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From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.unix.wizards
Subject: Re: BSD vi/view resets inode ctime: why?
Message-ID: <5718@mimsy.UUCP>
Date: Mon, 9-Mar-87 12:23:14 EST
Article-I.D.: mimsy.5718
Posted: Mon Mar  9 12:23:14 1987
Date-Received: Tue, 10-Mar-87 06:32:59 EST
References: <4801@brl-adm.ARPA>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 45

In article <4801@brl-adm.ARPA> rex@erebus (Rex Sanders) writes:
>Why does 4.2/4.3 BSD vi/view, exited without changing the file, update the
>inode change time?

(If you saw an earlier answer from me, ignore it.  I was suffering from
brain rot at the time.  I think I cancelled it before it got far.  This
version is right.  I think.)

In /usr/src/ucb/ex_io.c, one finds a routine called iostats().  This
routine is called just after reading or writing any file.  It does this:

	(void) fsync(io);
	close(io);

In /sys/sys/ufs_syscalls.c, we find fsync():

	fp = getinode(uap->fd);
	if (fp == NULL)
		return;
	ip = (struct inode *)fp->f_data;
	ILOCK(ip);
	syncip(ip);
	IUNLOCK(ip);

Note that there is no verification that the file is open for writing.
(Perhaps this is by design.)  In /sys/sys/ufs_inode.c, at the end of
syncip(), there is this code:

	ip->i_flag |= ICHG;
	iupdat(ip, &time, &time, 1);

which sets to `now' the inode change time (and, if the inode has
been previously marked, the access and update times).  One might
argue that this is unnecessary: but I am uncertain.  Again, this
may be by design.

By far the easiest fix is to change vi.  In ex_io.c, find the two
calls to iostats(), and add a `dosync' parameter, or move the
fsync() call to just before the call from the file-writing code.
Another possible fix, if it is deemed correct, would be to ensure
that (fp->f_flag & FWRITE) != 0.  Then vi's fsync() in the read
case would silently fail.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
UUCP:	seismo!mimsy!chris	ARPA/CSNet:	chris@mimsy.umd.edu