[PATCH 0/2] rust: safe wrappers for interrupt sources

[Paolo Bonzini <pbonzini@redhat.com>]

Interrupt sources, qemu_irq in C code, are pointers to IRQState objects.
They are QOM link properties and can be written to outside the control
of the device (i.e. from a shared reference); therefore their Rust
representation must be an interior-mutable field.

This make interrupt sources similar to a Cell<*mut IRQState>.  However,
a Cell can only live within one thread, while here the semantics are
"accessible by multiple threads but only under the Big QEMU Lock".

Therefore, this series adds to QEMU a specialized cell type that checks
locking rules with respect to the "Big QEMU Lock".  In particular,
qemu_api::cell::BqlCell only allows get()/set() under BQL protection and
therefore is Send/Sync.  It comes with documentation and doctests.
I am not fully satisfied with the solution I used for mocking the BQL;
I have a prototype that runs doctests from "meson test" but that may
take some more time to cook.

Likewise, qemu_api::cell::RefCell would be a RefCell that is Send/Sync,
because it checks that borrow()/borrow_mut() is only done under BQL;
but this is not added here because there is no use case (yet).

The interrupt sources prat was previously posted as RFC at
https://lore.kernel.org/qemu-devel/20241104085159.76841-1-pbonzini@redhat.com/,
while the BqlCell is new.  The code is a bit long but most of it is
lifted from the standard library and almost half is documentation.

Please review!

Paolo Bonzini (2):
  rust: add BQL-enforcing Cell variant
  rust: add bindings for interrupt sources

 rust/hw/char/pl011/src/device.rs |  22 +--
 rust/qemu-api/meson.build        |   3 +
 rust/qemu-api/src/cell.rs        | 294 +++++++++++++++++++++++++++++++
 rust/qemu-api/src/irq.rs         |  66 +++++++
 rust/qemu-api/src/lib.rs         |   3 +
 rust/qemu-api/src/sysbus.rs      |  26 +++
 6 files changed, 404 insertions(+), 10 deletions(-)
 create mode 100644 rust/qemu-api/src/cell.rs
 create mode 100644 rust/qemu-api/src/irq.rs
 create mode 100644 rust/qemu-api/src/sysbus.rs

-- 
2.47.0