On Thu, 2011-12-15 at 11:03 -0500, Jeff Layton wrote: > On Thu, 15 Dec 2011 10:52:13 -0500 > Chris Mason <chris.mason@xxxxxxxxxx> wrote: > > > On Thu, Dec 15, 2011 at 09:59:00AM -0500, Trond Myklebust wrote: > > > On Wed, 2011-12-14 at 17:27 -0500, J. Bruce Fields wrote: > > > > On Wed, Dec 14, 2011 at 02:42:38PM -0500, Ric Wheeler wrote: > > > > > On 12/14/2011 02:27 PM, Al Viro wrote: > > > > > >On Wed, Dec 14, 2011 at 02:22:07PM -0500, Ric Wheeler wrote: > > > > > > > > > > > >>We had an active thread a couple of years back that came out of the > > > > > >>reflink work and, at the time, there seemed to be moderately > > > > > >>positive support for adding a new system call that would fit this > > > > > >>use case (Joel Becker's copyfile()). > > > > > >> > > > > > >>Can we resurrect this effort? Is copyfile() still a good way to go, > > > > > >>or should we look at other hooks? > > > > > >copyfile(2) is probably a good way to go, provided that we do _not_ > > > > > >go baroque as it had happened the last time syscall had been discussed. > > > > > > > > > > > >IOW, to hell with progress reports, etc. - just a fastpath kind of > > > > > >thing, in the same kind of relationship to cp(1) as rename(2) is to mv(1). > > > > > >If it works - fine, if not - caller has to be ready to deal with handling > > > > > >cross-device case anyway. > > > > > > > > > > I think that this approach makes a lot of sense. Most of the > > > > > devices/targets that support the copy offload, will do it in very > > > > > reasonable amounts of time. > > > > > > > > The current NFSv4.2 draft rolls both the "fast" and "slow" cases into > > > > one operation: > > > > > > > > http://tools.ietf.org/html/draft-ietf-nfsv4-minorversion2-06#section-2 > > > > > > > > Perhaps we should ask for separate operations for the two cases. (Or at > > > > least a "please don't bother if this is going to take 8 hours" flag....) > > > > > > How would the server know? I suggest we deal with this by adding an > > > ioctl() to allow the application to poll for progress: I'm assuming now > > > that we don't expect more than 1 copyfile() system call at a time per > > > file descriptor... > > > > If we're using this to copy VM image files, I could easily imagine > > wanting to clone multiple copies of the VM in parallel. > > > > -chris > > > > Not really a problem is it? Just dup() the fd before you issue the > copyfile()? Or even simpler, just do periodic stat() on the destination > file if you want a progress report. > > Regardless, I like the simple approach that Al is suggesting here. Periodic stat() isn't good enough if you are copying subranges of a file. Part of the application here (as I understood it) is to initialise specific disk volumes on existing VM images when doing thin provisioning. In that case, the reported image size won't ever change... Cheers Trond -- Trond Myklebust Linux NFS client maintainer NetApp Trond.Myklebust@xxxxxxxxxx www.netapp.com -- 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
