[Ocfs2-devel] [PATCH 1/3] fs: Document the reflink(2) system call.

[Joel Becker]

On Tue, May 05, 2009 at 02:01:36PM +0100, Jamie Lokier wrote:
> Joel Becker wrote:
> > 	Here's another fun trick.  Overwriting rsync, instead of copying
> > blocks from the already-existing source could reflink the source to the
> > .temporary, then only write the changed blocks.  And since you own both
> > files, it just works.  If you're overwriting someone else's file?  The
> > old copy behavior is fine.
> 
> The moment rsync overwrites a single block, the whole reflink file
> will be copied by the filesystem, and then rsync will overwrite other
> blocks in the copy.

	This is not cowlink.  It's not a "CoW the whole thing when I
touch one block".  It's a new file (new inode for most implementations)
that just shares the data extents.  So if I write to one block, I only
need to CoW that one block.
	See my other email with the wiki pages.

Joel

-- 

"Maybe the time has drawn the faces I recall.
 But things in this life change very slowly,
 If they ever change at all."

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