From qemu-devel  Fri Mar 09 08:35:39 2012
From: Chris Wedgwood <cw () f00f ! org>
Date: Fri, 09 Mar 2012 08:35:39 +0000
To: qemu-devel
Subject: Re: [Qemu-devel] [RFC PATCH 14/17] block: support FALLOC_FL_PUNCH_HOLE trimming
Message-Id: <20120309083539.GA28349 () puku ! stupidest ! org>
X-MARC-Message: https://marc.info/?l=qemu-devel&m=133128221419365

> SEEK_HOLE could provide a very simple heuristic to detect preallocated
> files (unfortunately ext4 does not implement SEEK_HOLE yet).

SEEK_HOLE is a weird (confusing and no intuitive) API (IMO).  There is
FIEMAP or whatever it's called which seems somewhat saner.

XFS specific there is also GETBMAP[X].


Simplest still compare the blocks allocated by the file
to it's length (ie. stat.st_blocks != stat.st_size>>9).