Re: [RFC][PATCH 0/5] Fiemap, an extent mapping ioctl

[Joel Becker <Joel.Becker@oracle.com>]

On Tue, May 27, 2008 at 11:56:22AM -0700, Mark Fasheh wrote:
> > > If the request has the FIEMAP_FLAG_NUM_EXTENTS flag set, then calling
> > > this helper is not necessary and fi_extents_mapped can be set
> > > directly.
> > 
> > Sounds like the count number of extents request should be a separate
> > ioctl and separate filesystem entry point instead of overloading FIEMAP.
> > 
> > Just define a simple FIECOUNT ioctl.
> 
> What about the back-end though? This is pretty transparently handled in
> fiemap_fill_next_extent() and many file systems (Ocfs2 included) would just
> have ->fiecount callbacks that are nearly identical ->fiecount to their
> ->fiemap...

	Provide generic_fiemap_fiecount() that does the operation in
terms of ->fiemap().  Then filesystems like ocfs2 can just do .fiecount
= generic_fiemap_fiecount.
	I agree with Christoph that it seems a bit overloaded when done
as a special case of FIEMAP.

Joel

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Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker@oracle.com
Phone: (650) 506-8127