netdev - Re: [PATCH 0/5] Rust abstractions for network device drivers

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Date: Fri, 16 Jun 2023 11:40:06 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: FUJITA Tomonori <fujita.tomonori@...il.com>
Cc: andrew@...n.ch, netdev@...r.kernel.org, rust-for-linux@...r.kernel.org,
 aliceryhl@...gle.com, miguel.ojeda.sandonis@...il.com
Subject: Re: [PATCH 0/5] Rust abstractions for network device drivers

On Fri, 16 Jun 2023 22:02:20 +0900 (JST) FUJITA Tomonori wrote:
> > The skb freeing looks shady from functional perspective.
> > I'm guessing some form of destructor frees the skb automatically
> > in xmit handler(?), but (a) no reason support, (b) kfree_skb_reason()
> > is most certainly not safe to call on all xmit paths...  
> 
> Yeah, I assume that a driver keeps a skb in private data structure
> (such as tx ring) then removes the skb from it after the completion of
> tx; automatically the drop() method runs (where we need to free the
> skb).
> 
> I thought that calling dev_kfree_skb() is fine but no? We also need
> something different for drivers that use other ways to free the skb
> though.
> 
> I use kfree_skb_reason() because dev_kfree_skb() is a macro so it
> can't be called directly from Rust. But I should have used
> dev_kfree_skb() with a helper function.

skbs (generally) can't be freed in an interrupt context.
dev_kfree_skb_any_reason() is probably the most general implementation.
But then we also have a set of functions used in known contexts for fast
object recycling like napi_consume_skb().
How would complex object destruction rules fit in in the Rust world?