On Tue, Dec 15, 2020 at 02:05:35PM +0000, Pavel Begunkov wrote:

quoted

You may find clue from the following link:

https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg2262077.html

Thanks for the link!

Al, you mentioned "Zero-length segments are not disallowed", do you have
a strong opinion on that? Apart from already diverged behaviour from the
block layer and getting in the way of this series, without it we'd also be
able to remove some extra ifs, e.g. in iterate_bvec()

I'd prefer not to support zero-length ITER_BVEC and catching them
early, as the block layer can't deal with them either.  From a quick
look at iter_file_splice_write it should be pretty trivial to fix there,
although we'll need to audit other callers as well (even if I don't
expect them to submit this degenerate case).