Re: + loop-preallocate-eight-loop-devices.patch added to -mm tree

["Ken Chen" <kenchen@google.com>]

On 5/21/07, Al Viro <viro@ftp.linux.org.uk> wrote:
> On Mon, May 21, 2007 at 03:00:55PM -0700, akpm@linux-foundation.org wrote:
> > +     if (register_blkdev(LOOP_MAJOR, "loop"))
> > +             return -EIO;
> > +     blk_register_region(MKDEV(LOOP_MAJOR, 0), range,
> > +                               THIS_MODULE, loop_probe, NULL, NULL);
> > +
> > +     for (i = 0; i < nr; i++) {
> > +             if (!loop_init_one(i))
> > +                     goto err;
> > +     }
> > +
> > +     printk(KERN_INFO "loop: module loaded\n");
> > +     return 0;
> > +err:
> > +     loop_exit();
>
> This isn't good.  You *can't* fail once a single disk has been registered.
> Anyone could've opened it by now.
>
> IOW, you need to
>         * register region *after* you are past the point of no return

That option is a lot harder than I thought.  This requires an array to
keep intermediate result of preallocated "lo" device, blk_queue, and
disk structure before calling add_disk() or register region.  And this
array could be potentially 1 million entries.  Maybe I will use
vmalloc for it, but seems rather sick.