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To: Andi Kleen <ak@suse.de>
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Subject: Re: [PATCH] zerocopy NFS updated
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From: ebiederm@xmission.com (Eric W. Biederman)
Date: 13 Apr 2002 13:19:46 -0600
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Andi Kleen <ak@suse.de> writes:

> > I wonder if it is reasonable to depend on that: -- i.e. I'll only ever
> > see zeros, not say random bytes, or ones or something.  I'm sure that's
> > so with the current kernel, and probably all of them ever (except for
> > bugs) but I wonder whether it's ok to rely on that.
> 
> With truncates you should only ever see zeros. If you want this guarantee
> over system crashes you need to make sure to use the right file system
> though (e.g. ext2 or reiserfs without the ordered data mode patches or
> ext3 in writeback mode could give you junk if the system crashes at the
> wrong time). Still depending on only seeing zeroes would
> seem to be a bit fragile on me (what happens when the disk dies for 
> example?), using some other locking protocol is probably more safe.

Could the garbage from ext3 in writeback mode be considered an
information leak?  I know that is why most places in the kernel
initialize pages to 0.  So you don't accidentally see what another
user put there.

Eric
k
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