Re: [RFC 3/6] scripts/simpletrace-rust: Add helpers to parse trace file

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

> > +    fn read_type(mut fobj: &File) -> Result<RecordType>
> > +    {
> > +        let mut tbuf = [0u8; 8];
> > +        if let Err(e) = fobj.read_exact(&mut tbuf) {
> > +            if e.kind() == ErrorKind::UnexpectedEof {
> > +                return Ok(RecordType::Empty);
> > +            } else {
> > +                return Err(Error::ReadFile(e));
> > +            }
> > +        }
> > +
> > +        /*
> > +         * Safe because the layout of the trace record requires us to parse
> > +         * the type first, and then there is a check on the validity of the
> > +         * record type.
> > +         */
> > +        let raw_t =
> > +            unsafe { std::mem::transmute::<[u8; 8], RecordRawType>(tbuf) };
> 
> A safe alternative: https://doc.rust-lang.org/std/primitive.u64.html#method.from_ne_bytes?

Thanks! Will use it.

> > +        match raw_t.rtype {
> > +            RECORD_TYPE_MAPPING => Ok(RecordType::Mapping),
> > +            RECORD_TYPE_EVENT => Ok(RecordType::Event),
> > +            _ => Err(Error::UnknownRecType(raw_t.rtype)),
> > +        }
> > +    }
> > +}

[snip]

> > +{
> > +    fn read_header(mut fobj: &File) -> Result<Self>
> > +    {
> > +        let mut raw_hdr = [0u8; 24];
> > +        fobj.read_exact(&mut raw_hdr).map_err(Error::ReadFile)?;
> > +
> > +        /*
> > +         * Safe because the size of log header (struct LogHeader)
> > +         * is 24 bytes, which is ensured by simple trace backend.
> > +         */
> > +        let hdr =
> > +            unsafe { std::mem::transmute::<[u8; 24], LogHeader>(raw_hdr) };
> 
> Or u64::from_ne_bytes() for each field.

Will do.

> > +        Ok(hdr)
> > +    }
> > +}

[snip]

> > +impl ReadHeader for RecordHeader
> > +{
> > +    fn read_header(mut fobj: &File) -> Result<Self>
> > +    {
> > +        let mut raw_hdr = [0u8; 24];
> > +        fobj.read_exact(&mut raw_hdr).map_err(Error::ReadFile)?;
> > +
> > +        /*
> > +         * Safe because the size of record header (struct RecordHeader)
> > +         * is 24 bytes, which is ensured by simple trace backend.
> > +         */
> > +        let hdr: RecordHeader =
> > +            unsafe { std::mem::transmute::<[u8; 24], RecordHeader>(raw_hdr) };
> 
> Or u64::from_ne_bytes() and u32::from_ne_bytes() for all fields.

Will do.

Thanks,
Zhao