linux-kernel - Re: Please don't replace numeric parameter like 0444 with macro

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Date:	Wed, 3 Aug 2016 11:07:28 +0300
From:	Konstantin Khlebnikov <koct9i@...il.com>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Russell King - ARM Linux <linux@...linux.org.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Baole Ni <baolex.ni@...el.com>, Pavel Machek <pavel@....cz>,
	chuansheng.liu@...el.com,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: Please don't replace numeric parameter like 0444 with macro

On Wed, Aug 3, 2016 at 3:42 AM, Al Viro <viro@...iv.linux.org.uk> wrote:
> On Tue, Aug 02, 2016 at 04:58:29PM -0400, Linus Torvalds wrote:
>> [ So I answered similarly to another patch, but I'll just re-iterate
>> and change the subject line so that it stands out a bit from the
>> millions of actual patches ]
>>
>> On Tue, Aug 2, 2016 at 1:42 PM, Pavel Machek <pavel@....cz> wrote:
>> >
>> > Everyone knows what 0644 is, but noone can read S_IRUSR | S_IWUSR |
>> > S_IRCRP | S_IROTH (*). Please don't do this.
>>
>> Absolutely. It's *much* easier to parse and understand the octal
>> numbers, while the symbolic macro names are just random line noise and
>> hard as hell to understand. You really have to think about it.
>>
>> So we should rather go the other way: convert existing bad symbolic
>> permission bit macro use to just use the octal numbers.
>>
>> The symbolic names are good for the *other* bits (ie sticky bit, and
>> the inode mode _type_ numbers etc), but for the permission bits, the
>> symbolic names are just insane crap. Nobody sane should ever use them.
>> Not in the kernel, not in user space.
>
> Except that you are inviting the mixes like S_IFDIR | 17 /* oops, should've
> been 017, or do we spell it 0017? */ that way.  I certainly agree that this
> patch series had been a huge pile of manure, but "let's convert it in other
> direction" is inviting pretty much the same thing, with lovely potential for
> typos, etc.

We could add several macro with readable names for really used rwx
combinations, like:

#define KERN_SECRET_RO 0400
#define KERN_SECRET_RW 0600
#define KERN_SECRET_WO 0200
#define KERN_SECRET_DIR 0500

#define KERN_PUBLIC_RO 0444
#define KERN_PUBLIC_RW 0644
#define KERN_PUBLIC_DIR 0555

#define KERN_UNSAFE_RW 0666
#define KERN_UNSAFE_WO 0222
#define KERN_UNSAFE_DIR 0777

>
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