netdev - Re: [PATCH v4] net: fully namespace net.core.{r,w}mem

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Message-ID: <CAFnufp14ap0UfJcn2uwU4-3cstr313J86HvRCcKULZLRU=nZ6Q@mail.gmail.com>
Date: Fri, 18 Apr 2025 12:10:23 +0200
From: Matteo Croce <technoboy85@...il.com>
To: Danny Lin <danny@...stack.dev>, netdev@...r.kernel.org
Cc: Matteo Croce <teknoraver@...a.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Simon Horman <horms@...nel.org>, David Ahern <dsahern@...nel.org>, linux-kernel@...r.kernel.org, 
	Shakeel Butt <shakeel.butt@...ux.dev>
Subject: Re: [PATCH v4] net: fully namespace net.core.{r,w}mem_{default,max} sysctls

Il giorno ven 18 apr 2025 alle ore 12:06 Danny Lin
<danny@...stack.dev> ha scritto:
>
> This builds on commit 19249c0724f2 ("net: make net.core.{r,w}mem_{default,max} namespaced")
> by adding support for writing the sysctls from within net namespaces,
> rather than only reading the values that were set in init_net. These are
> relatively commonly-used sysctls, so programs may try to set them without
> knowing that they're in a container. It can be surprising for such attempts
> to fail with EACCES.
>
> Unlike other net sysctls that were converted to namespaced ones, many
> systems have a sysctl.conf (or other configs) that globally write to
> net.core.rmem_default on boot and expect the value to propagate to
> containers, and programs running in containers may depend on the increased
> buffer sizes in order to work properly. This means that namespacing the
> sysctls and using the kernel default values in each new netns would break
> existing workloads.
>
> As a compromise, inherit the initial net.core.*mem_* values from the
> current process' netns when creating a new netns. This is not standard
> behavior for most netns sysctls, but it avoids breaking existing workloads.
>
> Signed-off-by: Danny Lin <danny@...stack.dev>

Hi,

does this allow to set, in a namespace, a larger buffer than the one
in the init namespace?

Regards,
-- 
Matteo Croce

perl -e 'for($t=0;;$t++){print chr($t*($t>>8|$t>>13)&255)}' |aplay