linux-ext4 - Re: [PATCH 01/19] mm: introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap flags

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Date:   Fri, 13 Oct 2017 11:28:40 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jan Kara <jack@...e.cz>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        linux-xfs@...r.kernel.org,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Ted Tso <tytso@....edu>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 01/19] mm: introduce MAP_SHARED_VALIDATE, a mechanism to
 safely define new mmap flags

On Fri, Oct 13, 2017 at 8:44 AM, Dan Williams <dan.j.williams@...el.com> wrote:
> On Fri, Oct 13, 2017 at 12:12 AM, Christoph Hellwig <hch@...radead.org> wrote:
>> So did we settle on the new mmap_validate vs adding a new argument
>> to ->mmap for real now?  I have to say I'd much prefer passing an
>> additional argument instead, but if higher powers rule that out
>> this version is ok.
>
> MAP_DIRECT also needs the fd now, so it would be two arguments. Before
> you say "that's bogus" I want to understand what the alternative looks
> like for notifying userspace that its get_user_pages() registration
> lease is being invalidated.
>

Jason straightened me out about how RDMA applications expect to get
notifications and now I see why the fd based scheme is lacking.