linux-kernel - Re: [PATCH v1 0/7] Remove in-tree usage of MAP

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Message-ID: <20210818154217.GB24115@fieldses.org>
Date:   Wed, 18 Aug 2021 11:42:17 -0400
From:   bfields@...ldses.org (J. Bruce Fields)
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        David Laight <David.Laight@...lab.com>,
        David Hildenbrand <david@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Al Viro <viro@...iv.linux.org.uk>,
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        Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE

On Fri, Aug 13, 2021 at 05:49:19PM -0700, Andy Lutomirski wrote:
> I’ll bite.  How about we attack this in the opposite direction: remove
> the deny write mechanism entirely.

For what it's worth, Windows has open flags that allow denying read or
write opens.  They also made their way into the NFSv4 protocol, but
knfsd enforces them only against other NFSv4 clients.  Last I checked,
Samba attempted to emulate them using flock (and there's a comment to
that effect on the flock syscall in fs/locks.c).  I don't know what Wine
does.

Pavel Shilovsky posted flags adding O_DENY* flags years ago:

	https://lwn.net/Articles/581005/

I keep thinking I should look back at those some day but will probably
never get to it.

I've no idea how Windows applications use them, though I'm told it's
common.

--b.