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Date:      Fri, 7 Aug 1998 07:27:34 +0000 (GMT)
From:      Terry Lambert <tlambert@primenet.com>
To:        poipoi@famipow.com
Cc:        freebsd-fs@FreeBSD.ORG
Subject:   Re: inode version?
Message-ID:  <199808070727.AAA22692@usr08.primenet.com>
In-Reply-To: <19980807061557.268.qmail@hwi.poi.org> from "poipoi@famipow.com" at Aug 7, 98 08:15:57 am

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> in vfs implementation, i see a inode version but i dont understand what
> is it... according to some books, it is used for NFS but i understand
> how and why.

It is used to tell the difference between an inode that is rereferenced
in a stateless protocol and an inode that is rereferenced after it has
been reused.  If it has been reused, it's just as valid as before, but
if the generation count is different, it's stale.

This is used to recover from the case where an inode reference count
goes to zero on an NFS server when the file is held open over a
delete.

Because you can't set VEXEC on the server from the client, in a memory
overcommit architecture (where the file is used as a swap store), a file
may "disappear" out from under you.  If this happens, the generation
number changes, and you can tell that it happened, and fail more
gracefully than you would have oherwise.


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

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