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

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Message-ID: <nycvar.YSQ.7.76.1710031137580.5407@knanqh.ubzr>
Date:   Tue, 3 Oct 2017 11:40:28 -0400 (EDT)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Christoph Hellwig <hch@...radead.org>
cc:     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, 3 Oct 2017, Christoph Hellwig wrote:

> 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.

I provided that explanation several times by now in my cover letter. And 
separately even to you directly at least once.  What else should I do?


Nicolas