Subject: Re: [PATCH v1] net: Add distinct sk_psock field

From: Jakub Kicinski <[email-masked]>
Date: Wed, 13 Jul 2022 18:51:36 -0700

On Wed, 13 Jul 2022 10:26:21 -0400 Chuck Lever wrote:
> The sk_psock facility populates the sk_user_data field with the
> address of an extra bit of metadata. User space sockets never
> populate the sk_user_data field, so this has worked out fine.
> 
> However, kernel socket consumers such as the RPC client and server
> do populate the sk_user_data field. The sk_psock() function cannot
> tell that the content of sk_user_data does not point to psock
> metadata, so it will happily return a pointer to something else,
> cast to a struct sk_psock.
> 
> Thus kernel socket consumers and psock currently cannot co-exist.
> 
> We could educate sk_psock() to return NULL if sk_user_data does
> not point to a struct sk_psock. However, a more general solution
> that enables full co-existence psock and other uses of sk_user_data
> might be more interesting.
> 
> Move the struct sk_psock address to its own pointer field so that
> the contents of the sk_user_data field is preserved.
> 
> Reviewed-by: Hannes Reinecke <[email-masked]>
> Signed-off-by: Chuck Lever <[email-masked]>

Thanks for posting separately. We already have the (somewhat
nondescript) SK_USER_DATA_BPF, can we use another bit for psock?
Or add a u8 user_data type and have TCP ULP reject if the type is
anything but psock. I'm not sure why psock is special to deserve 
its own pointer.