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Add Debug trait implementation for ReadOnly, WriteOnly, and Volatile #126

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Add Debug trait implementation for ReadOnly, WriteOnly, and Volatile #126

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1 change: 1 addition & 0 deletions src/transport/mmio.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,7 @@ impl Display for MmioError {
///
/// Ref: 4.2.2 MMIO Device Register Layout and 4.2.4 Legacy interface
#[repr(C)]
#[derive(Debug)]
pub struct VirtIOHeader {
/// Magic value
magic: ReadOnly<u32>,
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20 changes: 20 additions & 0 deletions src/volatile.rs
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Expand Up @@ -3,6 +3,12 @@
#[repr(transparent)]
pub struct ReadOnly<T: Copy>(T);

impl<T: Debug + Copy> Debug for ReadOnly<T> {
fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
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No need for the explicit lifetime <'_> here and in the other implementation below.

f.debug_tuple("ReadOnly").field(&self.0).finish()
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ReadOnly is intended to wrap MMIO registers which may have side-effects when reading, so it's probably not a good idea to implement Debug, as adding debug output may change behaviour. Also any reading should be done with read_volatile.

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Indeed, you are right, I didn't consider the issue of side effects.

}
}

impl<T: Copy> ReadOnly<T> {
/// Construct a new instance for testing.
pub fn new(value: T) -> Self {
Expand All @@ -15,6 +21,12 @@ impl<T: Copy> ReadOnly<T> {
#[repr(transparent)]
pub struct WriteOnly<T: Copy>(T);

impl<T: Debug + Copy> Debug for WriteOnly<T> {
fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
f.debug_tuple("WriteOnly").field(&self.0).finish()
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WriteOnly is used to wrap MMIO registers which can only be written, so it doesn't make sense to read a value from it.

}
}

/// An MMIO register which may be both read and written.
#[derive(Default)]
#[repr(transparent)]
Expand All @@ -27,6 +39,12 @@ impl<T: Copy> Volatile<T> {
}
}

impl<T: Debug + Copy> Debug for Volatile<T> {
fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
f.debug_tuple("Volatile").field(&self.0).finish()
}
}

/// A trait implemented by MMIO registers which may be read from.
pub trait VolatileReadable<T> {
/// Performs a volatile read from the MMIO register.
Expand Down Expand Up @@ -104,5 +122,7 @@ macro_rules! volwrite {
};
}

use core::fmt::{Debug, Formatter};
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Put these imports at the top of the file.


pub(crate) use volread;
pub(crate) use volwrite;
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