linux-kernel - Re: [GIT PULL] General notification queue and key notifications

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Date:   Sat, 13 Jun 2020 14:04:52 +0100
From:   David Howells <dhowells@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     dhowells@...hat.com, Karel Zak <kzak@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>, dray@...hat.com,
        Miklos Szeredi <mszeredi@...hat.com>,
        Steven Whitehouse <swhiteho@...hat.com>,
        Jeff Layton <jlayton@...hat.com>, Ian Kent <raven@...maw.net>,
        andres@...razel.de,
        Christian Brauner <christian.brauner@...ntu.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        keyrings@...r.kernel.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] General notification queue and key notifications

Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> I'm not even convinced O_NOTIFICATION_PIPE is necessary, but at worst
> it will be a useful marker. I think the only real reason for it was to
> avoid any clashes with splice(), which has more complex use of the
> pipe buffers.

The main reason is to prevent splice because the iov_iter rewind for splice
gets quite tricky if the kernel can randomly insert packets into the pipe
buffer in between what splice is inserting.

> I'm so far just reading this thread and the arguments for users, and I
> haven't yet looked at all the actual details in the pull request - but
> last time I had objections to things it wasn't the code, it was the
> lack of any use.

Would you be willing at this point to consider pulling the mount notifications
and fsinfo() which helps support that?  I could whip up pull reqs for those
two pieces - or do you want to see more concrete patches that use it?

David