Subject: Re: bug#6131: [PATCH]: fiemap support for efficient sparse file copy

From: Joel Becker <[email-masked]>
Date: Wed, 16 Jun 2010 02:03:42 -0700

On Wed, Jun 16, 2010 at 02:57:01PM +0800, jeff.liu wrote:
> Paul Eggert wrote:
> > For example, if a fiemap_extent has the FIEMAP_EXTENT_UNWRITTEN flag
> > set, cp should treat that as a hole, because the extent is all zeros.
> > (This will greatly help performance in some cases.)  Also, if an input
> > extent is read and a block of it is found to be zeros, cp should skip
> > over that block when writing.
> If FIEMAP_EXTENT_UNWRITTEN flag is set, we can call fallocate(2) against the dest file directly for
> the performance boost.

	Nope.  An UNWRITTEN extent is a hole, and the user asked for
holes.  If cp sees an UNWRITTEN extent it is skipped.

Joel

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Joel Becker
Principal Software Developer
Oracle
E-mail: [email-masked]
Phone: (650) 506-8127