Messages in this thread | | | Date | Fri, 22 Feb 2013 09:47:08 +0100 | From | Ric Wheeler <> | Subject | Re: New copyfile system call - discuss before LSF? |
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On 02/21/2013 11:13 PM, Myklebust, Trond wrote: > On Thu, 2013-02-21 at 23:05 +0100, Ric Wheeler wrote: >> On 02/21/2013 09:00 PM, Paolo Bonzini wrote: >>> Il 21/02/2013 15:57, Ric Wheeler ha scritto: >>>>> 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? >>> For virt we would like to be able to specify arbitrary block ranges. >>> Copying an entire file helps some copy operations like storage >>> migration. However, it is not enough to convert the guest's offloaded >>> copies to host-side offloaded copies. >>> >>> Paolo >> I don't think that the NFS protocol allows arbitrary ranges, but the SCSI >> commands are ranged based. >> >> If I remember what the windows people said at a SNIA event a few years back, >> they have a requirement that the target file be pre-allocated (at least for the >> SCSI based copy). Not clear to me where they iterate over that target file to do >> the block range copies, but I suspect it is in their kernel. > The NFSv4.2 copy offload protocol _does_ allow the copying of arbitrary > byte ranges. The main target for that functionality is indeed > virtualisation and thin provisioning of virtual machines. >
For background, here is a pointer to Fred Knight's SNIA talk on the SCSI support for offload:
https://snia.org/sites/default/files2/SDC2011/presentations/monday/FrederickKnight_Storage_Data_Movement_Offload.pdf
and a talk from Spencer Shepler that gives some detail on the NFS spec, including the "server side copy" bits:
https://snia.org/sites/default/files2/SDC2011/presentations/wednesday/SpencerShepler_IETF_NFSv4_Working_Group_v4.pdf
The talks both have references to the actual specs for the gory details.
Ric
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