Re: [PATCH] fs: try to clone files first in vfs_copy_file_range

[Christoph Hellwig <hch@lst.de>]

[fullquote removed, please get your email etiquette right or I'll stop
responding]


> For fs that support both copy and clone, I am not convinced that it up to
> VFS to take that decision for the application.

We had that discussion many times.  Yes, the system can decide it, as
the application does not see the difference.

> If application 'chose' copy over clone maybe it had a reason.

Yes, because it's lazy and simply doesn't give a f**k how the data
is copied.  Clone provides much stronger guarantees, but if you don't
need them you'll just use call that will always work.

> I suggest to move this to 'clone fallback' after copy_file_range and before
> do_splice_direct.

That won't do the right thing for the NFS case.

> A hypothetical case why copy_range implementation would be preferred
> by an application that runs over specific hypothetical fs - copy_file_range
> can be more easily implemented as a killable copy loop, returning the length
> that was copy before interrupted by a signal.

Clone is a fast metadata operation and is finished before you even
had a chance to kill it.