Re: [PATCH v12 net-next 03/11] bpf: add lookup/update/delete/iterate methods to BPF maps

On Tue, Sep 16, 2014 at 1:54 PM, David Miller [off-list ref] wrote:

The cost of the compat layer must be considered and weighted
against this cast, which I think is really no big deal.

quoted

I think compat layer is a better option.

It's overhead you'll have to support forever, I think you should
reconsider.

All of the "ugly casting" will be hidden, or can be hidden, in the
syscall wrappers and/or interfaces in userspace.

ahh, ok. I thought you're strongly against any type of casts.
In such case I can get rid of 'union bpf_attr' as well and simply
define a struct per command, then syscall will look like:
sys_bpf(int cmd, void __user *attr, unsigned int size);
and uapi/linux/bpf.h will have:
struct bpf_prog_load_attr { /* for BPF_PROG_LOAD cmd */
    __u32 prog_type;
    __u32 insn_cnt;
    __aligned_u64 insns;
    __aligned_u64 license;
    __u32 log_level;
    __u32 log_size;
    __aligned_u64 log_buf;
};
and similar for other commands.
no compat layer and type checking will be done
by syscall wrappers. Ok?