Re: NL80211_CMD_GET_WIPHY reply doesn't fit into nl message buffer

[Jiri Slaby <jirislaby@gmail.com>]

On 09/29/2008 01:55 PM, Johannes Berg wrote:
> On Mon, 2008-09-29 at 13:52 +0200, Jiri Slaby wrote:
> 
>> --- a/net/wireless/nl80211.c
>> +++ b/net/wireless/nl80211.c
>> @@ -246,16 +246,26 @@ static int nl80211_get_wiphy(struct sk_buff *skb, struct
>> genl_info *info)
>>  {
>>         struct sk_buff *msg;
>>         struct cfg80211_registered_device *dev;
>> +       size_t bufsize = NLMSG_GOODSIZE;
>> +       unsigned int tries = 0;
>> +       int ret;
>>
>>         dev = cfg80211_get_dev_from_info(info);
>>         if (IS_ERR(dev))
>>                 return PTR_ERR(dev);
>>
>> -       msg = nlmsg_new(NLMSG_GOODSIZE, GFP_KERNEL);
>> +retry:
>> +       msg = nlmsg_new(bufsize, GFP_KERNEL);
>>         if (!msg)
>>                 goto out_err;
>>
>> -       if (nl80211_send_wiphy(msg, info->snd_pid, info->snd_seq, 0, dev) < 0)
>> +       ret = nl80211_send_wiphy(msg, info->snd_pid, info->snd_seq, 0, dev);
>> +       if (ret == -EMSGSIZE && ++tries < 2) {
>> +               bufsize *= 2;
>> +               nlmsg_free(msg);
>> +               goto retry;
>> +       }
>> +       if (ret < 0)
>>                 goto out_free;
>>
>>         cfg80211_put_dev(dev);
>>
> 
> Works for me. Not the greatest way to do this I guess, but hey, it
> works.

Anyway it is wrong. NLMSG_GOODSIZE * x for x > 1 doesn't give skb aligned to a
page boundary. bufsize should start with PAGE_SIZE or 8192 and be multiplied
then and the parameter used for nlmsg_new SKB_WITH_OVERHEAD(bufsize).

But it's ugly as hell, I agree -- and quite a temporary solution until somebody
decides to add channels, another channel info or whatever.