Re: [Fwd: [linux-audio-dev] info point on linux hdr]

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Subject: Re: [Fwd: [linux-audio-dev] info point on linux hdr]
From: Benno Senoner (sbenno_AT_gardena.net)
Date: Sat Apr 15 2000 - 19:50:48 EEST


On Sat, 15 Apr 2000, Stephen C. Tweedie wrote:
> Hi,
>
> On Sat, Apr 15, 2000 at 12:32:50PM +0200, Benno Senoner wrote:
> > On Sat, 15 Apr 2000, Paul Barton-Davis wrote:
>
> > > >PS: Does anyone know how to make a RAW I/O device on a spare disk partition,
> > > >and then put an ext2 over it (running the whole partition in RAWIO mode) ?
> > > >Is that possible ?
>
> It's fundamentally impossible. The concepts are orthogonal.
>
> There are four separate ways of getting access to a block device driver.
> You can use a block device in /dev. You can use a raw IO device in
> /dev/raw/ if you have a kernel which supports it. You can use the swap
> code to access it as a swap partition. Or, finally, you can use the
> filesystem code to access it as a filesystem. The same device driver
> is used underneath in each case.
>
> Running ext2 over a character mode device simply doesn't make sense:
> it's the same device driver underneath, the behaviour wouldn't be
> any different.

Stephen, thanks for the explanation, it's all clear now. Sorry for my stupid
assumption.

Anyway does anyone know if implementing O_DIRECT would be a big amount
of work in kernel 2.3.x ?
Does this require a substantial rewrite of the buffer cache code and/or page
cache code, or are the most important things already in place ?

Is the O_DIRECT handling a filesystem issue or a block device driver issue.
Or more precisely: do you have to implement direct I/O for each filesystem
(ext2, FAT etc), or is it enough to change the block device driver ?

Do you know if XFS for Linux will support this (if the O_DIRECT is a filesystem
issue, otherwise ignore this question) ?

>
> --Stephen

Benno.


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