IFEF_MPSAFE

[Ryota Ozaki <ozaki.ryota%gmail.com@localhost>]

Hi,

http://www.netbsd.org/~ozaki-r/IFEF_MPSAFE.diff

I'm going to commit the above change that integrates
IFEF_OUTPUT_MPSAFE and IFEF_START_MPSAFE flags into
IFEF_MPSAFE.

The motivation is to not waste if_extflags bits. I'm now
trying to make if_ioctl() hold KERNEL_LOCK selectively
for some reasons as well as if_start() and if_output().
But adding one more flag for if_ioctl() is I think
wasteful. Also there are other functions such as if_init()
and if_slowtimo() that would also need a flag.

So I propose to have just one flag for indications of
MP-safe. If an interface have both MP-safe and non-MP-safe
operations at a time, we have to set the IFEF_MPSAFE flag
and let callees of non-MP-safe operations take KERNEL_LOCK.

This change breaks ABI and need a kernel version bump,
however, IFEF_*_MPSAFE flags are new to netbsd-8 so it
doesn't break backward compatibility.

Any comments or objections?

Thanks,
  ozaki-r