netdev - Re: [PATCH 4/6] net: add NL802154 interface for configuration of 802.15.4 devices

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Date:	Thu, 4 Jun 2009 19:14:28 +0400
From:	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	Johannes Berg <johannes@...solutions.net>,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	linux-wireless@...r.kernel.org, sfr@...b.auug.org.au,
	slapin@...fans.org
Subject: Re: [PATCH 4/6] net: add NL802154 interface for configuration of 
	802.15.4 devices

2009/6/4 Patrick McHardy <kaber@...sh.net>:
> Dmitry Eremin-Solenikov wrote:
>>
>> 2009/6/4 Johannes Berg <johannes@...solutions.net>:
>>>
>>> On Wed, 2009-06-03 at 16:27 +0400, Dmitry Eremin-Solenikov wrote:
>>>
>>>>>> +static int ieee802154_nl_put_failure(struct sk_buff *msg)
>>>>>> +{
>>>>>> + void *hdr = genlmsg_data(NLMSG_DATA(msg->data)); /* XXX: nlh is
>>>>>> right at the start of msg */
>>>>>> + genlmsg_cancel(msg, hdr);
>>>>>> + nlmsg_free(msg);
>>>>>> + return -ENOBUFS;
>>>>>> +}
>>>>>
>>>>> This seems weird.
>>>>
>>>> Why?
>>>
>>> Because it's strange to cancel then free?
>>
>>> From looking at the other code, the usual pattern for netlink is
>>
>> (please, correct me if I'm wrong):
>>
>> int fill (....)
>> {
>>   genlmsg_put();
>>   NLA_PUT(...)
>>   NLA_PUT(...)
>>   return genlmsg_end();
>>
>> nla_put_failure:
>>   genlmsg_cancel();
>>   return -EMSGSIZE;
>> }
>>
>> int cmd(...)
>> {
>>    int rc;
>>    nlmsg_new();
>>
>>    rc = fill();
>>    if (rc < 0)
>>        goto out;
>>
>>    genlmsg_unicast();
>>
>> out:
>>    nlmsg_free();
>>    return -ENOBUFS;
>> }
>>
>> This is equivalent to our code:
>>
>> sk_buff *new()
>> {
>>   msg = nlmsg_new();
>>   genlmsg_put();
>>   return msg;
>> }
>
> canceling messages is only necessary in fill functions that are
> also used for dumps, where as many elements are stuffed in the
> skb as possible. When the last element doesn't completely fit,
> its removed again (canceled) and put into the next skb.

Understood. So you'd suggest just to drop the genlmsg_cancel()
from the failure call chain?


-- 
With best wishes
Dmitry
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