On Fri, Jan 17, 2025 at 08:39:56PM +0100, Paolo Bonzini wrote:
> Date: Fri, 17 Jan 2025 20:39:56 +0100
> From: Paolo Bonzini <pbonz...@redhat.com>
> Subject: [PATCH 03/10] rust: qom: add object creation functionality
> X-Mailer: git-send-email 2.47.1
>
> The basic object lifecycle test can now be implemented using safe code!
>
> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
> ---
> rust/hw/char/pl011/src/device.rs | 13 ++++++++-----
> rust/qemu-api/src/prelude.rs | 1 +
> rust/qemu-api/src/qom.rs | 23 +++++++++++++++++++++--
> rust/qemu-api/tests/tests.rs | 30 +++++++++++-------------------
> 4 files changed, 41 insertions(+), 26 deletions(-)
>
> diff --git a/rust/hw/char/pl011/src/device.rs
> b/rust/hw/char/pl011/src/device.rs
> index 27563700665..d8409f3d310 100644
> --- a/rust/hw/char/pl011/src/device.rs
> +++ b/rust/hw/char/pl011/src/device.rs
> @@ -690,15 +690,18 @@ pub fn post_load(&self, _version_id: u32) -> Result<(),
> ()> {
> irq: qemu_irq,
> chr: *mut Chardev,
> ) -> *mut DeviceState {
> + let pl011 = PL011State::new();
> unsafe {
> - let dev: *mut DeviceState = qdev_new(PL011State::TYPE_NAME.as_ptr());
> - let sysbus: *mut SysBusDevice = dev.cast::<SysBusDevice>();
> -
> + let dev = pl011.as_mut_ptr::<DeviceState>();
> qdev_prop_set_chr(dev, c_str!("chardev").as_ptr(), chr);
> - sysbus_realize_and_unref(sysbus, addr_of_mut!(error_fatal));
> +
> + let sysbus = pl011.as_mut_ptr::<SysBusDevice>();
> + sysbus_realize(sysbus, addr_of_mut!(error_fatal));
> sysbus_mmio_map(sysbus, 0, addr);
> sysbus_connect_irq(sysbus, 0, irq);
> - dev
> +
> + // return the pointer, which is kept alive by the QOM tree; drop
> owned ref
> + pl011.as_mut_ptr()
The ref count of Owned<> is decreased on exit, so we need to use
sysbus_realize() instead of sysbus_realize_and_unref() to ensure ref
count is correct at C side.
Initially, I hesitated here for an entire morning because this didn't
seem to conform to the usual usage of sysbus_realize_and_unref() (or,
further, qdev_realize_and_unref()).
But now I realize that qdev_realize() is used for embedded objects,
while qdev_realize_and_unref() is used for non-embedded cases. Therefore,
moving forward, perhaps qdev_realize_and_unref() should not exist on the
Rust side.
Owned<> will automatically drop and thus automatically unref, while
Child<> will not unref. Based on this consideration, I am now convincing
myself that this change (using sysbus_realize()) is reasonable. :-)
In the future, maybe we need some wrappers on qdev_realize()/sysbus_realize().
> }
> }
Overall, still fine for me,
Reviewed-by: Zhao Liu <zhao1....@intel.com>
