Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Fri, 19 May 2023 01:47:57 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     David Howells <dhowells@redhat.com>
Cc:     Christoph Hellwig <hch@infradead.org>,
        Jens Axboe <axboe@kernel.dk>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Matthew Wilcox <willy@infradead.org>, Jan Kara <jack@suse.cz>,
        Jeff Layton <jlayton@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Logan Gunthorpe <logang@deltatee.com>,
        Hillf Danton <hdanton@sina.com>,
        Christian Brauner <brauner@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v20 03/32] splice: Make direct_read_splice() limit to eof
 where appropriate
Message-ID: <ZGc3vUU/bUpt+3Tm@infradead.org>
References: <ZGcusJQfz68H1s7S@infradead.org>
 <20230519074047.1739879-1-dhowells@redhat.com>
 <20230519074047.1739879-4-dhowells@redhat.com>
 <1742093.1684485814@warthog.procyon.org.uk>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1742093.1684485814@warthog.procyon.org.uk>
Precedence: bulk

On Fri, May 19, 2023 at 09:43:34AM +0100, David Howells wrote:
> > direct_read_splice (which also appears a little misnamed) really is
> > a splice by calling ->read_iter helper.
> 
> It can be renamed if you want a different name.  copy_splice_read() or
> copy_splice_read_iter()?

Maybe something like that, yes.

> 
> > I we don't do any of this validtion we can just call it directly from
> > splice.c instead of calling into ->splice_read for direct I/O and DAX and
> > remove a ton of boilerplate code.
> 
> There's a couple of places where we might not want to do that - at least for
> non-DAX.  shmem and f2fs for example.  f2fs calls back to buffered reading
> under some circumstances.  shmem ignores O_DIRECT and always splices from the
> pagecache.

So?  even if ->read_iter does buffered I/O for O_DIRECT it will still
work.  This can in fact happen for many other file systems due when
they fall back to buffeed I/O due to various reasons.