linux-kernel - Re: [PATCH 03/11] cifs: Implement splice_read to pass down ITER_BVEC not ITER

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Date:   Mon, 6 Feb 2023 07:48:08 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Steve French <smfrench@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Shyam Prasad N <nspmangalore@...il.com>,
        Rohith Surabattula <rohiths.msft@...il.com>,
        Tom Talpey <tom@...pey.com>,
        Stefan Metzmacher <metze@...ba.org>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jeff Layton <jlayton@...nel.org>, linux-cifs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Steve French <sfrench@...ba.org>
Subject: Re: [PATCH 03/11] cifs: Implement splice_read to pass down ITER_BVEC
 not ITER_PIPE

On Fri, Feb 03, 2023 at 08:59:21PM +0000, David Howells wrote:
> Provide cifs_splice_read() to use a bvec rather than an pipe iterator as
> the latter cannot so easily be split and advanced, which is necessary to
> pass an iterator down to the bottom levels.  Upstream cifs gets around this
> problem by using iov_iter_get_pages() to prefill the pipe and then passing
> the list of pages down.

Just as last time:  if cifs has a problem with splitting these iters
so does everyone else.  What about solving the root cause here?

If the splice isn't actually a splice you might as well not implement
it.