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Re: Problem with mkfs.xfs on a regular file

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: Problem with mkfs.xfs on a regular file
From: Phil White <cerise-xfs@xxxxxxxxxxxx>
Date: Thu, 28 Nov 2013 03:47:05 -0800
Cc: Eric Sandeen <sandeen@xxxxxxxxxxx>, Phil White <cerise-xfs@xxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20131128100107.GN10988@dastard>
References: <20131127023119.GB13101@boogeyman> <20131127024713.GE10988@dastard> <5296ACFB.4030901@xxxxxxxxxxx> <20131128051626.GM10988@dastard> <5296D5EB.2080008@xxxxxxxxxxx> <20131128100107.GN10988@dastard>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Nov 28, 2013 at 09:01:07PM +1100, Dave Chinner wrote:
> On Wed, Nov 27, 2013 at 11:34:35PM -0600, Eric Sandeen wrote:
> > If only we had some way to tell, programatically, whether the mkfs target
> > was a regular file or a block device, eh? ;)
> > 
> > Seriously, I always thought the requirment to specify "-d file" was silly.
> > And now I think it's even more silly, if it actually is required for
> > proper behavior...
> It has always been required if you want mkfs to create the file for
> you. And given that doing stuff like ioctl(BLKDISCARD) on files is
> completely wrong, so I think it really is needed...
> > > What mkfs needs to do is reject devices that are files when "-d
> > > file", "-l file" and "-r file" is not specified, and the problem
> > > will go away because it will catch users who forget to tell mkfs
> > > that it is supposed to be operating on an image file...
> > 
> > Or maybe just stat() it, and DTRT?
> Well, we need to stat it to make sure that it's a file if "-d file"
> is specified, and a block device if it's not. That will prevent this
> problem.  Every other xfsprogs utility has to be told that it is
> being pointed at an image file rather than a block device, so why
> should mkfs be any different?

FWIW, I have a patch to just stat() and discard LIBXFS_DIRECT if the
target is not a block device.  It worked for what I was doing and I
wouldn't mind cleaning it up if need be.

The main thing is that it seems to me that mkfs mandates that the situation
I outlined shouldn't ever fail.  That's probably something worth adding to
xfstests as well.

And writing that test, I suppose, is something I don't mind doing either.



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