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Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Add a derive macro that makes it easy to peel off all the layers of
specialness (UnsafeCell, MaybeUninit, etc.) and just get a pointer
to the wrapped type; and likewise add them back starting from a
*mut.
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Inspired by the same-named type in Linux. This type provides the compiler
with a correct view of what goes on with FFI types. In addition, it
separates the glue code from the bindgen-generated code, allowing
traits such as Send, Sync or Zeroable to be specified independently
for C and Rust structs.
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Right now, the stub BQL in stubs/iothread-lock.c always reports itself as
unlocked. However, Rust would like to run its tests in an environment where
the BQL *is* locked. Provide an extremely dirty function that flips the
return value of bql_is_locked() to true.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Similar to the existing BqlCell, introduce a custom interior mutability
primitive that resembles RefCell but accounts for QEMU's threading model.
Borrowing the RefCell requires proving that the BQL is held, and
attempting to access without the BQL is a runtime panic.
Almost all of the code was taken from Rust's standard library, while
removing unstable features and probably-unnecessary functionality that
amounts to 60% of the original code. A lot of what's left is documentation,
as well as unit tests in the form of doctests. These are not yet integrated
in "make check" but can be run with "cargo test --doc".
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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QEMU objects usually have their pointer shared with the "outside
world" very early in their lifetime, for example when they create their
MemoryRegions. Because at this point it is not valid anymore to
create a &mut reference to the device, individual parts of the
device struct must be made mutable in a controlled manner.
QEMU's Big Lock (BQL) effectively turns multi-threaded code into
single-threaded code while device code runs, as long as the BQL is not
released while the device is borrowed (because C code could sneak in and
mutate the device). We can then introduce custom interior mutability primitives
that are semantically similar to the standard library's (single-threaded)
Cell and RefCell, but account for QEMU's threading model. Accessing
the "BqlCell" or borrowing the "BqlRefCell" requires proving that the
BQL is held, and attempting to access without the BQL is a runtime panic,
similar to RefCell's already-borrowed panic.
With respect to naming I also considered omitting the "Bql" prefix or
moving it to the module, e.g. qemu_api::bql::{Cell, RefCell}. However,
this could easily lead to mistakes and confusion; for example rustc could
suggest the wrong import, leading to subtle bugs.
As a start introduce the an equivalent of Cell. Almost all of the code
was taken from Rust's standard library, while removing unstable features
and probably-unnecessary functionality that constitute a large of the
original code. A lot of what's left is documentation, as well as unit
tests in the form of doctests. These are not yet integrated in "make
check" but can be run with "cargo test --doc".
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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