linux-kernel - Re: [PATCH 1/6] fs: use << for MS

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Date:   Fri, 13 Apr 2018 09:45:01 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Christian Brauner <christian.brauner@...ntu.com>,
        viro@...iv.linux.org.uk, tglx@...utronix.de,
        kstewart@...uxfoundation.org, gregkh@...uxfoundation.org,
        pombredanne@...b.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, serge@...lyn.com
Subject: Re: [PATCH 1/6] fs: use << for MS_* flags

On 04/13/2018 09:11 AM, Christian Brauner wrote:
> Consistenly use << to define MS_* constants.
> 
> Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
> ---
>  include/uapi/linux/fs.h | 33 +++++++++++++++++----------------
>  1 file changed, 17 insertions(+), 16 deletions(-)
> 
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index d2a8313fabd7..9662790a657c 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -105,22 +105,23 @@ struct inodes_stat_t {
>  /*
>   * These are the fs-independent mount-flags: up to 32 flags are supported
>   */
> -#define MS_RDONLY	 1	/* Mount read-only */
> -#define MS_NOSUID	 2	/* Ignore suid and sgid bits */
> -#define MS_NODEV	 4	/* Disallow access to device special files */
> -#define MS_NOEXEC	 8	/* Disallow program execution */
> -#define MS_SYNCHRONOUS	16	/* Writes are synced at once */
> -#define MS_REMOUNT	32	/* Alter flags of a mounted FS */
> -#define MS_MANDLOCK	64	/* Allow mandatory locks on an FS */
> -#define MS_DIRSYNC	128	/* Directory modifications are synchronous */
> -#define MS_NOATIME	1024	/* Do not update access times. */
> -#define MS_NODIRATIME	2048	/* Do not update directory access times */
> -#define MS_BIND		4096
> -#define MS_MOVE		8192
> -#define MS_REC		16384
> -#define MS_VERBOSE	32768	/* War is peace. Verbosity is silence.
> -				   MS_VERBOSE is deprecated. */
> -#define MS_SILENT	32768
> +#define MS_RDONLY	(1<<0)	/* Mount read-only */

Why not just use BIT(n) instead?

#include <linux/bitops.h>

#define MS_RDONLY	BIT(0)	/* Mount read-only */

etc.

> +#define MS_NOSUID	(1<<1)	/* Ignore suid and sgid bits */
> +#define MS_NODEV	(1<<2)	/* Disallow access to device special files */
> +#define MS_NOEXEC	(1<<3)	/* Disallow program execution */
> +#define MS_SYNCHRONOUS	(1<<4)	/* Writes are synced at once */
> +#define MS_REMOUNT	(1<<5)	/* Alter flags of a mounted FS */
> +#define MS_MANDLOCK	(1<<6)	/* Allow mandatory locks on an FS */
> +#define MS_DIRSYNC	(1<<7)	/* Directory modifications are synchronous */
> +#define MS_NOATIME	(1<<10)	/* Do not update access times. */
> +#define MS_NODIRATIME	(1<<11)	/* Do not update directory access times */
> +#define MS_BIND		(1<<12)
> +#define MS_MOVE		(1<<13)
> +#define MS_REC		(1<<14)
> +#define MS_VERBOSE	(1<<15)	/* War is peace. Verbosity is silence.
> +				 * MS_VERBOSE is deprecated.
> +				 */
> +#define MS_SILENT	(1<<15)
>  #define MS_POSIXACL	(1<<16)	/* VFS does not apply the umask */
>  #define MS_UNBINDABLE	(1<<17)	/* change to unbindable */
>  #define MS_PRIVATE	(1<<18)	/* change to private */
> 


-- 
~Randy