linux-kernel - Re: [PATCH] proc: Convert S_<FOO> permission uses to octal

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Message-ID: <20210212221918.GA2858050@casper.infradead.org>
Date:   Fri, 12 Feb 2021 22:19:18 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Joe Perches <joe@...ches.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] proc: Convert S_<FOO> permission uses to octal

On Fri, Feb 12, 2021 at 04:01:48PM -0600, Eric W. Biederman wrote:
> Joe Perches <joe@...ches.com> writes:
> 
> > Convert S_<FOO> permissions to the more readable octal.
> >
> > Done using:
> > $ ./scripts/checkpatch.pl -f --fix-inplace --types=SYMBOLIC_PERMS fs/proc/*.[ch]
> >
> > No difference in generated .o files allyesconfig x86-64
> >
> > Link:
> > https://lore.kernel.org/lkml/CA+55aFw5v23T-zvDZp-MmD_EYxF8WbafwwB59934FV7g21uMGQ@mail.gmail.com/
> 
> 
> I will be frank.  I don't know what 0644 means.  I can never remember
> which bit is read, write or execute.  So I like symbolic constants.

Heh, I'm the other way, I can't remember what S_IRUGO means.

but I think there's another way which improves the information
density:

#define DIR_RO_ALL(NAME, iops, fops)	DIR(NAME, 0555, iops, fops)
...
(or S_IRUGO or whatever expands to 0555)

There's really only a few combinations --
	root read-only,
	everybody read-only
	root-write, others-read
	everybody-write

and execute is only used by proc for directories, not files, so I think
there's only 8 combinations we'd need (and everybody-write is almost
unused ...)

> Perhaps we can do something like:
> 
> #define S_IRWX 7
> #define S_IRW_ 6
> #define S_IR_X 5
> #define S_IR__ 4
> #define S_I_WX 3
> #define S_I_W_ 2
> #define S_I__X 1
> #define S_I___ 0
> 
> #define MODE(TYPE, USER, GROUP, OTHER) \
> 	(((S_IF##TYPE) << 9) | \
>          ((S_I##USER)  << 6) | \
>          ((S_I##GROUP) << 3) | \
>          (S_I##OTHER))
> 
> Which would be used something like:
> MODE(DIR, RWX, R_X, R_X)
> MODE(REG, RWX, R__, R__)
> 
> Something like that should be able to address the readability while
> still using symbolic constants.

I think that's been proposed before.