+CC XFS,NFS,CIFS On Sun, Apr 12, 2020 at 1:06 PM Keno Fischer <keno@xxxxxxxxxxxxxxxxxx> wrote: > > Hello, > > I was curious about the reasoning behind the > same-mountpoint restriction in the FICLONE > ioctl. I saw that in commit > > [913b86e92] vfs: allow vfs_clone_file_range() across mount points > > this check was moved from the vfs layer into > the ioctl itself, so it appears to be a policy restriction > rather than a technical limitation. I understand why > hardlinks are disallowed across mount point boundaries, > but it seems like that rationale would not apply to clones, > since modifying the clone would not affect the original > file. Is there some other reason that the ioctl enforces > this restriction? > I don't know. I suppose that when FICLONE was introduced there wasn't any use case for cross mount clone. Note that copy_file_range() also had this restriction, which was recently lifted, because NFSv4 and CIFS needed this functionality. As far as I can tell, CIFS and NFSv4 can also support cross mount clone, but nobody stepped up to request or implement that. The question is: do you *really* need cross mount clone? Can you use copy_file_range() instead? It attempts to do remap_file_range() (clone) before falling back to kernel copy_file_range(). > Removing this restrictions would have some performance > advantages for us, but I figured there must be a good reason > why it's there that I just don't know about, so I figured I'd ask. > You did not specify your use case. Across which filesystems mounts are you trying to clone? Thanks, Amir.
