On Wed, 16 Oct 2013 18:36:19 -0500 Steve French <smfrench@xxxxxxxxx> wrote: > cp --reflink opens the target file for O_WRONLY before invoking the > (BTRFS) ioctl for clone file, but for copy offload over the network > the SMB2 specification requires that the target file be open O_RDWR. > > I may be able to upgrade the target file handle on the fly by > reopening it in cifs.ko, and of course I can write an SMB2/SMB3 > specific copy command, but it would be preferable to allow use of cp > --reflink since so many people are familiar with it. > > There is quite a bit of flexibility in server side copy offload - > more than cp an offer, especially when using SMB3 or later dialects > (e.g. in number of chunks sent at one time, chunk size, attributes > copied, and even whether to use T10 style offload), but still it would > be nice to support "cp --reflink" over the network. Any ideas on > this? > > After looking at copy.c in coreutils for cp - I couldn't think of any > trivial way to force cp to open the target RW. > > Ideas? You should be able to avoid this by using FSCTL_SRV_COPYCHUNK_WRITE instead of FSCTL_SRV_COPYCHUNK on the wire. The former doesn't require read access on the target, while the latter does. See [MS-SMB2] 2.2.31 and smbtorture's copy_chunk_bad_access test. Samba only supported FSCTL_SRV_COPYCHUNK until now, as that's what Windows Server 2k12 uses for copies initiated by Explorer. I've just sent out the trivial patches adding FSCTL_SRV_COPYCHUNK_WRITE support. Cheers, David -- 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
