linux-kernel - Re: [take12 0/3] kevent: Generic event handling mechanism.

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Message-ID: <20060823102037.GA23664@2ka.mipt.ru>
Date:	Wed, 23 Aug 2006 14:20:37 +0400
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Jari Sundell <sundell.software@...il.com>
Cc:	David Miller <davem@...emloft.net>, kuznet@....inr.ac.ru,
	nmiell@...cast.net, linux-kernel@...r.kernel.org,
	drepper@...hat.com, akpm@...l.org, netdev@...r.kernel.org,
	zach.brown@...cle.com, hch@...radead.org
Subject: Re: [take12 0/3] kevent: Generic event handling mechanism.

On Wed, Aug 23, 2006 at 11:49:22AM +0200, Jari Sundell (sundell.software@...il.com) wrote:
> >> Only void * I'm seeing belongs to the user, (udata) perhaps you are
> >> talking of something different?
> >
> >Yes, exactly about it.
> >
> >I put union {
> >        u32 a[2];
> >        void *b;
> >}
> >epcially to eliminate that problem.
> 
> It's just random data of a known maximum size appended to the struct,
> I'm sure you can find a clean way to handle it. If you mangle the
> first variable name in your union, you'll end up with something that
> should be usable instead of udata.

If there will be usual pointer, size of the whole structure will be
different in kernel and userspace.

> >And I'm not that sure aboit stuff like uptr_t or how they call pointers
> >in userspace and kernelspace.
> 
> Well, I can't find any use of pointers in your struct ukevent, nor in
> any of the kqueue events in my man page. So if this is a deficit it
> applies to both, I guess?

No, it will change sizes of the structure in kernelspace and userspace,
so they just can not communicate.

> >ukevent is aligned to 8 bytes already (it's size selected to be 40 bytes),
> >so it should not be a problem.
> >
> >> Eric
> 
> Even if it is so, wouldn't it be better to be explicit about it?

Ok, I will add a comment about it.

> Rakshasa

-- 
	Evgeniy Polyakov
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