From mboxrd@z Thu Jan  1 00:00:00 1970
From: ron@ronnatalie.com (Ron Natalie)
Date: Thu, 25 Jan 2018 14:36:15 -0500
Subject: [TUHS] V6 UNIX main() oddness
In-Reply-To: <20180125184259.8B62518C0B0@mercury.lcs.mit.edu>
References: <20180125184259.8B62518C0B0@mercury.lcs.mit.edu>
Message-ID: <033501d39613$c3f86fa0$4be94ee0$@ronnatalie.com>

I don't see any reason why you can't make that optimization at that point.
Nothing is going to come in and suddenly invalidate the inode between those
two lines.
I suspect it was an example of cut/paste-it is from some other part of the
kernel.

-----Original Message-----
From: TUHS [mailto:tuhs-bounces@minnie.tuhs.org] On Behalf Of Noel Chiappa
Sent: Thursday, January 25, 2018 1:43 PM
To: tuhs at minnie.tuhs.org
Cc: jnc at mercury.lcs.mit.edu
Subject: [TUHS] V6 UNIX main() oddness

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