From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [PATCH 0/4] Fiemap, an extent mapping ioctl - round 2
Date: Mon, 7 Jul 2008 17:53:54 +0100
Message-ID: <20080707165354.GA7707@shareable.org>
References: <20080703225124.GB29319@disturbed> <20080704121325.GB29484@shareable.org> <20080707074021.GM29319@disturbed>
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Dave Chinner wrote:
> Like:
> 
> # xfs_freeze -f <mntpt>
> # xfs_bmap -vvp <file>
> # <do something nasty with direct block access>
> # xfs_freeze -u <mntpt>

^^^ Oh, exactly the sort of thing which led to this quote from Andreas
Dilger on why FIEMAP is *not* suitable for this, on generic filesystems :-)

    "EEEEEK [...] Directly writing underneath a filesystem is major
    bad news and will likely corrupt the filesystem because [page
    cache reasons]."

Besides, if you're using the currently-XFS-specific freeze capability,
a simple fsync() before the xfs_bmap, inside the freeze, will be
sufficient won't it?

-- Jamie