Re: RFC: Does ZFS block cloning do this?

Rick Macklem <rick.macklem@gmail.com> writes:
> NFSv4.2 has a CLONE operation. It is described as doing:
>    The CLONE operation is used to clone file content from a source file
>    specified by the SAVED_FH value into a destination file specified by
>    CURRENT_FH without actually copying the data, e.g., by using a
>    copy-on-write mechanism.
> [...]
> Does ZFS block cloning do this?

The question you should be asking is “does FreeBSD currently provide
something that could be used to implement this” and the answer is
VOP_COPY_FILE_RANGE(9).  It will copy the data if the underlying
filesystem does not provide a no-copy mechanism or if that mechanism
can't be used (e.g. the files are in different pools), but it shouldn't
be difficult to add a flag; calling VOP_COPY_FILE_RANGE() with that flag
would implement intra-server CLONE, and calling it without the flag
would implement intra-server COPY.

Note that VOP_COPY_FILE_RANGE() does not always copy the entire file in
a single operation; you will have to call it in a loop until len is zero
or an error occurs.

DES
-- 
Dag-Erling Smørgrav - des@FreeBSD.org