linux-kernel - Re: [PATCH v20 09/32] tty, proc, kernfs, random: Use direct_splice

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Message-ID: <ZGcvfLWAqmOLrnLj@infradead.org>
Date:   Fri, 19 May 2023 01:12:44 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Hillf Danton <hdanton@...a.com>,
        Christian Brauner <brauner@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Christoph Hellwig <hch@....de>,
        John Hubbard <jhubbard@...dia.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v20 09/32] tty, proc, kernfs, random: Use
 direct_splice_read()

On Fri, May 19, 2023 at 08:40:24AM +0100, David Howells wrote:
>  	.fasync = random_fasync,
>  	.llseek = noop_llseek,
> -	.splice_read = generic_file_splice_read,
> +	.splice_read = direct_splice_read,

Pinging Al (and maybe Linus): is there any good reason to not simply
default to direct_splice_read if ->read_iter is implemented and
->splice_read is not once you remove ITER_PIPE?  As long as we
assure direct_splice_read is simply a ->read_iter into newly
allocated pages I can't think of anything that would go wrong there.