linux-kernel - Re: [PATCH 1/1] UML: fix missing non-blocking I/O, now DEBUG

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Date:	Mon, 11 Jun 2007 17:16:04 -0400
From:	Jeff Dike <jdike@...toit.com>
To:	Eduard-Gabriel Munteanu <maxdamage@...din.ro>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] UML: fix missing non-blocking I/O, now DEBUG_SHIRQ works

On Mon, Jun 11, 2007 at 10:39:56PM +0300, Eduard-Gabriel Munteanu wrote:
> No offense, but this is an ugly hack. 

I'm not going to defend it too much, but the alternatives don't seem any
better to me.

> What if sizeof(int) !=  sizeof(long)?

Doesn't matter - the casting will preserve the value.  Of greater
concern is the relationship between sizeof(void *) and sizeof(long).
That's not guaranteed by the standard, but is by gcc.

> You're calling glibc functions
> with that fd as a parameter. On some arches, compiling will issue
> warnings or simply fail. 

Which ones?

> An alternative would be to use kmalloc instead of a global static 
> variable. Do you like this one more?

No, that trades the global variable for a new point of failure.

The main reason I like the current casting better than your global
(not by a lot) is that globals have to be audited for SMP safety.  So,
I don't want any globals which don't need to be.  This implies a
local, and to minimize the machinery associated with that (kmalloc, or
passing a pointer and synchronizing to avoid returning too soon), just
passing the descriptor in the pointer and accepting the casting needed
to get it through the compiler.

				Jeff

-- 
Work email - jdike at linux dot intel dot com
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