[v2,0/2] rust: safe wrappers for interrupt sources

Message

Paolo Bonzini Dec. 2, 2024, 11:06 a.m. UTC

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.  The code for BqlCell is a bit long but most of
it is lifted from the standard library and almost half is documentation,
including doctests.

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.
This is not added here because there is no use case (yet), but Zhao
is going to use it for his HPET implementation.

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 be
better left to Meson itself.

Paolo

v1->v2:
- change debug_assert to assert
- clarify meaning of active-high
- allow declaring vectored interrupt source
- fix documentation wrt threading rules

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        | 298 +++++++++++++++++++++++++++++++
 rust/qemu-api/src/irq.rs         |  91 ++++++++++
 rust/qemu-api/src/lib.rs         |   3 +
 rust/qemu-api/src/sysbus.rs      |  26 +++
 6 files changed, 433 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