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From: Michael Ellerman <mpe@ellerman.id.au>
To: Ingo Molnar <mingo@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
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        linux-mm <linux-mm@kvack.org>, michael.schwarz@iaik.tugraz.at,
        moritz.lipp@iaik.tugraz.at, richard.fellner@student.tugraz.at
Subject: Re: [PATCH] vfs: Add PERM_* symbolic helpers for common file mode/permissions
In-Reply-To: <20171128111214.42esi4igzgnldsx5@gmail.com>
References: <20171126231403.657575796@linutronix.de> <20171126232414.563046145@linutronix.de> <20171127094156.rbq7i7it7ojsblfj@hirez.programming.kicks-ass.net> <20171127100635.kfw2nspspqbrf2qm@gmail.com> <CA+55aFyLC9+S=MZueRXMmwwnx47bhovXr1YhRg+FAPFfQZXoYA@mail.gmail.com> <20171128111214.42esi4igzgnldsx5@gmail.com>
Date: Wed, 29 Nov 2017 19:52:56 +1100
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Ingo Molnar <mingo@kernel.org> writes:
...
> Index: tip/include/linux/stat.h
> ===================================================================
> --- tip.orig/include/linux/stat.h
> +++ tip/include/linux/stat.h
> @@ -6,6 +6,34 @@
>  #include <asm/stat.h>
>  #include <uapi/linux/stat.h>
>  
> +/*
> + * Human readable symbolic definitions for common
> + * file permissions:
> + */
> +#define PERM_r________	0400
> +#define PERM_r__r_____	0440
> +#define PERM_r__r__r__	0444
> +
> +#define PERM_rw_______	0600
> +#define PERM_rw_r_____	0640
> +#define PERM_rw_r__r__	0644
> +#define PERM_rw_rw_r__	0664
> +#define PERM_rw_rw_rw_	0666
> +
> +#define PERM__w_______	0200
> +#define PERM__w__w____	0220
> +#define PERM__w__w__w_	0222
> +
> +#define PERM_r_x______	0500
> +#define PERM_r_xr_x___	0550
> +#define PERM_r_xr_xr_x	0555
> +
> +#define PERM_rwx______	0700
> +#define PERM_rwxr_x___	0750
> +#define PERM_rwxr_xr_x	0755
> +#define PERM_rwxrwxr_x	0775
> +#define PERM_rwxrwxrwx	0777

I see what you're trying to do with all the explicit underscores, but it
does make them look kinda ugly.

What if you just used underscores to separate the user/group/other, and
the unset permission bits are just omitted.

Then the two most common cases would be:

  PERM_rw_r_r
  PERM_r_r_r

Both of those read nicely I think. ie. the first is "perm read write,
read, read".

Full set would be:

#define PERM_r			0400
#define PERM_r_r		0440
#define PERM_r_r_r		0444

#define PERM_rw			0600
#define PERM_rw_r		0640
#define PERM_rw_r_r		0644
#define PERM_rw_rw_r		0664
#define PERM_rw_rw_rw		0666

#define PERM_w			0200
#define PERM_w_w		0220
#define PERM_w_w_w		0222

#define PERM_rx			0500
#define PERM_rx_rx		0550
#define PERM_rx_rx_rx		0555

#define PERM_rwx		0700
#define PERM_rwx_rx		0750
#define PERM_rwx_rx_rx		0755
#define PERM_rwx_rwx_rx		0775
#define PERM_rwx_rwx_rwx	0777


cheers