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. Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@xxxxxxx +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg) -- 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
