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

From: Andreas Dilger
Date: Fri Apr 13 2018 - 13:35:41 EST


On Apr 13, 2018, at 10:11 AM, Christian Brauner <christian.brauner@xxxxxxxxxx> 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@xxxxxxxxxx>
> ---
> 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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