On 17-04-17 10:58 AM, Eric Dumazet wrote: [..]
Very often, pads are there because of ABI constraints.We 'name' them to make clear to developers that they are there, and avoid security issues, because of say few bytes from kernel stack are copied to user space. struct foo { __u32 a; __u16 b; }; Note that the 16bit padding is there, even if you do not name it.
Agreed. But note netlink is defined as "a wire protocol" which has explicit requirement to pad/align to 32 bit boundary. Therefore we _always_ explicitly name the pads.
Once this structure had been exported to some include file and in a kernel, there is little point trying to 'reuse' the padding, unless for very specific cases. If you name paddings, then developers might think about it.
We always name them for netlink. The challenge is a few months later we are not allowed to use the fields we name. I see these netlink struct pads in the same manner as say reserved packet header fields. cheers, jamal
