On Fri, Apr 27, 2018 at 01:45:40PM -0600, Andreas Dilger wrote: > On Apr 27, 2018, at 12:25 PM, Steve French <smfrench@xxxxxxxxx> wrote: > > > > Are there any user space tools (other than our test tools and xfs_io > > etc.) that support copy_file_range? Looks like at least cp and rsync > > and dd don't. That syscall which now has been around a couple years, > > and was reminded about at the LSF/MM summit a few days ago, presumably > > is the 'best' way to copy a file fast since it tries all the > > mechanisms (reflink etc.) in order. > > > > Since copy_file_range syscall can be 100x or more faster for network > > file systems than the alternative, was surprised when I noticed that > > cp and rsync didn't support it. It doesn't look like rsync even > > supports reflink either(although presumably if you call > > copy_file_range you don't have to worry about that), and reads/writes > > are 8K. See copy_file() in rsync/util.c > > > > In the cp command it looks like it can call the FICLONE IOCTL (see > > clone_file() in coreutils/src/copy.c) but doesn't call the expected > > "copy_file_range" syscall. > > > > In the dd command it doesn't call either - see dd_copy in corutils/src/dd.c > > > > Since it can be 100x or more faster in some cases to call > > copy_file_range than do reads/writes back and forth to do a copy > > (especially if network or clustered backend or cloud), what tools are > > the best to recommend? > > > > Would rsync or cp be likely to take patches to call the standard > > "copy_file_range" syscall > > (http://man7.org/linux/man-pages/man2/copy_file_range.2.html)? > > Presumably not if it has been two+ years ... but would be interested > > what copy tools to recommend to use instead. > > I would start with submitting a patch to coreutils, if you can figure > out that code enough to do so (I find it quite opaque). Since it has > been in the kernel for a while already, it should be acceptable to the > upstream coreutils maintainers to use this interface. Doubly so if you > include some benchmarks with CIFS/NFS clients avoiding network overhead > during the copy. > For cp (coreutils), apparently there was a concern that copy_file_range() expands holes; see the thread at https://lists.gnu.org/archive/html/bug-coreutils/2016-09/msg00020.html. Though, I'd think it could just be used on non-holes only. And I don't think the size_t type of 'len' is a problem either, since it's the copy length, not the file size. You just call it multiple times if the file is larger. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-cifs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
