[ovs-dev] [ext-260 v3 4/5] ofp-errors: Implement OpenFlow 1.2+ experimenter error codes.

[Alex Wang]

> > > > "
> > > >         oem = ofpbuf_put_uninit(buf, sizeof *oem);
> > > >         oem->type = htons(NXET_VENDOR);
> > > > "
> > > >
> > > > In the "ovs_hex_dump()" function which prints the encoded header, it
> uses
> > > > "fprintf(stream, "%02hhx"
> > > > to print it and the value is again in host order (if %x is used, it
> will
> > > > print the network order).
> > > >
> > > > So I want to ask what is the use of "hhx" here? and why can't we get
> rid
> > > of
> > > > htons and use %x in
> > > > ovs_hex_dump?
> > >
> > > 'oem' is a "wire format" type, and its member 'type' is an ovs_be16,
> > > so to appropriately assign it a value it must be converted to network
> > > byte order first.  That is why htons() is used.
> > >
> > > ovs_hex_dump() dumps the contents of a structure byte by byte.  Its
> > > output will depend on the byte order of the underlying data.  In this
> > > case the data is in network byte order, so the byte-by-byte dump will
> > > reflect that.
> > >
> > > 'hh' doesn't have anything to do with byte order.  It means that the
> > > argument is a char type.
> > >
> >
> >
> > Thanks for the explanation. My previous experiment was wrong. And I found
> > out that the if "htons" is not used the "0xb0c2" when converted to "uint8
> > buf[2]" will be "buf[0]=0xc2" and "buf[1]=0xb0". So I think the "htons"
> > also helps preserve the hex order. right?
>
> It depends on the machine's endianness.  You're using x86 or x86-64 (I
> guess), which is little-endian, so you see what you're reporting.  If
> you were using a SPARC or some other big-endian machine, the htons()
> would have no effect and you would see no difference, because host and
> network byte order are the same on a big-endian machine.
>

Thanks Ben,

This makes sense,
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