linux-kernel - Re: [RFC PATCH 1/4] splice: Fix corruption of spliced data after splice() returns

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Message-ID: <CAJfpegstr2CwC2ZL4-y_bAjS3hqF_vta5e4XQneJYmxz9rhVpA@mail.gmail.com>
Date:   Mon, 24 Jul 2023 15:55:21 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     David Howells <dhowells@...hat.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Matt Whitlock <kernel@...twhitlock.name>,
        netdev@...r.kernel.org, Dave Chinner <david@...morbit.com>,
        Jens Axboe <axboe@...nel.dk>, linux-fsdevel@...ck.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@....de>, linux-fsdevel@...r.kernel.org
Subject: Re: [RFC PATCH 1/4] splice: Fix corruption of spliced data after
 splice() returns

On Mon, 24 Jul 2023 at 11:44, David Howells <dhowells@...hat.com> wrote:
>
> Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>
> > > So what's the API that provides the semantics of _copying_?
> >
> > It's called "read()" and "write()".
>
> What about copy_file_range()?  That seems to fall back to splicing if not
> directly implemented by the filesystem.  It looks like the manpage for that
> needs updating too - or should that actually copy?

Both source and destination of copy_file_range() are regular files and
do_splice_direct() is basically equivalent to write(dest, mmap of
source), no refd buffers remain beyond the end of the syscall.  What
is it that should be updated in the manpage?

Thanks,
Miklos