From: Bobby Eshleman <bobbyeshleman@meta.com>

Update the vsock child_ns_mode documentation to include the new the
write-once semantics of setting child_ns_mode. The semantics are
implemented in a different patch in this series.

Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
---
 Documentation/admin-guide/sysctl/net.rst | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst
index c10530624f1e..976a176fb451 100644
--- a/Documentation/admin-guide/sysctl/net.rst
+++ b/Documentation/admin-guide/sysctl/net.rst
@@ -581,9 +581,9 @@ The init_net mode is always ``global``.
 child_ns_mode
 -------------
 
-Controls what mode newly created child namespaces will inherit. At namespace
-creation, ``ns_mode`` is inherited from the parent's ``child_ns_mode``. The
-initial value matches the namespace's own ``ns_mode``.
+Write-once. Controls what mode newly created child namespaces will inherit. At
+namespace creation, ``ns_mode`` is inherited from the parent's
+``child_ns_mode``. The initial value matches the namespace's own ``ns_mode``.
 
 Values:
 
@@ -594,6 +594,10 @@ Values:
 	  their sockets will only be able to connect within their own
 	  namespace.
 
+``child_ns_mode`` can only be written once per namespace. Writing the same
+value that is already set succeeds. Writing a different value after the first
+write returns ``-EBUSY``.
+
 Changing ``child_ns_mode`` only affects namespaces created after the change;
 it does not modify the current namespace or any existing children.
 

-- 
2.47.3

On Wed, Feb 18, 2026 at 10:10:38AM -0800, Bobby Eshleman wrote:
>From: Bobby Eshleman <bobbyeshleman@meta.com>
>
>Update the vsock child_ns_mode documentation to include the new the

nit: s/the new the/the new

>write-once semantics of setting child_ns_mode. The semantics are
>implemented in a different patch in this series.

s/different/preceding ?

IMO this can be squashed with the previous patch, but not sure netdev 
policy about that. Not a strong opinion, it's fine also in this way.

>
>Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
>---
> Documentation/admin-guide/sysctl/net.rst | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
>diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst
>index c10530624f1e..976a176fb451 100644
>--- a/Documentation/admin-guide/sysctl/net.rst
>+++ b/Documentation/admin-guide/sysctl/net.rst
>@@ -581,9 +581,9 @@ The init_net mode is always ``global``.
> child_ns_mode
> -------------
>
>-Controls what mode newly created child namespaces will inherit. At namespace
>-creation, ``ns_mode`` is inherited from the parent's ``child_ns_mode``. The
>-initial value matches the namespace's own ``ns_mode``.
>+Write-once. Controls what mode newly created child namespaces will inherit. At
>+namespace creation, ``ns_mode`` is inherited from the parent's
>+``child_ns_mode``. The initial value matches the namespace's own ``ns_mode``.
>
> Values:
>
>@@ -594,6 +594,10 @@ Values:
> 	  their sockets will only be able to connect within their own
> 	  namespace.
>
>+``child_ns_mode`` can only be written once per namespace. Writing the same
>+value that is already set succeeds. Writing a different value after the first
>+write returns ``-EBUSY``.

nit: instead of saying that it can only be written once, we could say 
that the first write locks the value, to be closer to the actual 
behavior, something like this: 

   The first write to ``child_ns_mode`` locks its value. Subsequent
   writes of the same value succeed, but writing a different value
   returns ``-EBUSY``.


Thanks,
Stefano

>+
> Changing ``child_ns_mode`` only affects namespaces created after the change;
> it does not modify the current namespace or any existing children.
>
>
>-- 
>2.47.3
>

On Thu, Feb 19, 2026 at 11:36:40AM +0100, Stefano Garzarella wrote:
> On Wed, Feb 18, 2026 at 10:10:38AM -0800, Bobby Eshleman wrote:
> > From: Bobby Eshleman <bobbyeshleman@meta.com>
> > 
> > Update the vsock child_ns_mode documentation to include the new the
> 
> nit: s/the new the/the new
> 
> > write-once semantics of setting child_ns_mode. The semantics are
> > implemented in a different patch in this series.
> 
> s/different/preceding ?
> 
> IMO this can be squashed with the previous patch, but not sure netdev policy
> about that. Not a strong opinion, it's fine also in this way.
> 
> > 
> > Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
> > ---
> > Documentation/admin-guide/sysctl/net.rst | 10 +++++++---
> > 1 file changed, 7 insertions(+), 3 deletions(-)
> > 
> > diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst
> > index c10530624f1e..976a176fb451 100644
> > --- a/Documentation/admin-guide/sysctl/net.rst
> > +++ b/Documentation/admin-guide/sysctl/net.rst
> > @@ -581,9 +581,9 @@ The init_net mode is always ``global``.
> > child_ns_mode
> > -------------
> > 
> > -Controls what mode newly created child namespaces will inherit. At namespace
> > -creation, ``ns_mode`` is inherited from the parent's ``child_ns_mode``. The
> > -initial value matches the namespace's own ``ns_mode``.
> > +Write-once. Controls what mode newly created child namespaces will inherit. At
> > +namespace creation, ``ns_mode`` is inherited from the parent's
> > +``child_ns_mode``. The initial value matches the namespace's own ``ns_mode``.
> > 
> > Values:
> > 
> > @@ -594,6 +594,10 @@ Values:
> > 	  their sockets will only be able to connect within their own
> > 	  namespace.
> > 
> > +``child_ns_mode`` can only be written once per namespace. Writing the same
> > +value that is already set succeeds. Writing a different value after the first
> > +write returns ``-EBUSY``.
> 
> nit: instead of saying that it can only be written once, we could say that
> the first write locks the value, to be closer to the actual behavior,
> something like this:
> 
>   The first write to ``child_ns_mode`` locks its value. Subsequent
>   writes of the same value succeed, but writing a different value
>   returns ``-EBUSY``.
> 
> 
> Thanks,
> Stefano

Sounds good! I agree that is more clear. I'll also remove the change
above that adds "Write-once" at the beginning of the paragraph, since
this clause does a better job explaining how it actually works.

> 
> > +
> > Changing ``child_ns_mode`` only affects namespaces created after the change;
> > it does not modify the current namespace or any existing children.
> > 
> > 
> > -- 
> > 2.47.3
> > 
>