Change Details

``` First, we need to ensure that in and out lower vnodes are compatible for the call to VOP_COPY_FILE_RANGE() on lower fs, otherwise fall back to vn_generic_copy_file_range(). Second, lower vnodes need to be referenced around the calls. Noted by: mjg Tested by: pho ```

``` VFS: add VOP_GETWRITEVNODE() It is similar to VOP_GETWRITEMOUNT(), and for given vnode vp should return the lower vnode which would actually handle write to vp. ``` ``` vn_copy_file_range(): find write vnodes on which to call the VOP ``` ``` vn_copy_file_range(): provide ENOSYS fallback to vn_generic_copy_file_range() ``` ``` nullfs: do not allow bypass on copy_file_range() There must be no callers of VOP_COPY_FILE_RANGE() except vn_copy_file_range(), which does enough to find the write-vnodes where to call the VOP. ```

``` First, we need to ensure that in and out lower vnodes are compatible forVFS: add VOP_GETWRITEVNODE() the callIt is similar to VOP_COPY_FILE_RANGE() on lower fsGETWRITEMOUNT(), otherwise fall back toand for given vnode vp should vn_generic_copy_file_range()return the lower vnode which would actually handle write to vp. ``` ``` Second, lower vnodes need to be referenced aroundvn_copy_file_range(): find write vnodes on which to call the calls.VOP ``` ``` vn_copy_file_range(): provide ENOSYS fallback to vn_generic_copy_file_range() ``` ``` nullfs: do not allow bypass on copy_file_range() Noted by: mjgThere must be no callers of VOP_COPY_FILE_RANGE() except Tested by: phovn_copy_file_range(), which does enough to find the write-vnodes where to call the VOP. ```