From: Alexei Starovoitov
> On Tue, Jan 6, 2015 at 6:05 PM, Thomas Graf <tg...@suug.ch> wrote:
> > +struct vxlan_gbp {
> > +#ifdef __LITTLE_ENDIAN_BITFIELD
> > + __u8 reserved_flags1:3,
> ...
> > + __be16 policy_id;
> > +} __packed;
>
> are you sure that compiler will be smart enough
> to do single short load when you pack
> u8 + struct vxlan_gbp inside struct vxlanhdr ?
> I suspect compiler will use two byte loads
> with shifts and ors every time to access policy_id.
> Even it works ok, I think this struct layout is ugly.
> imo would be much easier to read if you replace
> the whole vxlanhdr with vxlanhdr_gbp
> or split vxlanhdr into two 32-bit structs.
> then __packed hacks won't be needed.
Also, if you are writing the values then you need to write
all the members of the bitfield in order to get a single write.
Basically you are much better off using explicit masks.
David
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