On Thu, 17 Feb 2022, Wang Yugui wrote: > Hi, > > > On Thu, 17 Feb 2022, Wang Yugui wrote: > > > Hi, > > > Cc: NeilBrown > > > > > > btrfs cross-vfsmount reflink works well now with these 2 patches. > > > > > > [PATCH] fs: allow cross-vfsmount reflink/dedupe > > > [PATCH] btrfs: remove the cross file system checks from remap > > > > > > But nfs over btrfs still fail to do cross-vfsmount reflink. > > > need some patch for nfs too? > > > > NFS doesn't support reflinks at all, does it? > > NFS support reflinks now. > > # df -h /ssd > Filesystem Type Size Used Avail Use% Mounted on > T640:/ssd nfs4 17T 5.5T 12T 34% /ssd > # /bin/cp --reflink=always /ssd/1.txt /ssd/2.txt > # uname -a > Linux T7610 5.15.24-3.el7.x86_64 #1 SMP Thu Feb 17 12:13:25 CST 2022 x86_64 x86_64 x86_64 GNU/Linux > So it does ..... ahhh, the CLONE command in NFSv4.2..... This is used by the .remap_file_range file operation. That operation only gets called when the "from" and "to" files have the same superblock. btrfs has an .... interesting concept of filesystem identity. While different "subvols" have the same superblock locally, when they are exported over NFS they appear to be different filesystems and so have different superblocks. This is in part because btrfs cannot create properly unique inode numbers across the whole filesystem. Until btrfs sorts itself out, it will not be able to work with NFS properly. NeilBrown
