Re: [PATCH] rust: log: implement io::Write

[Zhao Liu <zhao1.liu@intel.com>]

>  /// A macro to log messages conditionally based on a provided mask.
> @@ -24,6 +96,8 @@ pub enum Log {
>  /// log level and, if so, formats and logs the message. It is the Rust
>  /// counterpart of the `qemu_log_mask()` macro in the C implementation.
>  ///
> +/// Errors from writing to the log are ignored.
> +///
>  /// # Parameters
>  ///
>  /// - `$mask`: A log level mask. This should be a variant of the `Log` enum.
> @@ -62,12 +136,9 @@ macro_rules! log_mask_ln {
>          if unsafe {
>              (::qemu_api::bindings::qemu_loglevel & ($mask as std::os::raw::c_int)) != 0
>          } {
> -            let formatted_string = format!("{}\n", format_args!($fmt $($args)*));
> -            let c_string = std::ffi::CString::new(formatted_string).unwrap();
> -
> -            unsafe {
> -                ::qemu_api::bindings::qemu_log(c_string.as_ptr());
> -            }
> +            #[allow(unused_must_use)]

I found this doesn't work :-( :

error: unused `Result` that must be used
   --> ../rust/hw/char/pl011/src/device.rs:281:21
    |
281 |                     log_mask_ln!(Log::Unimp, "pl011: DMA not implemented");
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: this `Result` may be an `Err` variant, which should be handled
    = note: `-D unused-must-use` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(unused_must_use)]`
    = note: this error originates in the macro `log_mask_ln` (in Nightly builds, run with -Z macro-backtrace for more info)

I understand meson sets `-D warings` so that `allow` can't work...

What about just ignoring the return value? Afterall pl011 doesn't care
the returned value.

@@ -136,8 +137,7 @@ macro_rules! log_mask_ln {
         if unsafe {
             (::qemu_api::bindings::qemu_loglevel & ($mask as std::os::raw::c_int)) != 0
         } {
-            #[allow(unused_must_use)]
-            ::qemu_api::log::LogGuard::log_fmt(
+            let _ = ::qemu_api::log::LogGuard::log_fmt(
                 format_args!("{}\n", format_args!($fmt $($args)*)));
         }
     }};

Thanks,
Zhao

> +            ::qemu_api::log::LogGuard::log_fmt(
> +                format_args!("{}\n", format_args!($fmt $($args)*)));
>          }
>      }};
>  }
> -- 
> 2.49.0
> 
>