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From: Terry Lambert <terry@lambert.org>
Newsgroups: comp.unix.bsd.freebsd.misc,comp.os.linux.development.system
Subject: Re: The better (more suitable)Unix?? FreeBSD or Linux
Date: 26 Feb 1996 20:54:35 GMT
Organization: Utah Valley State College, Orem, Utah
Lines: 37
Message-ID: <4gt6mb$pv@park.uvsc.edu>
References: <4er9hp$5ng@orb.direct.ca> <311C5EB4.2F1CF0FB@freebsd.org> <CBITMEAD.96Feb26173656@versant.versant.com.au>
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Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:14629 comp.os.linux.development.system:18377
cbitmead@versant.versant.com.au wrote:
] >Sync metadata is an implementation of ordered writes. It's
] >about as trivial an implementation as you can possibly devise,
] >but it *is* one.
]
] Except that it is the wrong order. The correct way is to write the
] data first and then the meta-data. This ensures consistent data.
How, in your proposed implementation, would you distinguish
allocated blocks that have been written from allocated blocks
that have not been written in a two user delete/create case?
Which is to say, Bob deletes file "foo", Jim copies secure file
"fum", writes some sensitive data to "fum" in a block that belonged
to "foo", and the system crashes before "foo" is really deleted.
Bob comes in and says "hmmm... I thought I deleted that, and
looks at the contents tosee why he decided to not delete the
file.
And sees Jim's sensitive data.
The "wrong" order argument is dependent on you not knowing about
synchronous bitmap updates after async data block writes. Haven't
you read the other postings in this thread, or are you just
commenting to defend your religion?
Please (re)read the FFS paper.
PS: please trim your quotes.
Terry Lambert
terry@cs.weber.edu
---
Any opinions in this posting are my own and not those of my present
or previous employers.