linux-ext4 - Re: ext4 df free space reporting not reliable?

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Message-ID: <20100613185858.GB8055@thunk.org>
Date:	Sun, 13 Jun 2010 14:58:59 -0400
From:	tytso@....edu
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: ext4 df free space reporting not reliable?

On Sun, Jun 13, 2010 at 12:34:51PM +0200, Andi Kleen wrote:
> > Are you creating the files as root?  Sounds like the standard reserved
> > blocks behavior that's been around since ext3, ext2, BSD's ufs, etc...
> 
> Yes everything is root.
> 
> I would expect root df to not report the reservation. Is that not the case?

No, the reservation is always reported, regardless of which user ID is
executing the statfs(2) system call.  This has always been true, going
all the way back to BSD 4.3.

I could see the argument for doing this differently, but I could also
see that being very surprising for people to see different results
depending on whether they are running df from a setuid shell or not.
I'm not aware of any Unix system which has implemented the root-only
reservation system which has done this.

	    	    	   	     	  - Ted
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