Re: [PATCH v3 0/2] libceph: add new iov_iter msg_data type and use it for reads

[Christoph Hellwig <hch@infradead.org>]

On Fri, Jul 01, 2022 at 06:30:11AM -0400, Jeff Layton wrote:
> Currently, we take an iov_iter from the netfs layer, turn that into an
> array of pages, and then pass that to the messenger which eventually
> turns that back into an iov_iter before handing it back to the socket.
> 
> This patchset adds a new ceph_msg_data_type that uses an iov_iter
> directly instead of requiring an array of pages or bvecs. This allows
> us to avoid an extra allocation in the buffered read path, and should
> make it easier to plumb in write helpers later.
> 
> For now, this is still just a slow, stupid implementation that hands
> the socket layer a page at a time like the existing messenger does. It
> doesn't yet attempt to pass through the iov_iter directly.
> 
> I have some patches that pass the cursor's iov_iter directly to the
> socket in the receive path, but it requires some infrastructure that's
> not in mainline yet (iov_iter_scan(), for instance). It should be
> possible to something similar in the send path as well.

Btw, is there any good reason to not simply replace ceph_msg_data
with an iov_iter entirely?