linux-kernel - Re: [PATCH 10/24] ioctl_ns.2: Remove unneeded cast

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Date:   Fri, 11 Sep 2020 09:24:44 +0200
From:   "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:     Alejandro Colomar <colomar.6.4.3@...il.com>
Cc:     mtk.manpages@...il.com, linux-man@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/24] ioctl_ns.2: Remove unneeded cast

Hi Alex,

On 9/10/20 11:13 PM, Alejandro Colomar wrote:
> Both major(3) and minor(3) return an 'unsigned int',
> so there is no need to use a 'long' for printing.
> Moreover, it should have been 'unsigned long',
> as "%lx" expects an unsigned type.

This may be true on Linux, but is not true on other systems.
For example, on HP-UX, according to one header file I'm 
looking at, the return value is 'long'.

These kinds of casts are intended to improve code portability
across UNIX implementations, so I think they should stay
(although, I do wonder if they would be even better as casts 
to 'unsigned long')

Thanks,

Michael


> Signed-off-by: Alejandro Colomar <colomar.6.4.3@...il.com>
> ---
>  man2/ioctl_ns.2 | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/man2/ioctl_ns.2 b/man2/ioctl_ns.2
> index 818dde32c..bf832a2c7 100644
> --- a/man2/ioctl_ns.2
> +++ b/man2/ioctl_ns.2
> @@ -316,9 +316,8 @@ main(int argc, char *argv[])
>              exit(EXIT_FAILURE);
>          }
>          printf("Device/Inode of owning user namespace is: "
> -                "[%lx,%lx] / %ld\en",
> -                (long) major(sb.st_dev), (long) minor(sb.st_dev),
> -                (long) sb.st_ino);
> +                "[%x,%x] / %ld\en",
> +                major(sb.st_dev), minor(sb.st_dev), (long) sb.st_ino);
>  
>          close(userns_fd);
>      }
> @@ -345,9 +344,8 @@ main(int argc, char *argv[])
>              perror("fstat\-parentns");
>              exit(EXIT_FAILURE);
>          }
> -        printf("Device/Inode of parent namespace is: [%lx,%lx] / %ld\en",
> -                (long) major(sb.st_dev), (long) minor(sb.st_dev),
> -                (long) sb.st_ino);
> +        printf("Device/Inode of parent namespace is: [%x,%x] / %ld\en",
> +                major(sb.st_dev), minor(sb.st_dev), (long) sb.st_ino);
>  
>          close(parent_fd);
>      }
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/