linux-kernel - Re: AZFS file system proposal

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Message-ID: <20080617135722.374673b9@mercedes-benz.boeblingen.de.ibm.com>
Date:	Tue, 17 Jun 2008 13:57:22 +0200
From:	Maxim Shchetynin <maxim@...ux.vnet.ibm.com>
To:	linux-fsdevel@...r.kernel.org
Cc:	Jan Engelhardt <jengelh@...ozas.de>,
	Matthew Wilcox <matthew@....cx>, linux-kernel@...r.kernel.org
Subject: Re: AZFS file system proposal

> >> (a) What is axonram?
> >> (b) why is axonram direct_access, and my other devices (including
> >> standard PC RAM) not?
> >
> >[Axonram is a module specific for IBM CellBlade and allows access to
> >a DDR2 memory attached onto Axon controller.] You don't need
> >direct_access and not azfs for main memory because there is already
> >a pretty nice tmpfs for it.
> 
> So the reason azfs could be useful is...?

The "?" at the end of your sentence might mean a question. I would be really happy to give an answer on it if I could understand it.

> >> >+         Mounting such device with azfs gives memory mapped
> >> >access to the + underlying memory to user space.
> >> 
> >> Can't I just mmap(/dev/theblockdevice), why would I need to go through 
> >> azfs?
> >
> >Yes, you can mmap it. But what does it have to do with a file system.
> 
> Exactly, that's what I was asking myself.

I am glad I could make you feel comfortable with that answer.

> >I would say you can either mmap it or place a file system on it.
> 
> The help text implies that I *need* azfs to mmap it - and that sounds
> like a Rube Goldberg machine.

Does it? If it is really so, then only because my english is not perfect. I didn't want to compel someone to do mmap or to disturb user's rights in any other way. By the way, you can also mmap some files on AZFS like on any other file system. But mmap wouldn't work if you mount AZFS with a block size less than the system page size.

-- 
Mit freundlichen Grüßen / met vriendelijke groeten / avec regards

    Maxim V. Shchetynin
    Linux Kernel Entwicklung
    IBM Deutschland Entwicklung GmbH
    Linux für Cell, Abteilung 3250
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