Seems reasonable to me give the code path and time its being called. Maybe left over from hacking from an earlier kernel requirement and never noticed by Ken. I wonder if the mount table had been set up in some earlier scheme and he wanted to make sure it was checked first. That's the only thing that seems logical, but we all miss optimizations.

On Thu, Jan 25, 2018 at 1:42 PM, Noel Chiappa <jnc@mercury.lcs.mit.edu> wrote:

So, while bringing up V6 on a hardware PDP-11/23 with an RK11 emulator using
an SD card for storage which Dave Bridgham and I are doing, I found this piece
of code in main() on V6 Unix:

rootdir = iget(rootdev, ROOTINO);
rootdir->i_flag =& ~ILOCK;
u.u_cdir = iget(rootdev, ROOTINO);
u.u_cdir->i_flag =& ~ILOCK;

I don't get why two separate calls to iget(), with the same arguments;
why not replace the second pair of lines with:

u.u_cdir = rootdir;
rootdir->i_count++;

What am I missing?

Noel