# Re: \[PATCH\] include/net/genetlink.h: Allow genlmsg\_cancel to accept a NULL argument

- From: David Miller \<davem@davemloft.net\>
- Date: 2011-02-01 22:53:36 
- List: netdev
- Page: https://ratatoskr.run/netdev/2011/02/3672461
- Thread: https://ratatoskr.run/netdev/2011/01/3671082/t.md

```text
From: Julia Lawall <redacted>
Date: Fri, 28 Jan 2011 16:43:40 +0100 (CET)

> nlmsg_cancel can accept NULL as its second argument, so for similarity,
> this patch extends genlmsg_cancel to be able to accept a NULL second
> argument as well.
> 
> Signed-off-by: Julia Lawall <redacted>

I did a scan of all of the cases where this interface is used, and
I cannot find a situation where this capability would even be useful.

The use pattern is always:

	hdr = genlmsg_put(skb, ...);
	if (!hdr)
		goto out;

	NLA_PUT_*();
	NLA_PUT_*();
	....

	return genlmsg_end(skb, hdr);

nla_put_failure:
	genlmsg_cancel(skb, hdr);
out:
	return -EWHATEVER;

Always, hdr will be non-NULL.

We have to allocate the header first, then put the netlink
attributes.

Looking over users of nlmsg_cancel(), the situation seems to
match identically.

Therefore, it seems to me that it makes more sense to remove
the NULL check from nlmsg_cancel() than to add the NULL check
to genlmsg_cancel().

Thanks.
```