Re: bug in 2.6.22-rc2: loop mount limited to one single iso image

[Uwe Bugla <uwe.bugla@gmx.de>]

Am Sonntag, 20. Mai 2007 18:16 schrieben Sie:
> On Sun, 2007-05-20 at 09:10 -0700, Ray Lee wrote:
> > On 5/20/07, Kay Sievers <kay.sievers@vrfy.org> wrote:
> > > On 5/20/07, Ray Lee <ray-lk@madrabbit.org> wrote:
> > > > On 5/19/07, Al Viro <viro@ftp.linux.org.uk> wrote:
> > > > > On Sat, May 19, 2007 at 11:16:59PM -0700, Ray Lee wrote:
> > > > > > Ken? Ball's in your court. As the patch isn't providing a killer
> > > > > > feature for 2.6.22, I'd suggest just reverting it for now until
> > > > > > the issues are ironed out.
> > > > >
> > > > > Hold it.  The real question here is which logics do we want there.
> > > > > IOW, and how many device nodes do we want to appear and _when_ do
> > > > > we want them to appear?
> > > >
> > > > The when part is what looks to make it racy. I'm guessing that we're
> > > > relying on udev to create those loop nodes. If so, I think any scheme
> > > > that creates more on demand would give transient mount errors while
> > > > it's waiting on udev to create more nodes.
> > > >
> > > > Perhaps if we were to start with 8 loop nodes at init (as we have in
> > > > 2.6.21), and then always maintain a margin of 8 (or 4, or...) when
> > > > they start being used or detached?
> > >
> > > Until the tools can request dynamic loop device allocation from the
> > > kernel before they want to use the device, you can create as many as
> > > needed "static" loop* nodes in /lib/udev/devices/, which will be
> > > copied to /dev/ early on every bootup.
> >
> > Except that's different than current behavior presented to userspace.
> > IOW, we broke userspace for anyone using udev. Which is, y'know, a lot
> > of us.
> >
> > We're at -rc2 right now. Given that, it looks like we have two
> > options. First is to revert all this for now and try again when the
> > patch has had more testing and agreement (as this isn't a major
> > feature we're talking about here; it's effectively just a cleanup that
> > happened to have unfortunate side-effects).
> >
> > The second option is that we could have the loop device start with 8
> > nodes populated, which would match current behavior.
> >
> > A third option of requiring new userspace for 2.6.22 is a non-starter.
>
> Right, providing "preallocated" devices, 8 or the number given in
> max_loop, sounds like the best option until the tools can handle that.
>
> Thanks,
> Kay

OK people, this is what I did just to resolve the issue for now:

1. copied loop.c from 2.6.21 into the 2.6.22-rc2 tree
2. changed exactly two entries from "invalidate_bdev(bdev, 0)"

to "invalidate_bdev(bdev)"

Output is:
a. a compilable kernel
b. all four iso images are mounted as expected

Andrey's path however (i. e. copying his attached version of loop.c into the 
2.6.22-rc2 kernel tree) led to:

a. an incompilable kernel
b. endless messages trying to compile loop.c going like this (just a part of 
them - not complete anyway!):

drivers/block/loop.c:1350: error: stray '\240' in program
drivers/block/loop.c:1350: error: stray '\240' in program
drivers/block/loop.c:1350: error: stray '\240' in program
drivers/block/loop.c:1350: error: stray '\240' in program
drivers/block/loop.c:1351: error: stray '\240' in program
drivers/block/loop.c:1351: error: stray '\240' in program
drivers/block/loop.c:1351: error: stray '\240' in program
drivers/block/loop.c:1351: error: stray '\240' in program
drivers/block/loop.c:1351: error: stray '\240' in program
drivers/block/loop.c:1351: error: stray '\240' in program
drivers/block/loop.c:1351: error: stray '\240' in program
drivers/block/loop.c:1351: error: stray '\240' in program
drivers/block/loop.c:1351: error: stray '\240' in program
drivers/block/loop.c:1351: error: stray '\240' in program
drivers/block/loop.c:1351: error: stray '\240' in program
drivers/block/loop.c:1351: error: stray '\240' in program
drivers/block/loop.c:1351: error: stray '\240' in program
drivers/block/loop.c:1351: error: stray '\240' in program
drivers/block/loop.c:1351: error: stray '\240' in program
drivers/block/loop.c:1351: error: stray '\240' in program
drivers/block/loop.c: In function 'loop_register_transfer':
drivers/block/loop.c:1367: error: stray '\240' in program
drivers/block/loop.c:1367: error: stray '\240' in program
drivers/block/loop.c:1367: error: stray '\240' in program
drivers/block/loop.c:1367: error: stray '\240' in program
drivers/block/loop.c:1367: error: stray '\240' in program
drivers/block/loop.c:1367: error: stray '\240' in program
drivers/block/loop.c:1367: error: stray '\240' in program
drivers/block/loop.c:1367: error: stray '\240' in program

Thanks to Ray! Well done!

Best regards

Uwe