Re: [PATCH v3 3/4] vfs: allow vfs_copy_file_range() across file systems

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Fri, Sep 23, 2016 at 10:57:56AM +0300, Amir Goldstein wrote:
> On Wed, Sep 14, 2016 at 3:43 PM, Amir Goldstein <amir73il@gmail.com> wrote:
> > copy_file_range syscall returns -EXDEV if src and dest
> > file are not on the same file system.
> > The vfs_copy_file_range() helper, however, knows how to copy
> > across file systems with do_splice_direct().
> >
> > Move the enforcement of same file system from the vfs helper
> > to the syscall code.
> >
> > A following patch is going to use the vfs_copy_file_range()
> > helper in overlayfs to copy up between lower and upper
> > not on the same file system.
> >
> > Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> > ---
> >  fs/read_write.c | 16 +++++++++++-----
> >  1 file changed, 11 insertions(+), 5 deletions(-)
> >
> > diff --git a/fs/read_write.c b/fs/read_write.c
> > index 9dc6e52..6975fe8 100644
> > --- a/fs/read_write.c
> > +++ b/fs/read_write.c
> > @@ -1502,10 +1502,6 @@ 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;
> > -
> >         if (len == 0)
> >                 return 0;
> >
> > @@ -1514,7 +1510,9 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
> >                 return ret;
> >
> >         ret = -EOPNOTSUPP;
> > -       if (file_out->f_op->copy_file_range)
> > +       /* copy_file_range() method does not support cross-fs copies */
> > +       if (inode_in->i_sb == inode_out->i_sb &&
> > +           file_out->f_op->copy_file_range)
> >                 ret = file_out->f_op->copy_file_range(file_in, pos_in, file_out,
> >                                                       pos_out, len, flags);
> >         if (ret == -EOPNOTSUPP)
> > @@ -1569,6 +1567,14 @@ SYSCALL_DEFINE6(copy_file_range, int, fd_in, loff_t __user *, off_in,
> >                 pos_out = f_out.file->f_pos;
> >         }
> >
> > +       /*
> > +        * vfs_copy_file_range() can do cross-fs copy, but we want to
> > +        * fulfill the guaranty to userland that copy_file_range syscall
> > +        * does not allow cross-fs copy
> > +        */
> > +       if (file_inode(f_in.file)->i_sb != file_inode(f_out.file)->i_sb)
> > +               return -EXDEV;
> 
> Oops, that was supposed to be goto out;
> Anyway, I am holding back on the vfs_copy_file_range() patches sub set
> until I have a reliable test on xfs to fall back from clone to copy range

I could just create another error injection point that'll make XFS pretend
that it's out of space.

--D

> 
> > +
> >         ret = vfs_copy_file_range(f_in.file, pos_in, f_out.file, pos_out, len,
> >                                   flags);
> >         if (ret > 0) {
> > --
> > 2.7.4
> >
> --
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