man/man3/errno.3: clarify ENOTSUP and EOPNOTSUPP

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

Posted by Askar Safin 1 week, 4 days ago

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 <safinaskar@gmail.com>
---
 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

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

Posted by Alejandro Colomar 1 week, 4 days ago

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 <safinaskar@gmail.com>

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>