linux-kernel - Re: [PATCH v2 10/24] ioctl_ns.2: Cast to 'unsigned long' rather than 'long' when printing with "%lx"

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Date:   Fri, 11 Sep 2020 11:18:21 +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 v2 10/24] ioctl_ns.2: Cast to 'unsigned long' rather than
 'long' when printing with "%lx"

On 9/11/20 11:13 AM, Alejandro Colomar wrote:
> Hi Michael,
> 
> On 2020-09-11 09:24, Michael Kerrisk (man-pages) wrote:
>> 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')
> 
> Fine, then here is the patch with the casts to 'unsigned long'.

Thanks. Patch applied.

Cheers,

Michael

> -------------------------------------------------------------
>  From c5f644e798ffc5dec0c73f324a26059568865c68 Mon Sep 17 00:00:00 2001
> From: Alejandro Colomar <colomar.6.4.3@...il.com>
> Date: Fri, 11 Sep 2020 10:51:26 +0200
> Subject: [PATCH v2 10/24] ioctl_ns.2: Cast to 'unsigned long' rather 
> than 'long'
>   when printing with "%lx"
> 
>  From the email conversation:
> 
> On 2020-09-11 09:24, Michael Kerrisk (man-pages) wrote:
>  > 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 | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/man2/ioctl_ns.2 b/man2/ioctl_ns.2
> index 818dde32c..8b8789d1f 100644
> --- a/man2/ioctl_ns.2
> +++ b/man2/ioctl_ns.2
> @@ -317,7 +317,8 @@ main(int argc, char *argv[])
>           }
>           printf("Device/Inode of owning user namespace is: "
>                   "[%lx,%lx] / %ld\en",
> -                (long) major(sb.st_dev), (long) minor(sb.st_dev),
> +                (unsigned long) major(sb.st_dev),
> +                (unsigned long) minor(sb.st_dev),
>                   (long) sb.st_ino);
> 
>           close(userns_fd);
> @@ -346,7 +347,8 @@ main(int argc, char *argv[])
>               exit(EXIT_FAILURE);
>           }
>           printf("Device/Inode of parent namespace is: [%lx,%lx] / %ld\en",
> -                (long) major(sb.st_dev), (long) minor(sb.st_dev),
> +                (unsigned long) major(sb.st_dev),
> +                (unsigned long) 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/