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

From: John Ogness
Subject: Re: [Dazuko-devel] __d_path export and SMP safeness
Date: Tue, 06 Sep 2005 16:45:47 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.8) Gecko/20050718 Debian/1.7.8-1sarge1

Tikka, Sami wrote:
> Dazuko could use the exported d_path. Then the filename the driver reports
> will be relative to the current root of the process that made the file
> access. But this is not a problem. The process which gets the dazuko events
> can easily check readlink /proc/PID/root and prepend that to the filename in
> the event.
> What do you think, John? Could you make dazuko use d_path on Linux?

Well, this would double the amount of user/kernel switches, which would be a
performance hit. It would also require that the /proc system is available.

But yes, this would work.

If I were to implement this for Linux 2.6 SMP (the only affected kernels),
then I would change Dazuko to send a filename without the beginning "/" for
files in chroot'd environments. This would signal the user application that
it needed to do a lookup for the full path. This would reduce the extra
overhead to *only* file accesses in a chroot environment.

With DazukoFS we won't have this problem because we won't need __d_path().
But we can use this hack until DazukoFS is available.

This hack would only be required for Linux 2.6 SMP kernels that do not
export __d_path().

John Ogness

Dazuko Maintainer

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