Re: [patch net-next v3 5/9] genetlink: implement release callback and free sk_user_data there

[Jiri Pirko <jiri@resnulli.us>]

Thu, Nov 23, 2023 at 05:24:08PM CET, kuba@kernel.org wrote:
>On Thu, 23 Nov 2023 11:32:07 +0100 Jiri Pirko wrote:
>> In this case, the socket is not opened by kernel, but it is opened by
>> the userspace app.
>> 
>> I basically need to have per-user-sk pointer somewhere I'm not clear why
>> to put it in struct netlink_sock when I can use sk_user_data which is
>> already there. From the usage of this pointer in kernel, I understand
>> this is exactly the reason to have it.
>
>Various people stuck various things in that pointer just because,
>it's a mess. IIUC the initial motivation for it is that someone
>like NFS opens a kernel socket and needs to put private data
>somewhere. A kernel user gets a callback for a socket, like data
>ready, and needs to find their private state.
>
>> Are you afraid of a collision of sk_user_data use with somebody else
>> here? I don't see how that could happen for netlink socket.
>
>Normally upper layer wraps the socket struct in its own struct. 
>Look at the struct nesting for TCP or any other bona fide protocol. 
>genetlink will benefit from having socket state, I bet it wasn't done
>that way from the start because Jamal/Thomas were told to start small.
>
>Please add a properly typed field to the netlink struct, unless you
>have technical reasons not to.

Okay.