On Fri, Oct 19, 2018 at 11:30:18AM -0400, Olga Kornievskaia wrote:
> Allow copy_file_range to copy between different superblocks but only
> of the same file system types. This feature was of interest to CIFS
> as well as NFS.
> + if (file_out->f_op->copy_file_range &&
> + (file_in->f_op->copy_file_range ==
> + file_out->f_op->copy_file_range)) {
That is seriously asking for trouble. If at some point we add
a library function usable as ->copy_file_range() instance, this
will turn into a hard-to-spot problem.
Comparing methods like that is best avoided. If you want to compare
fs types, do just that - it's not hard.
Another potential issue here is the interplay with local filesystems
using vfs_clone_file_prep_inodes() (or Darrick's series lifting that
into generic code). There we assume the same block size on both
sides; that is automatically true if they live on the same superblock,
but with your changes it's no longer true.
