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

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Message-ID: <CAHk-=wgA=rB=7M_Fe3n9UkoW_7dqdUT2D=yb94=6GiGXEuAHDA@mail.gmail.com>
Date:   Fri, 10 Feb 2023 12:27:01 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Dave Chinner <david@...morbit.com>,
        Matthew Wilcox <willy@...radead.org>,
        Stefan Metzmacher <metze@...ba.org>,
        Jens Axboe <axboe@...nel.dk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux API Mailing List <linux-api@...r.kernel.org>,
        io-uring <io-uring@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Samba Technical <samba-technical@...ts.samba.org>
Subject: Re: copy on write for splice() from file to pipe?

On Fri, Feb 10, 2023 at 11:56 AM Andy Lutomirski <luto@...nel.org> wrote:
>
> i think this is almost exactly what Jeremy and Stefan are asking for
> re: notification when the system is done with a zero-copy send:

Yeah, right now it's all just "incremented page counts", I think.

Even the pipe code itself doesn't know about writes that have already
been done, but that are pending elsewhere.

You'd have to ask the target file descriptor itself about "how much do
you have pending" or something.

           Linus