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From: Terry Lambert <terry@lambert.org>
Message-Id: <199701141754.KAA00177@phaeton.artisoft.com>
Subject: Re: truss, trace ??
To: lada@ws2301.gud.siemens.co.at (Hr.Ladavac)
Date: Tue, 14 Jan 1997 10:54:57 -0700 (MST)
Cc: avalon@coombs.anu.edu.au, terry@lambert.org, stesin@gu.net,
        karpen@ocean.campus.luth.se, hackers@freebsd.org
In-Reply-To: <199701141034.AA263998091@ws2301.gud.siemens.co.at> from "Hr.Ladavac" at Jan 14, 97 11:34:50 am
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> There is a rather simple way to satisfy most of these semantic requirements:
> replace the leading blocks with holes--the file grows in the length, lseek
> works as expected, but write is only guaranteed to succeed if it
> fails in the last part of the file, and the filesystem occupancy does not
> increase.  read succeeds always, but sometimes it returns a buffer full of 
> (leading) zeros.

This works, until you realize that you run linearly forward through
the log file.

I assume you steal space in the inode to store the offset of the first
valid block in the file?  A log file may very well contain valid NULL
data... indistinguishable from a zero-fill block coming from the read
of a hole.

This does not address log files with internal structure boundries that
do not allign to disk block boundries.  Like wtmp.


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.