Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!apple!chuq
From: chuq@Apple.COM (Chuq Von Rospach)
Newsgroups: comp.protocols.nfs
Subject: Re: what causes a stale file handle?
Message-ID: <34618@apple.Apple.COM>
Date: 10 Sep 89 02:58:43 GMT
References: <89Sep9.212500edt.2173@neat.cs.toronto.edu>
Organization: Life is just a Fantasy novel played for keeps
Lines: 46

>Question:

>Why is the stale NFS handle error returned?  Any way to compensate within
>the daemon apart from doing a close()/open() sequence?  Any way to tell
>that a read() will return ESTALE without actually doing the read() ?

A stale file handle is reported when the Fhandle to the file in question
becomes out of date. Every inode on an NFS-server has a generation count
that is modified whenever that inode is re-used (or whenever fsirand is run,
like when you run newfs).

What's probably happening to you, since this is a news partition, is that
expire is being run. As part of expire, a new active file is created, then
there's a renaming of active to oactive and nactive to active. Your daemon
now has an fhandle pointing to what is now oactive.

Since NFS is stateless, the fhandle has a generation count to avoid the
following scenario:

o client opens server:/tmp/foo
o server deletes /tmp/foo
o server creates new file /tmp/financial_data (which happens to re-use the
  same inode)
o client attempts to use the fhandle given it by /tmp/foo. Without the
  generation count, since the fhandle would point to an inode with a real
  file attached, the access would succeed, even though the file you opened
  has nothing to do with the data you are now playing with.

Generally, you'll see stale fhandles under two circumstances:

o the filesystem you have mounted gets restored from backup and you haven't
  umounted it.
o the file you have open has been deleted and re-created.

the stale message is a way of telling you that something has happened to the
file since you opened it that makes the fhandle you have invalid, so you
don't continue using an fhandle that may well be pointing to incorrect data.


-- 

Chuq Von Rospach      <+>     Editor,OtherRealms     <+>     Member SFWA/ASFA
         chuq@apple.com   <+>  CI$: 73317,635  <+>  AppleLink: CHUQ
      [This is myself speaking. No company can control my thoughts.]

        Perhaps I should say Dr. *Von* Rospach, Dr. Rospach? (Gasp)