Hi,
> On Tue, 22 Feb 2022, NeilBrown wrote:
> > 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.
>
> Actually, that might be a little bit simplistic...
>
> How are you exporting the btfs filesystem on the server.
> If you are exporting each subvolume separately, then they probably look
> like different filesystems to NFS. If you export just the top level and
> allow the subvolumes to be accessed by name, then they should have the
> same superblock and reflink should work.
>
> NeilBrown
struct vfsmount {
struct dentry *mnt_root; /* root of the mounted tree */
struct super_block *mnt_sb; /* pointer to superblock */
int mnt_flags;
struct user_namespace *mnt_userns;
} __randomize_layout;
for local mount of btrfs different subvols, there are 1 same attr and 2
different attr.
same attr:
struct super_block *mnt_sb
different:
struct dentry *mnt_root;
subvol attr; to save it in struct user_namespace?
for nfs mount of btrfs different subvols, there maybe similar way?
Best Regards
Wang Yugui (wangyugui@xxxxxxxxxxxx)
2022/02/22
