linux-kernel - Re: [PATCH v20 03/32] splice: Make direct_read

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Message-ID: <1742093.1684485814@warthog.procyon.org.uk>
Date:   Fri, 19 May 2023 09:43:34 +0100
From:   David Howells <dhowells@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     dhowells@...hat.com, Jens Axboe <axboe@...nel.dk>,
        Al Viro <viro@...iv.linux.org.uk>,
        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,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v20 03/32] splice: Make direct_read_splice() limit to eof where appropriate

Christoph Hellwig <hch@...radead.org> wrote:

> I'm really not sure if this is a good idea.  Right now
> 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()?

> 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.

David