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

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Message-ID: <1845768.1684514823@warthog.procyon.org.uk>
Date:   Fri, 19 May 2023 17:47:03 +0100
From:   David Howells <dhowells@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     dhowells@...hat.com, 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>,
        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

Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> > +       if (S_ISREG(file_inode(in)->i_mode) ||
> > +           S_ISBLK(file_inode(in)->i_mode)) {
> 
> This really feels fundamentally wrong to me.
> 
> If block and regular files have this limit, they should have their own
> splice_read() function that implements that limit.
> 
> Not make everybody else check it.
> 
> IOW, this should be a separate function ("block_splice_read()" or
> whatever), not inside a generic function that other users use.

This is just an optimisation to cut down the amount of bufferage allocated, so
I could just drop it and leave it to userspace for now as the filesystem/block
layer will stop anyway if it hits the EOF.  Christoph would prefer that I call
direct_splice_read() from generic_file_splice_read() in all O_DIRECT cases, if
that's fine with you.

David