[Sheepdog] [PATCH] sheep: unify create_and_write logic for cow and regular object

[Christoph Hellwig]

On Tue, Nov 15, 2011 at 09:31:11PM -0500, tao.peng at emc.com wrote:
> With buffer IO and delayed allocation, I agree it can see the whole
> object. But DIO... do you plan to buffer the whole object in memory
> and send it down in one write system call? With current 4MB objects,
> it seems reasonable. But how about future large objects?

The current code always reads and writes full object size chunks
in store_create_and_write_obj_cow.  If sheepdog switches to partial
object size COWs using fallocate would probably be beneficial.