linux-kernel - Re: [PATCH 03/12] cifs: Implement splice_read to pass down ITER_BVEC not ITER

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Message-ID: <Y9pqke68UH9N0Qtd@infradead.org>
Date:   Wed, 1 Feb 2023 05:35:13 -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 03/12] cifs: Implement splice_read to pass down ITER_BVEC
 not ITER_PIPE

On Tue, Jan 31, 2023 at 06:28:46PM +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,

What exactly are the issues?  If cifs is running into them others will
as well, so we might better fix them in the infrastructure.

>  (1) Bulk-allocate a bunch of pages to carry as much of the requested
>      amount of data as possible, but without overrunning the available
>      slots in the pipe and add them to an ITER_BVEC.

And that basically makes the splice_read entirely pointless and you
might as well simply not support it.