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Date: Thu, 30 May 1996 20:11:19 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199605301011.UAA14948@godzilla.zeta.org.au>
To: rashid@rk.ios.com, terry@lambert.org
Subject: Re: Breaking ffs - speed enhancement?
Cc: davidg@Root.COM, hackers@freebsd.org, jgreco@solaria.sol.net
Sender: owner-hackers@freebsd.org
X-Loop: FreeBSD.org
Precedence: bulk

>There is a school of thought that says "shall be updated" in POSIX is
>not the same as "shall be committed to stable storage" (the traditional
>BSD implementation).

When was this traditional?

>This would let access times be updated in core, but only scheduled to
>be written at a later time (not forced out immediately).

4.4BSD and I think Net/2 always only scheduled them to be written at a
later time.  At the end of every read (incorrectly including unsuccessful
ones), access times are marked for update:

	ip->i_flag |= IN_ACCESS;	/* see ufs_readwrite.c */

At certain checkpoints, the access times are updated.  E.g., in ufs_close()

	if (inuse && !locked)
		ITIMES(ip, &time, &time);

If IN_ACCESS is set, this sets the access time in-core, sets IN_MODIFIED, and
clears IN_ACCESS.  It doesn't write the inode.  Setting IN_MODIFIED schedules
the inode to be written on the next sync, or when it is reused.  ffs_sync()
calls VOP_UPDATE() with the sync-update flag clear and ffs_update() schedules
a delayed write.

Bruce