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RE: [Dazuko-devel] __d_path export and SMP safeness

From: Tikka, Sami
Subject: RE: [Dazuko-devel] __d_path export and SMP safeness
Date: Fri, 9 Sep 2005 15:41:01 +0300

Because dazuko is an LKM (loadable kernel module), it only has access to
exported kernel symbols. If dazuko was built into the kernel during
compilation, like the proc filesystem, then dazuko would have access to the
same information as the proc filesystem and there would be no problem to
begin with.

But there are other problems in building dazuko into the kernel: Dazuko would
have to be included into the standard Linus kernel tree and distribution
vendors would have to be convinced to turn dazuko on in their kernels.

Providing dazuko as a kernel patch would be another approach but it would
require end users to compile their own kernels and that is so 1990s, not to
mention the extra effort in testing, deployment and upgrading.

There is a way to get the address of the __d_path function even if it is not

a) You can search for it, just like dazuko searches for sys_call_table in
Linux 2.4 if sys_call_table is not exported.

b) User or some script can look up the __d_path address from System.map file
and pass it in as a module command line parameter or pass it to the driver
using the API.

Approach a) might fail sometimes and approach b) requires extra steps to load
the module, steps that someone might forget to do. Also, System.map file
might be unavailable (although many, if not most, vendors provide it with
their kernels.)

-- Sami

>-----Original Message-----
>From: Tushar [mailto:address@hidden 
>Sent: Friday, September 09, 2005 2:19 PM
>To: Tikka, Sami
>Cc: address@hidden
>Subject: RE: [Dazuko-devel] __d_path export and SMP safeness
>As /proc is dynamically generated, it would be great if 
>somehow we can manage to get the root entry in kernel space 
>itself and return final path to user. This way, we can keep 
>semantics of filename field same for all process. Please let 
>me know what u people think about this.

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