Re: [PATCH] man/man3/errno.3: clarify ENOTSUP and EOPNOTSUPP

Alejandro Colomar <[email protected]> Thu, 28 May 2026 00:59:44 +0200

Newsgroups	org.kernel.vger.linux-man,org.kernel.vger.linux-fsdevel,org.kernel.vger.linux-kernel
Message-ID	<ahd3SmZZqnzP0-O2@devuan>

Hi Askar,

On 2026-05-27T18:15:48+0000, Askar Safin wrote:
> As revealed by Christian Brauner recently
> ( https://lore.kernel.org/all/20260527-fotowettbewerb-abwinken-einfach-83db3411945b@brauner/ ),
> EOPNOTSUPP is widely used on Linux to mean "Operation not supported",
> as opposed to "Operation not supported on socket".
> 
> Also, as seen in POSIX issue 8:
> https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/errno.h.html
> POSIX doesn't require ENOTSUP and EOPNOTSUPP to be distinct, so
> let's update that, too.
> 
> Signed-off-by: Askar Safin <[email protected]>

I've applied the patch; thanks!


Have a lovely night!
Alex

> ---
>  man/man3/errno.3 | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/man/man3/errno.3 b/man/man3/errno.3
> index a070dab..fdd2710 100644
> --- a/man/man3/errno.3
> +++ b/man/man3/errno.3
> @@ -477,13 +477,14 @@ Name not unique on network.
>  No such device or address (POSIX.1-2001).
>  .TP
>  .B EOPNOTSUPP
> -Operation not supported on socket (POSIX.1-2001).
> +Operation not supported (POSIX.1-2001).
> +According to POSIX.1 this is "Operation not supported on socket",
> +but on Linux it effectively means just "Operation not supported".
>  .IP
>  .RB ( ENOTSUP
>  and
>  .B EOPNOTSUPP
> -have the same value on Linux, but
> -according to POSIX.1 these error values should be distinct.)
> +have the same value on Linux.)
>  .TP
>  .B EOVERFLOW
>  Value too large to be stored in data type (POSIX.1-2001).
> 
> base-commit: 9a4bfd0e50745c2649b6291db40b58e37c9c1c6b
> -- 
> 2.47.3
> 

-- 
<https://www.alejandro-colomar.es>

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