> -----Original Message----- > From: Zach Brown [mailto:zab@xxxxxxxxxx] > Sent: Thursday, February 21, 2013 5:25 PM > To: Myklebust, Trond > Cc: Paolo Bonzini; Ric Wheeler; Linux FS Devel; linux-kernel@xxxxxxxxxxxxxxx; > Chris L. Mason; Christoph Hellwig; Alexander Viro; Martin K. Petersen; > Hannes Reinecke; Joel Becker > Subject: Re: New copyfile system call - discuss before LSF? > > On Thu, Feb 21, 2013 at 08:50:27PM +0000, Myklebust, Trond wrote: > > On Thu, 2013-02-21 at 21:00 +0100, 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. > > > > So how would a system call based on sendfile64() plus my flag > > parameter prevent an underlying implementation from meeting your > criterion? > > If I'm guessing correctly, sendfile64()+flags would be annoying because it's > missing an out_fd_offset. The host will want to offload the guest's copies by > calling sendfile on block ranges of a guest disk image file that correspond to > the mappings of the in and out files in the guest. > > You could make it work with some locking and out_fd seeking to set the > write offset before calling sendfile64()+flags, but ugh. > > ssize_t sendfile(int out_fd, int in_fd, off_t in_offset, off_t > out_offset, size_t count, int flags); > > That seems closer. psendfile() ? I fully agree that sounds reasonable... Just being an ass. :-) > We might also want to pre-emptively offer iovs instead of offsets, because > that's the very first thing that's going to be requested after people prototype > having to iterate calling sendfile() for each contiguous copy region. vpsendfile() then? I agree that might be a little more future-proof. Particularly given that the underlying protocols tend to be fully asynchronous, and so it makes sense to queue up more than one copy at a time... Cheers, Trond -- 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
