Message-ID: <3FBD328C.1070607@techsource.com>
Date: Thu, 20 Nov 2003 16:30:52 -0500
From: Timothy Miller <miller@techsource.com>
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To: Andreas Dilger <adilger@clusterfs.com>
CC: Justin Cormack <justin@street-vision.com>,
       Jesse Pollard <jesse@cats-chateau.net>,
       linux-kernel mailing list <linux-kernel@vger.kernel.org>
Subject: Re: OT: why no file copy() libc/syscall ??
References: <1068512710.722.161.camel@cube> <03111209360001.11900@tabby> <20031120172143.GA7390@deneb.enyo.de> <03112013081700.27566@tabby> <1069357453.26642.93.camel@lotte.street-vision.com> <3FBD27A0.50803@techsource.com> <20031120140739.I20568@schatzie.adilger.int>
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Andreas Dilger wrote:
> On Nov 20, 2003  15:44 -0500, Timothy Miller wrote:
> 
>>This could be a problem if COW causes you to run out of space when 
>>writing to the file.
> 
> 
> Not much different than running out of space copying a file.

It is, though.  If you run out of space copying a file, you know it when 
you're copying.  Applications don't usually expect to get out-of-space 
errors while overwriting something in the middle of a file.

In effect, your free space and your used space add up to greater than 
the capacity of the disk.  An application that checks for free space 
before doing something would be fooled into thinking there is more free 
space than there really is.  How can an application find out in advance 
that a file that it's about to modify (without appending anything to the 
end) is going to need more disk space?


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