Re: [RFC v1 01/19] fs: Don't copy beyond the end of the file

["bfields@fieldses.org" <bfields@fieldses.org>]

On Thu, Mar 09, 2017 at 07:35:59AM -0800, hch@infradead.org wrote:
> On Thu, Mar 09, 2017 at 10:29:48AM -0500, bfields@fieldses.org wrote:
> > So I don't understand why it needed to be added to copy_file_range().
> > The copy and clone semantics are different enough that I think callers
> > want to know which they're getting.
> 
> Because if a file systems implements clone is literally is always better
> than doing a copy loop, so using it is an absolute non-brainer.

I guess I'm just hung up on the EINVAL vs. short copy behavior.  It
seems more annoying and error-prone to be prepared for both, as opposed
to trying clone and then explicitly falling back to copy if that doesn't
work.  Maybe it's not that big a deal.

> They do, and the system call has been in the tree for almost a year and
> a half, so we can't simply change it.  Fortunately we do have a flags
> argument that can be used to implement your preferred semantics if you
> care deeply enough about them.

Yeah.

There are also some other offset, length combinations that currently
return -EINVAL, I wonder if any of those could be repurposed e.g. for a
"keep copying to end of file" call.

--b.