linux-kernel - Re: [RFC PATCH 04/14] pipe: Add O_NOTIFICATION

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Message-ID: <CALCETrUka9KaOKFbNKUXcA6XvoFxiXPftctSHtN4DL35Cay61w@mail.gmail.com>
Date:   Thu, 7 Nov 2019 10:16:13 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>, raven@...maw.net,
        Christian Brauner <christian@...uner.io>,
        keyrings@...r.kernel.org, USB list <linux-usb@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 04/14] pipe: Add O_NOTIFICATION_PIPE [ver #2]

On Thu, Nov 7, 2019 at 5:39 AM David Howells <dhowells@...hat.com> wrote:
>
> Add an O_NOTIFICATION_PIPE flag that can be passed to pipe2() to indicate
> that the pipe being created is going to be used for notifications.  This
> suppresses the use of splice(), vmsplice(), tee() and sendfile() on the
> pipe as calling iov_iter_revert() on a pipe when a kernel notification
> message has been inserted into the middle of a multi-buffer splice will be
> messy.

How messy?  And is there some way to make it impossible for this to
happen?  Adding a new flag to pipe2() to avoid messy kernel code seems
like a poor tradeoff.