linux-kernel - Re: [PATCH v1] net: Add distinct sk

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Date:   Wed, 13 Jul 2022 18:51:36 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Chuck Lever <chuck.lever@...cle.com>
Cc:     john.fastabend@...il.com, daniel@...earbox.net,
        jakub@...udflare.com, davem@...emloft.net, edumazet@...gle.com,
        pabeni@...hat.com, ast@...nel.org, andrii@...nel.org, kafai@...com,
        songliubraving@...com, yhs@...com, kpsingh@...nel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] net: Add distinct sk_psock field

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 <hare@...e.de>
> Signed-off-by: Chuck Lever <chuck.lever@...cle.com>

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.