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. 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. - z -- 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