Re: open(O_DIRECT) on a tmpfs?

[Bodo Eggert <7eggert@gmx.de>]

Michael Tokarev <mjt@tls.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.
-- 
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verbreiteten Lügen zu sabotieren.

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