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Date: Tue, 8 Jul 2008 17:36:32 +0200
From: Ed Schouten <ed@80386.nl>
To: Robert Watson <rwatson@FreeBSD.org>
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Subject: Re: Proposal: a revoke() system call
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Hello Robert,

* Robert Watson <rwatson@FreeBSD.org> wrote:
> BTW, on a similar note to the above: I've noticed there are several spots=
=20
> of relative non-atomicity in the Linux emulation code, where rather than=
=20
> just wrapping existing system calls with binary conversion of arguments=
=20
> and return values, we do a semantic wrapping that is necessarily=20
> non-atomic with respect to the native code.  For example, consider the=20
> Linuxulator open code in linux_common_open():

I also noticed similar constructs inside the stat() calls, to translate
device major/minor numbers. As you can see, some stat() routines call
translate_path_major_minor_at() after performing the regular stat()
operation. The translate_path_major_minor_at() is implemented by
calling kern_openat(). This has three disadvantages:

- It is non-atomic.

- It can only perform the translation on nodes it has O_RDONLY access
  to. This shouldn't be a big problem, but may cause inconsistencies
  when users look around in devfs.

- The translation may not always work when the calling process is out of
  file descriptors.

Yours,
--=20
 Ed Schouten <ed@80386.nl>
 WWW: http://80386.nl/

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