on a partially initialized object, and is done
  through class methods (i.e. through DeviceClassMethods rather than
  DeviceMethods) because the device does not exist yet.  Therefore, Rust
  code *must* create clocks from instance_init, which is stricter than C.

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

rust/hw/char/pl011/src/device.rs

@@ -10,17 +10,16 @@ use std::{
 
 use qemu_api::{
     bindings::{
-        error_fatal, hwaddr, memory_region_init_io, qdev_init_clock_in, qdev_prop_set_chr,
-        qemu_chr_fe_accept_input, qemu_chr_fe_ioctl, qemu_chr_fe_set_handlers,
-        qemu_chr_fe_write_all, qemu_irq, sysbus_connect_irq, sysbus_mmio_map, sysbus_realize,
-        CharBackend, Chardev, Clock, ClockEvent, MemoryRegion, QEMUChrEvent,
-        CHR_IOCTL_SERIAL_SET_BREAK,
+        error_fatal, hwaddr, memory_region_init_io, qdev_prop_set_chr, qemu_chr_fe_accept_input,
+        qemu_chr_fe_ioctl, qemu_chr_fe_set_handlers, qemu_chr_fe_write_all, qemu_irq,
+        sysbus_connect_irq, sysbus_mmio_map, sysbus_realize, CharBackend, Chardev, MemoryRegion,
+        QEMUChrEvent, CHR_IOCTL_SERIAL_SET_BREAK,
     },
     c_str, impl_vmstate_forward,
     irq::InterruptSource,
     prelude::*,
-    qdev::{DeviceImpl, DeviceState, Property},
-    qom::{ClassInitImpl, ObjectImpl, ParentField},
+    qdev::{Clock, ClockEvent, DeviceImpl, DeviceState, Property},
+    qom::{ClassInitImpl, ObjectImpl, Owned, ParentField},
     sysbus::{SysBusDevice, SysBusDeviceClass},
     vmstate::VMStateDescription,
 };
@@ -131,7 +130,7 @@ pub struct PL011State {
     #[doc(alias = "irq")]
     pub interrupts: [InterruptSource; IRQMASK.len()],
     #[doc(alias = "clk")]
-    pub clock: NonNull<Clock>,
+    pub clock: Owned<Clock>,
     #[doc(alias = "migrate_clk")]
     pub migrate_clock: bool,
 }
@@ -485,8 +484,6 @@ impl PL011State {
     /// location/instance. All its fields are expected to hold unitialized
     /// values with the sole exception of `parent_obj`.
     unsafe fn init(&mut self) {
-        const CLK_NAME: &CStr = c_str!("clk");
-
         // SAFETY:
         //
         // self and self.iomem are guaranteed to be valid at this point since callers
@@ -506,22 +503,16 @@ impl PL011State {
 
         // SAFETY:
         //
-        // self.clock is not initialized at this point; but since `NonNull<_>` is Copy,
-        // we can overwrite the undefined value without side effects. This is
-        // safe since all PL011State instances are created by QOM code which
-        // calls this function to initialize the fields; therefore no code is
-        // able to access an invalid self.clock value.
-        unsafe {
-            let dev: &mut DeviceState = self.upcast_mut();
-            self.clock = NonNull::new(qdev_init_clock_in(
-                dev,
-                CLK_NAME.as_ptr(),
-                None, /* pl011_clock_update */
-                addr_of_mut!(*self).cast::<c_void>(),
-                ClockEvent::ClockUpdate.0,
-            ))
-            .unwrap();
-        }
+        // self.clock is not initialized at this point; but since `Owned<_>` is
+        // not Drop, we can overwrite the undefined value without side effects;
+        // it's not sound but, because for all PL011State instances are created
+        // by QOM code which calls this function to initialize the fields, at
+        // leastno code is able to access an invalid self.clock value.
+        self.clock = self.init_clock_in("clk", &Self::clock_update, ClockEvent::ClockUpdate);
+    }
+
+    const fn clock_update(&self, _event: ClockEvent) {
+        /* pl011_trace_baudrate_change(s); */
     }
 
     fn post_init(&self) {

rust/qemu-api/src/prelude.rs

@@ -7,6 +7,8 @@ pub use crate::bitops::IntegerExt;
 pub use crate::cell::BqlCell;
 pub use crate::cell::BqlRefCell;
 
+pub use crate::qdev::DeviceMethods;
+
 pub use crate::qom::IsA;
 pub use crate::qom::Object;
 pub use crate::qom::ObjectCast;

rust/qemu-api/src/qdev.rs

@@ -4,14 +4,20 @@
 
 //! Bindings to create devices and access device functionality from Rust.
 
