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

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Message-ID: <c3f166d3-35b6-25cf-6ccb-8650e90a5a17@samba.org>
Date:   Fri, 10 Feb 2023 20:29:57 +0100
From:   Stefan Metzmacher <metze@...ba.org>
To:     Jeremy Allison <jra@...ba.org>, 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>,
        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?

Am 10.02.23 um 19:19 schrieb Jeremy Allison:
> 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.

Yes, I guess we can use it if the file is read-only (from it's acls),
or when the client has a read lease. And of course we can have an I don't care
option, maybe reusing 'use sendfile = yes' as that has the same problem in
the existing code already.

metze