linux-kernel - [RFC] Refactor kenter/kleave/kdebug macros

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Date:	Sat, 16 May 2015 20:01:33 +0300
From:	Leon Romanovsky <leon@...n.nu>
To:	dhowells@...hat.com, Linux-MM <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-cachefs@...hat.com, linux-afs@...ts.infradead.org
Subject: [RFC] Refactor kenter/kleave/kdebug macros

Dear David,

During my work on NOMMU system (mm/nommu.c), I saw definition and
usage of kenter/kleave/kdebug macros. These macros are compiled as
empty because of "#if 0" construction.
  45 #if 0
  46 #define kenter(FMT, ...) \
  47         printk(KERN_DEBUG "==> %s("FMT")\n", __func__, ##__VA_ARGS__)
  48 #define kleave(FMT, ...) \
  49         printk(KERN_DEBUG "<== %s()"FMT"\n", __func__, ##__VA_ARGS__)
  50 #define kdebug(FMT, ...) \
  51         printk(KERN_DEBUG "xxx" FMT"yyy\n", ##__VA_ARGS__)
  52 #else
  53 #define kenter(FMT, ...) \
  54         no_printk(KERN_DEBUG "==> %s("FMT")\n", __func__, ##__VA_ARGS__)
  55 #define kleave(FMT, ...) \
  56         no_printk(KERN_DEBUG "<== %s()"FMT"\n", __func__, ##__VA_ARGS__)
  57 #define kdebug(FMT, ...) \
  58         no_printk(KERN_DEBUG FMT"\n", ##__VA_ARGS__)
  59 #endif

This code was changed in 2009 [1] and similar definitions can be found
in 9 other files [2]. The protection of these definitions is slightly
different. There are places with "#if 0" protection and others with
"#if defined(__KDEBUG)" protection. __KDEBUG is supposed to be
inserted by GCC.

My question is how we should handle such duplicated debug print code?
As possible solutions, I see five options:
1. Leave it as is.
2. Move it to general include file (for example linux/printk.h) and
commonize the output to be consistent between different kdebug users.
3. Add CONFIG_*_DEBUG definition for every kdebug user.
4. Move everything to "#if 0" construction.
5. Move everything to "#if defined(__KDEBUG)" construction.

What do you think?

[1]     commit 8feae13110d60cc6287afabc2887366b0eb226c2
        Author: David Howells <dhowells@...hat.com>
        Date:   Thu Jan 8 12:04:47 2009 +0000

[2] List of all files there kdebug was defined:
* arch/mn10300/kernel/mn10300-serial.c
* arch/mn10300/mm/misalignment.c
* fs/cachefiles/internal.h
* fs/afs/internal.h
* fs/fscache/internal.h
* fs/binfmt_elf_fdpic.c
* kernel/cred.c
* mm/nommu.c
* net/rxrpc/ar-internal.h
* security/keys/internal.h

Thank you.

-- 
Leon Romanovsky | Independent Linux Consultant
        www.leon.nu | leon@...n.nu
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