linux-kernel - Re: [PATCH 1/2] x86: rename PTE_MASK to PTE_PFN

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Message-Id: <200807222058.37130.rusty@rustcorp.com.au>
Date:	Tue, 22 Jul 2008 20:58:36 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86: rename PTE_MASK to PTE_PFN_MASK

On Tuesday 22 July 2008 18:36:26 Ingo Molnar wrote:
> * Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> > Rusty, in his peevish way, complained that macros defining constants
> > should have a name which somewhat accurately reflects the actual
> > purpose of the constant.
>
> Applied to tip/x86/cleanups anyway. Rusty will find out himself how bad
> this whole concept of clean and understandable code is, soon enough!

I am disgusted with this inappropriate emphasis on clarity over obscurity.  It
should be pretty clear to everyone here that we can't have both!

Fortunately, there is a way to partially rectify the situation. Ingo, please
apply.

Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
---
 include/asm-x86/page.h |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/include/asm-x86/page.h b/include/asm-x86/page.h
index 6c84622..4207518 100644
--- a/include/asm-x86/page.h
+++ b/include/asm-x86/page.h
@@ -10,6 +10,7 @@
 
 #ifdef __KERNEL__
 
+/* There's something suspicious about this line: see PTE_PFN_MASK comment. */
 #define __PHYSICAL_MASK		((phys_addr_t)(1ULL << __PHYSICAL_MASK_SHIFT) - 1)
 #define __VIRTUAL_MASK		((1UL << __VIRTUAL_MASK_SHIFT) - 1)
 
@@ -19,6 +20,7 @@
 #define PHYSICAL_PAGE_MASK	(((signed long)PAGE_MASK) & __PHYSICAL_MASK)
 
 /* PTE_PFN_MASK extracts the PFN from a (pte|pmd|pud|pgd)val_t */
+/* This line is quite subtle.  See __PHYSICAL_MASK comment above. */
 #define PTE_PFN_MASK		((pteval_t)PHYSICAL_PAGE_MASK)
 
 /* PTE_FLAGS_MASK extracts the flags from a (pte|pmd|pud|pgd)val_t */
--
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