linux-kernel - Re: [PATCH v4 4/5] cramfs: add mmap support

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Message-ID: <20171003153659.GA31600@infradead.org>
Date:   Tue, 3 Oct 2017 08:37:00 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Richard Weinberger <richard.weinberger@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "linux-embedded@...r.kernel.org" <linux-embedded@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Chris Brandt <Chris.Brandt@...esas.com>
Subject: Re: [PATCH v4 4/5] cramfs: add mmap support

On Tue, Oct 03, 2017 at 11:30:50AM -0400, Nicolas Pitre wrote:
> Unless you have a better scheme altogether  to suggest of course, given 
> the existing constraints.

I still can't understand why this convoluted fault path that finds
vma, attempts with all kinds of races and then tries to update things
like vm_ops is even nessecary.

We have direct mappings of physical address perfectly working in the
DAX code (even with write support!) or in drivers using remap_pfn_range
so a really good explanation why neither scheme can be used is needed
first.