linux-kernel - Re: [PATCH 2/6] statfs: use << to align with fs header

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Date:   Fri, 13 Apr 2018 11:35:11 -0600
From:   Andreas Dilger <adilger@...ger.ca>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        linux-kernel@...r.kernel.org, serge@...lyn.com
Subject: Re: [PATCH 2/6] statfs: use << to align with fs header

On Apr 13, 2018, at 10:11 AM, Christian Brauner <christian.brauner@...ntu.com> wrote:
> 
> Consistenly use << to define ST_* constants. This also aligns them with
> their MS_* counterparts in fs.h

IMHO, using (1 << 10) makes the code harder to debug.  If you see a field
in a structure like 0x8354, it is non-trivial to map this to the ST_*
flags if they are declared in the form (1 << 10) or BIT(10).  If they are
declared in the form 0x100 (as they are now) then it is trivial that the
ST_APPEND flag is set in 0x8354, and easy to understand the other flags.

So, my preference would be to NOT land this or the previous patch.

Cheers, Andreas

> Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
> ---
> include/linux/statfs.h | 26 +++++++++++++-------------
> 1 file changed, 13 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/statfs.h b/include/linux/statfs.h
> index 3142e98546ac..b336c04e793c 100644
> --- a/include/linux/statfs.h
> +++ b/include/linux/statfs.h
> @@ -27,18 +27,18 @@ struct kstatfs {
>  * ABI.  The exception is ST_VALID which has the same value as MS_REMOUNT
>  * which doesn't make any sense for statfs.
>  */
> -#define ST_RDONLY	0x0001	/* mount read-only */
> -#define ST_NOSUID	0x0002	/* ignore suid and sgid bits */
> -#define ST_NODEV	0x0004	/* disallow access to device special files */
> -#define ST_NOEXEC	0x0008	/* disallow program execution */
> -#define ST_SYNCHRONOUS	0x0010	/* writes are synced at once */
> -#define ST_VALID	0x0020	/* f_flags support is implemented */
> -#define ST_MANDLOCK	0x0040	/* allow mandatory locks on an FS */
> -/* 0x0080 used for ST_WRITE in glibc */
> -/* 0x0100 used for ST_APPEND in glibc */
> -/* 0x0200 used for ST_IMMUTABLE in glibc */
> -#define ST_NOATIME	0x0400	/* do not update access times */
> -#define ST_NODIRATIME	0x0800	/* do not update directory access times */
> -#define ST_RELATIME	0x1000	/* update atime relative to mtime/ctime */
> +#define ST_RDONLY	(1<<0) /* mount read-only */
> +#define ST_NOSUID	(1<<1) /* ignore suid and sgid bits */
> +#define ST_NODEV	(1<<2) /* disallow access to device special files */
> +#define ST_NOEXEC	(1<<3) /* disallow program execution */
> +#define ST_SYNCHRONOUS	(1<<4) /* writes are synced at once */
> +#define ST_VALID	(1<<5) /* f_flags support is implemented */
> +#define ST_MANDLOCK	(1<<6) /* allow mandatory locks on an FS */
> +/* (1<<7) used for ST_WRITE in glibc */
> +/* (1<<8) used for ST_APPEND in glibc */
> +/* (1<<9) used for ST_IMMUTABLE in glibc */
> +#define ST_NOATIME	(1<<10) /* do not update access times */
> +#define ST_NODIRATIME	(1<<11) /* do not update directory access times */
> +#define ST_RELATIME	(1<<12) /* update atime relative to mtime/ctime */
> 
> #endif
> --
> 2.17.0
> 


Cheers, Andreas






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