Re: [PATCH] Qemu support for PPC

From: Rusty Russell (rusty@rustcorp.com.au)
Date: Mon Apr 07 2003 - 20:52:57 EST


In message <20030407134954.A31558@infradead.org> you write:
> On Mon, Apr 07, 2003 at 06:34:17PM +1000, Rusty Russell wrote:
> > Oh good: a serious question. Why don't we drop the personality field
> > in struct task_struct and just use exec_domain? Then the flags could
> > be unfolded from the personality number, and placed in a "flags"
> > element in struct exec_domain, the personality() macro would vanish,
> > the set_personality() macro would vanish, and things would be
> > generally clearer?
>
> The personality number is exposed through sys_personality, so unfortunately
> we can't get rid of it. I still wonder what crack the person inviting this
> scheme was smoking, though..

Yes. It's a PITA that the bottom 8 bits map to exec_domain, and the
rest are random flags. If each different personality mapped to a
separate exec_domain, the flags could be moved to the exec_domain
struct and it'd be far more logical. But as you say, this would break
userspace which expects to be able to set the exec_domain and the
flags separately 8(.

BTW, there's a module refcount leak here:

int
__set_personality(u_long personality)
{
        struct exec_domain *ep, *oep;

        ep = lookup_exec_domain(personality);
        if (ep == current_thread_info()->exec_domain) {
                current->personality = personality;
                return 0;
        }

You need "module_put(ep->owner)", since lookup_exec_domain bumps the
refcount.

> > That applies to any kernel mod, of course. qemu is much more usable
> > (ie. it's sanely packagable) with this functionality, ie. it's pretty
> > much a requirement for increasing adoption.
>
> You can just easily let it run in a chroot or separate namespace,
> you just won't get second look semantics. (Personally I think that's
> a benefit, but some people disagree with this).

No, then you can't access your files, which is unacceptable for many
users.

I've done the userspace implementation: I'll see if Fabrice chokes on
the speed hit.

Cheers,
Rusty.

--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
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