linux-kernel - Re: copy on write for splice() from file to pipe?

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Message-ID: <Y+aKuC1PuvX4STEI@jeremy-acer>
Date:   Fri, 10 Feb 2023 10:19:36 -0800
From:   Jeremy Allison <jra@...ba.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        Linux API Mailing List <linux-api@...r.kernel.org>,
        Dave Chinner <david@...morbit.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Stefan Metzmacher <metze@...ba.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Samba Technical <samba-technical@...ts.samba.org>,
        io-uring <io-uring@...r.kernel.org>
Subject: Re: copy on write for splice() from file to pipe?

On Fri, Feb 10, 2023 at 09:57:20AM -0800, Andy Lutomirski via samba-technical wrote:
>
>(And if Samba needs to make sure that future writes don't change the
>outgoing data even two seconds later when the data has been sent but
>not acked, then maybe a fancy API could be added to help, or maybe
>Samba shouldn't be using zero copy IO in the first place!)

Samba doesn't need any of this. The simplest thing to do is
to restrict splice-based zero-copy IO to files leased by
a single client, where exclusive access to changes is controled
by the client redirector.