Re: [PATCH] [8/7] oprofile - dcookies need to use u32

From: John Levon (
Date: Wed Oct 16 2002 - 11:40:57 EST

On Tue, Oct 15, 2002 at 07:00:19PM -0700, David S. Miller wrote:

> + return (u32)dentry;
> Um, isn't this supposed to uniquely identify the dentry?
> On a platform with 64-bit pointers there's now the theoretical
> possibility of different dentries getting the same cookie ...
> That's true.
> We dealt with this (trying to use a kernel pointer as a cache held by
> userspace) in tcp_diag by making the actual object opaque. It was
> actually two u32's, and that way it worked independant of kernel
> vs. user word size.

I'm not sure that's an option :

o userspace needs to know the size of the cookie in the event buffer
o userspace would like to use the cookie as a hash value to avoid
  repeated lookups

Perhaps the best solution would be to use a separate u32 ID value,
allocated linearly. I could just refuse to allocate new dcookies in
theoretical case of overflow.

The other possibility is a dcookiefs (cat
/dev/oprofile/dcookie/34343234) but that's a lot of extra
code/complexity ...


"It's a cardboard universe ... and if you lean too hard against it, you fall
	- Philip K. Dick 
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