I think it would not matter which ioctl is used if the target file is not opened with flag O_RDWR. Perhaps cifs.ko can make the decision to change O_WRONLY to O_RDWR based on the flag and location of the source and destination files. On Thu, Oct 17, 2013 at 5:45 AM, David Disseldorp <ddiss@xxxxxxx> wrote: > 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 -- 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
