On Mon, Jan 09, 2012 at 11:27:30AM +0100, Hannes Reinecke wrote: > Quite a lot of discussion has come up recently on supporting Copy > Offload (aka SCSI XCOPY) with linux. > > During the course of this several topics were found which need some > discussion: > > - Interface: do we need a new syscall? Should we try to resurrect > the original sys_copyfile() approach from Joel Becker? > What are the areas and use-cases this syscall should cover? > > - Scope: SCSI XCOPY is not the only possible user here, CIFS and > NFSv4 have similar needs. We should aim for integrating all of > these use-cases. However, we need to revisit them to figure out > if and to what extend they are really compatible. > > - Implementation: The new interface is likely to reside on the > filesystem level. To quote Dave Chinner: > > e.g. for an array offload, we have to flush the source file > > page cache first so that the data being copied is known to > > be on disk, then invalidate the destination page cache if > > overwriting or extend and pre-allocate blocks if not. Then > > we have to map both files and hand that off to the array. > > > > Then there's a whole bunch of tricky questions about what > > the state of the destination file should look like while > > the copy is in progress, whether the source file should be > > allowed to change (e.g. it can't be truncated and have > > blocks freed and then reused by other files half way through > > the copy offload operation), and so on. > > - Backends: Should we concentrate on the new 'XCOPY LITE' proposal > or should we try to implement the original XCOPY command, too? > > I guess this'll warrant a joint session, as at least filesystem and > storage people will be involved here. I'll join in for sure. I've owed code for over a year now (hanging head in shame). Joel -- "Lately I've been talking in my sleep. Can't imagine what I'd have to say. Except my world will be right When love comes back my way." http://www.jlbec.org/ jlbec@xxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
