Am 31. März 2025 09:53:41 UTC schrieb Paolo Bonzini <pbonz...@redhat.com>:
>On 3/30/25 22:58, Bernhard Beschow wrote:
>> A qemu_log_mask!() macro is provided which expects similar arguments as the C
>> version. However, the formatting works as one would expect from Rust.
>>
>> To maximize code reuse the macro is just a thin wrapper around qemu_log().
>> Also, just the bare minimum of logging masks is provided which should suffice
>> for the current use case of Rust in QEMU.
>
>It's probably better to use an enum for this. One possibility is also to
>change the #defines to a C enum, and see which enum translation of the several
>allowed by bindgen is best.
Currently the #defines contain some holes for "private" mask bits. Turning
these into an enum without exposing all publicly, and changing the type of
qemu_loglevel for consistency, would result in undefined behavior. Or do you
suggest to convert just the public #defines into an enum to expose them to
Rust, and keep the rest of the C API including the type of qemu_loglevel as is?
There are surely several tradeoffs and/or cleanups possible here, but that's
way beyond for what I wanted to achieve -- which is closing a gap between C and
Rust. My main goal is just to get my feet wet with Rust.
>
>Also, while this is good for now, later on we probably want to reimplement
>logging at a lower level via the std::fmt::Write trait. But that's just for
>efficiency and your macro is indeed good enough to define what the API would
>look like.
Can we live with an easy solution then for now? As you suggest below, further
abstractions like log_guest_error! can be built on top which further insulates
client code from implementation details such as the representation of the mask
bits.
> Right now I have a project for GSoC that will look at that, and the student
> can look into it later on.
Whoops, I didn't intend to spoil the project.
>
>This means answering the following two questions:
>
>- the mapping the LOG_* constants into Rust
>
>- whether to keep the "qemu" prefix for the API (personal opinion: no)
>
>- whether it makes sense to add more macros such as log_guest_error! or
>log_unimp! for the most common LOG_* values
>
>> +#[macro_export]
>> +macro_rules! qemu_log_mask {
>> + ($mask:expr, $fmt:expr $(, $args:expr)*) => {{
>
>Looking at https://doc.rust-lang.org/std/macro.write.html they just use
>$($arg:tt)* for what is passed to format_args! (or in your case format!), so
>we can do the same here too. The main advantage is that it allows giving a
>trailing comma to qemu_log_mask!.
Easy to fix. Before proceeding I'd like to see a solution for the topic above.
Best regards,
Bernhard
>
>Paolo
>
>> + if unsafe {
>> + (::qemu_api::bindings::qemu_loglevel & ($mask as
>> std::os::raw::c_int)) != 0
>> + } {
>> + let formatted_string = format!($fmt, $($args),*);
>> + let c_string =
>> std::ffi::CString::new(formatted_string).unwrap();
>> +
>> + unsafe {
>> + ::qemu_api::bindings::qemu_log(c_string.as_ptr());
>> + }
>> + }
>> + }};
>> +}
>
