Re: Curious code in autostart_array

["H. Peter Anvin" <hpa@zytor.com>]

Pete Zaitcev wrote:
> Hi, guys:
> 
> My copy of 2.6.17-rc5 has the following code in autostart_array():
> 		mdp_disk_t *desc = sb->disks + i;
> 		dev_t dev = MKDEV(desc->major, desc->minor);
> 
> 		if (!dev)
> 			continue;
> 		if (dev == startdev)
> 			continue;
> 		if (MAJOR(dev) != desc->major || MINOR(dev) != desc->minor)
> 			continue;
> 
> Under what conditions do you think the last if() statement can fire?
> What is its purpose? This looks like an attempt to detect bit clipping.
> But what exactly?
> 

It can fire if either desc->major or desc->minor overflow the respective 
fields in dev_t.  Unfortunately, it's not guaranteed to do so.

	-hpa