Re: [PATCH v5 01/12] VFS: move cross device copy_file_range() check into filesystems

[Olga Kornievskaia <olga.kornievskaia@gmail.com>]

On Mon, Oct 29, 2018 at 2:03 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
> On Mon, Oct 29, 2018 at 7:41 PM Olga Kornievskaia
> <olga.kornievskaia@gmail.com> wrote:
> >
> > From: Olga Kornievskaia <kolga@netapp.com>
> >
> > This patch makes it the responsibility of individual filesystems to
> > allow or deny cross device copies.  Both NFS and CIFS have operations
> > for cross-server copies, and later patches will implement this feature.
> >
> > Note that as of this patch, the copy_file_range() function might be passed
> > superblocks from different filesystem types. -EXDEV should be returned
> > if cross device copies aren't supported.
>
> This Note is not ok.
> As Dave commented, you shoud make this change in a separate path.
> I will explain...
>
> >
> > Reviewed-by: Amir Goldstein <amir73il@gmail.com>
> > Reviewed-by: Matthew Wilcox <willy@infradead.org>
> > Reviewed-by: Steve French <stfrench@microsoft.com>
> > Reviewed-by: Jeff Layton <jlayton@kernel.org>
> > Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
> > ---
> >  Documentation/filesystems/porting | 7 +++++++
> >  fs/cifs/cifsfs.c                  | 3 +++
> >  fs/nfs/nfs4file.c                 | 3 +++
> >  fs/overlayfs/file.c               | 3 +++
> >  fs/read_write.c                   | 7 ++-----
> >  5 files changed, 18 insertions(+), 5 deletions(-)
> >
> > diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting
> > index 7b7b845..897e1e7 100644
> > --- a/Documentation/filesystems/porting
> > +++ b/Documentation/filesystems/porting
> > @@ -622,3 +622,10 @@ in your dentry operations instead.
> >         alloc_file_clone(file, flags, ops) does not affect any caller's references.
> >         On success you get a new struct file sharing the mount/dentry with the
> >         original, on failure - ERR_PTR().
> > +--
> > +[mandatory]
> > +       ->copy_file_range() may now be passed files which belong to two
> > +       different superblocks of the same file system type or which belong
> > +       to two different filesystems types all together. As before, the
> > +       destination's copy_file_range() is the function which is called.
> > +       If it cannot copy ranges from the source, it should return -EXDEV.
> > diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
> > index 7065426..ca8fc87 100644
> > --- a/fs/cifs/cifsfs.c
> > +++ b/fs/cifs/cifsfs.c
> > @@ -1114,6 +1114,9 @@ static ssize_t cifs_copy_file_range(struct file *src_file, loff_t off,
> >         unsigned int xid = get_xid();
> >         ssize_t rc;
> >
> > +       if (file_inode(src_file)->i_sb != file_inode(dst_file)->i_sb)
> > +               return -EXDEV;
> > +
> >         rc = cifs_file_copychunk_range(xid, src_file, off, dst_file, destoff,
> >                                         len, flags);
> >         free_xid(xid);
> > diff --git a/fs/nfs/nfs4file.c b/fs/nfs/nfs4file.c
> > index 4288a6e..5a73c90 100644
> > --- a/fs/nfs/nfs4file.c
> > +++ b/fs/nfs/nfs4file.c
> > @@ -135,6 +135,9 @@ static ssize_t nfs4_copy_file_range(struct file *file_in, loff_t pos_in,
> >  {
> >         ssize_t ret;
> >
> > +       if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
> > +               return -EXDEV;
> > +
> >         if (file_inode(file_in) == file_inode(file_out))
> >                 return -EINVAL;
> >  retry:
> > diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> > index aeaefd2..0331e33 100644
> > --- a/fs/overlayfs/file.c
> > +++ b/fs/overlayfs/file.c
> > @@ -483,6 +483,9 @@ static ssize_t ovl_copy_file_range(struct file *file_in, loff_t pos_in,
> >                                    struct file *file_out, loff_t pos_out,
> >                                    size_t len, unsigned int flags)
> >  {
> > +       if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
> > +               return -EXDEV;
> > +
> >         return ovl_copyfile(file_in, pos_in, file_out, pos_out, len, flags,
> >                             OVL_COPY);
> >  }
> > diff --git a/fs/read_write.c b/fs/read_write.c
> > index 39b4a21..7a912e3 100644
> > --- a/fs/read_write.c
> > +++ b/fs/read_write.c
> > @@ -1575,10 +1575,6 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
> >             (file_out->f_flags & O_APPEND))
> >                 return -EBADF;
> >
> > -       /* this could be relaxed once a method supports cross-fs copies */
> > -       if (inode_in->i_sb != inode_out->i_sb)
> > -               return -EXDEV;
> > -
>
> IMO, series will look the least awkward, if you start with "moving"
> this check to before
>  file_in->f_op->clone_file_range() AND before file_in->f_op->copy_file_range().
> The title of the patch would be something like:
> "VFS: generic cross-device copy_file_range() support for all filesystems"
> (Dave's suggested commit message)
>
> Then, in the next patch, which is this patch you posted
> "VFS: move cross device copy_file_range() check into filesystems"
>
> You will only need to remove the same fs check from before
> file_in->f_op->copy_file_range() and add it inside filesystems.
>
> I hope that is clear.
>

You want to make the side-effect into the first class citizen. Ok.