Re: [PATCH] new system call mknod64

[Linus Torvalds]

On Mon, 21 Apr 2003, Christoph Hellwig wrote:
> 
> Not anymore for blockdevices.  And now that Al's back not anymore soon
> for charater devices, too :)

Actually, we still do it for both block _and_ character devices.

Look at "nfs*xdr.c" to see what's up.

In other words, that split is definitely not virtual. It's a real thing 
with real visibility for users.

The fact that the kernel internally has generalized it away doesn't 
matter. Any kernel virtualization of the number still _has_ to account for 
the fact that it's a real thing.

Put another way:

	0x0000000000000101

_has_ to open the same file as

	0x0000000100000001

because otherwise the kernel virtualization is broken (since they will
look the same to a user, and they will end up being written to disk the
same way).

Thus any code that only looks at 64-bit dev_t without taking this into 
account is BUGGY. 

One way to avoid the bug is to always keep all dev_t numbers in "canonical 
format". Which happens automatically if the interface is <major, minor> 
rather than a 64-bit blob.

I personally think that anything that uses "dev_t" in _any_ other way than 
<major,minor> is fundamentally broken.

		Linus