Re: [PATCH] losetup: add option for O_DIRECT

[Karel Zak <kzak@redhat.com>]

On Tue, Aug 12, 2008 at 04:26:10PM -0500, Archie Cobbs wrote:
> On Thu, Aug 7, 2008 at 1:26 PM, Archie Cobbs <archie@dellroad.org> wrote:
> > I have an application involving the loopback device where it would be
> > valuable for the underlying file to be opened with the O_DIRECT flag.
> >
> > Any thoughts one way or the other about adding support to losetup(8)
> > and mount(8) for a 'direct' option that would enable this?
> >
> > I will propose a patch if people think this would be a reasonable thing to do.
> 
> Add support for opening loopback files with O_DIRECT.
[...]

>         mode = (*options & SETLOOP_RDONLY) ? O_RDONLY : O_RDWR;
> +       if (*options & SETLOOP_DIRECT)
> +               mode |= O_DIRECT;
>         if ((ffd = open(file, mode)) < 0) {


 Do you remember  http://lkml.org/lkml/2007/1/10/233  ?

 .. use O_DIRECT for files is BAD idea (and loop device is nothing
 other than a file on standard FS).

 I'm really not sure if we want to support this feature. I'm also not
 sure if kernel loop device code is ready for O_DIRECT. (BTW, O_DIRECT
 reads and writes must be aligned, ...)

 Sorry, but I have to see ACK/NACK from relevant kernel person.
 Redirecting to lkml.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>