linux-kernel - Re: open(O_DIRECT) on a tmpfs?

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Message-Id: <E1H2TsG-0000h9-0Z@be1.lrz>
Date:	Thu, 04 Jan 2007 15:47:19 +0100
From:	Bodo Eggert <7eggert@....de>
To:	Michael Tokarev <mjt@....msk.ru>,
	Linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: open(O_DIRECT) on a tmpfs?

Michael Tokarev <mjt@....msk.ru> wrote:

> I wonder why open() with O_DIRECT (for example) bit set is
> disallowed on a tmpfs (again, for example) filesystem,
> returning EINVAL.
> 
> Yes, the question may seems strange a bit, because of two
> somewhat conflicting reasons.  First, there's no reason to
> use O_DIRECT with tmpfs in a first place, because tmpfs does
> not have backing store at all, so there's no place to do
> direct writes to.  But on another hand, again due to the very
> nature of tmpfs, there's no reason not to allow O_DIRECT
> open and just ignore it, -- exactly because there's no
> backing store for this filesystem.

I'm using a tmpfs as a mostly-ramdisk, that is I've set up a large swap
partition in case I need the RAM instead of using it for a filesystem.
Therefore it will sometimes have a backing store.

OTOH, ramfs does not have this property (the cache is the backing store),
so it would make sense to allow it at least there.

BTW: Maybe you could use a ramdisk instead of the loop-on-tmpfs.
-- 
Ich danke GMX dafür, die Verwendung meiner Adressen mittels per SPF
verbreiteten Lügen zu sabotieren.

http://david.woodhou.se/why-not-spf.html
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