On 2013-02-21, at 7:57 AM, Ric Wheeler wrote: > On 02/21/2013 02:51 PM, Myklebust, Trond wrote: >> On Thu, 2013-02-21 at 12:37 +0100, Ric Wheeler wrote: >>> We have debated the need to have a system call to allow for offloading copy >>> operations, for example to an NFS server (part to the new NFS 4.2 >>> specification), SCSI target device (two different SCSI commands do this), local >>> file systems (reflink, etc) and I suspect many other possible parts of the stack >>> could implement this. >> sendfile64() pretty much already has the right arguments for a >> "copyfile", however it would be nice to add a 'flags' parameter: the >> NFSv4.2 version would use that to specify whether or not to copy file >> metadata. > > That would seem to be enough to me and has the advantage that it is an relatively obvious extension to something that is at least not totally unknown to developers. > > Do we need more than that for non-NFS paths I wonder? What does reflink need or the SCSI mechanism? IMHO, the critical part about a copy syscall is avoiding the data copy to/from userspace. Copying file attributes opens up a huge morass of issues related to which attrs/xattrs/ACLs are copied, yet those don't cost nearly so much as the data copies. We definitely want the API to be flexible enough to do server-side copies (e.g. NFS and CIFS), but we also need to allow data copies for regular files between different local and/or network filesystems within the VFS. Cheers, Andreas >>> The earliest discussion of such a system call I saw happened back in 2001, I >>> know we had another more recent flurry (2-3 years back?) as well that got >>> tangled up and died away. >>> >>> Given the new popularity of this in storage devices and the use case for virt >>> guests, any chance to get a proposal floated this year that might be able to >>> land upstream in our life times :) ? >> I'm planning on soon dusting off the NFS prototype that NetApp wrote 3 >> years ago and converting at least the client implementation into >> something that can go upstream. We do also have a server prototype for >> Linux, but the copy offload between 2 different servers is a hack and >> would need significant work. >> > > That would be really interesting, thanks! > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