-use std::{ffi::CStr, ptr::NonNull};
+use std::{
+    ffi::{CStr, CString},
+    os::raw::c_void,
+    ptr::NonNull,
+};
 
-pub use bindings::{DeviceClass, DeviceState, Property};
+pub use bindings::{Clock, ClockEvent, DeviceClass, DeviceState, Property};
 
 use crate::{
     bindings::{self, Error},
+    callbacks::FnCall,
+    cell::bql_locked,
     prelude::*,
-    qom::{ClassInitImpl, ObjectClass},
+    qom::{ClassInitImpl, ObjectClass, Owned},
     vmstate::VMStateDescription,
 };
 
@@ -143,3 +149,98 @@ unsafe impl ObjectType for DeviceState {
         unsafe { CStr::from_bytes_with_nul_unchecked(bindings::TYPE_DEVICE) };
 }
 qom_isa!(DeviceState: Object);
+
+/// Trait for methods exposed by the [`DeviceState`] class.  The methods can be
+/// called on all objects that have the trait `IsA<DeviceState>`.
+///
+/// The trait should only be used through the blanket implementation,
+/// which guarantees safety via `IsA`.
+pub trait DeviceMethods: ObjectDeref
+where
+    Self::Target: IsA<DeviceState>,
+{
+    /// Add an input clock named `name`.  Invoke the callback with
+    /// `self` as the first parameter for the events that are requested.
+    ///
+    /// The resulting clock is added as a child of `self`, but it also
+    /// stays alive until after `Drop::drop` is called because C code
+    /// keeps an extra reference to it until `device_finalize()` calls
+    /// `qdev_finalize_clocklist()`.  Therefore (unlike most cases in
+    /// which Rust code has a reference to a child object) it would be
+    /// possible for this function to return a `&Clock` too.
+    #[inline]
+    fn init_clock_in<F: for<'a> FnCall<(&'a Self::Target, ClockEvent)>>(
+        &self,
+        name: &str,
+        _cb: &F,
+        events: ClockEvent,
+    ) -> Owned<Clock> {
+        fn do_init_clock_in(
+            dev: *mut DeviceState,
+            name: &str,
+            cb: Option<unsafe extern "C" fn(*mut c_void, ClockEvent)>,
+            events: ClockEvent,
+        ) -> Owned<Clock> {
+            assert!(bql_locked());
+
+            // SAFETY: the clock is heap allocated, but qdev_init_clock_in()
+            // does not gift the reference to its caller; so use Owned::from to
+            // add one.  The callback is disabled automatically when the clock
+            // is unparented, which happens before the device is finalized.
+            unsafe {
+                let cstr = CString::new(name).unwrap();
+                let clk = bindings::qdev_init_clock_in(
+                    dev,
+                    cstr.as_ptr(),
+                    cb,
+                    dev.cast::<c_void>(),
+                    events.0,
+                );
+
+                Owned::from(&*clk)
+            }
+        }
+
+        let cb: Option<unsafe extern "C" fn(*mut c_void, ClockEvent)> = if F::is_some() {
+            unsafe extern "C" fn rust_clock_cb<T, F: for<'a> FnCall<(&'a T, ClockEvent)>>(
+                opaque: *mut c_void,
+                event: ClockEvent,
+            ) {
+                // SAFETY: the opaque is "this", which is indeed a pointer to T
+                F::call((unsafe { &*(opaque.cast::<T>()) }, event))
+            }
+            Some(rust_clock_cb::<Self::Target, F>)
+        } else {
+            None
+        };
+
+        do_init_clock_in(self.as_mut_ptr(), name, cb, events)
+    }
+
+    /// Add an output clock named `name`.
+    ///
+    /// The resulting clock is added as a child of `self`, but it also
+    /// stays alive until after `Drop::drop` is called because C code
+    /// keeps an extra reference to it until `device_finalize()` calls
+    /// `qdev_finalize_clocklist()`.  Therefore (unlike most cases in
+    /// which Rust code has a reference to a child object) it would be
+    /// possible for this function to return a `&Clock` too.
+    #[inline]
+    fn init_clock_out(&self, name: &str) -> Owned<Clock> {
+        unsafe {
+            let cstr = CString::new(name).unwrap();
+            let clk = bindings::qdev_init_clock_out(self.as_mut_ptr(), cstr.as_ptr());
+
+            Owned::from(&*clk)
+        }
+    }
+}
+
+impl<R: ObjectDeref> DeviceMethods for R where R::Target: IsA<DeviceState> {}
+
+unsafe impl ObjectType for Clock {
+    type Class = ObjectClass;
+    const TYPE_NAME: &'static CStr =
+        unsafe { CStr::from_bytes_with_nul_unchecked(bindings::TYPE_CLOCK) };
+}
+qom_isa!(Clock: Object);

rust/qemu-api/src/vmstate.rs

@@ -470,11 +470,11 @@ macro_rules! vmstate_clock {
                 $crate::assert_field_type!(
                     $struct_name,
                     $field_name,
-                    core::ptr::NonNull<$crate::bindings::Clock>
+                    $crate::qom::Owned<$crate::bindings::Clock>
                 );
                 $crate::offset_of!($struct_name, $field_name)
             },
-            size: ::core::mem::size_of::<*const $crate::bindings::Clock>(),
+            size: ::core::mem::size_of::<*const $crate::qdev::Clock>(),
             flags: VMStateFlags(VMStateFlags::VMS_STRUCT.0 | VMStateFlags::VMS_POINTER.0),
             vmsd: unsafe { ::core::ptr::addr_of!($crate::bindings::vmstate_clock) },
             ..$crate::zeroable::Zeroable::ZERO