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Preallocation and Ferris

To: linux-xfs@xxxxxxxxxxx
Subject: Preallocation and Ferris
From: monkeyiq <monkeyiq@xxxxxxxxxxxxxxxxxxxxx>
Date: Sat, 2 Feb 2002 22:23:15 +1000
Cc: monkeyiq@xxxxxxxxxxxxxxxxxxxxx
Sender: owner-linux-xfs@xxxxxxxxxxx
  A while back I was talking about adding preallocation support to
ferris. I didn't get around to adding it at the time, though the
doco seems much better now and I have an application which would 
be greatly enhanced using it. 

I have found the calls in xfs(5)

I am thinking of adding an interface though Ferris using both 
Ferris' support for arbitrary creation arguments 
(see http://witme.sourceforge.net/ferriscreate.paper2001/ )
and also creating a "fake" EA for preallocation-eof
which can be set to whatever size is wanted in the preallocation.
The main question I have here is how to obtain the current
amount of space that is preallocated in the file and not used.

It seems from RTFM that XFS_IOC_FSGETXATTR only tells if 
preallocation is being used. If I can tell how much space
a file has preallocated at eof then I can add a new EA and
edit it with the client shown here:

This would allow a nice interface for preallocation and make
scripting easy to be able to check for files that have been
written but are smaller than the space originally preallocated
to them.



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