Re: [PATCH v3] d80211: Add software sequence support

[Michael Buesch <mb@bu3sch.de>]

On Saturday 10 March 2007 20:21, Ivo van Doorn wrote:
> Most hardware can keep track of sequence numbers themselves,
> unfortunately *most* doesn't cover all devices. ;)
> This patch will keep track of the (per-bss) sequence number
> if the flag IEEE80211_HW_SOFTWARE_SEQUENCE has been set.

The question has been asked (by Jouni), but I didn't see
a good answer (maybe I missed it).
Why is this a flag at all? The sequence counter is such a
trivial thing that having an extra conditional is just _more_
overhead. Why not simply calculate the seq all the time and
let hardware override it, if it has the capability to do so?
Calculation of the seq is cheap. No need to bloat code.

> This 3rd version of the patch has the sequence number stored
> in the ieee80211_sub_if_data structure.
> 
> Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
> 
> ---
> 
> diff --git a/include/net/mac80211.h b/include/net/mac80211.h
> index 82ea43f..e32e28a 100644
> --- a/include/net/mac80211.h
> +++ b/include/net/mac80211.h
> @@ -515,6 +515,9 @@ struct ieee80211_hw {
>  	 * normal operation. */
>  #define IEEE80211_HW_MONITOR_DURING_OPER (1<<9)
>  
> +	/* Does the HOST need to insert the frame sequence counter */
> +#define IEEE80211_HW_SOFTWARE_SEQUENCE (1<<10)
> +
>  	/* please fill this gap when adding new flags */
>  
>  	/* calculate Michael MIC for an MSDU when doing hwcrypto */
> diff --git a/net/mac80211/ieee80211.c b/net/mac80211/ieee80211.c
> index 577dbe3..79c2a60 100644
> --- a/net/mac80211/ieee80211.c
> +++ b/net/mac80211/ieee80211.c
> @@ -54,6 +54,20 @@ static u8 * ieee80211_get_bssid(struct ieee80211_hdr *hdr, size_t len);
>  static int ieee80211_mgmt_start_xmit(struct sk_buff *skb,
>  				     struct net_device *dev);
>  
> +static void ieee80211_include_sequence(struct ieee80211_sub_if_data *sdata,
> +				       struct ieee80211_hdr *hdr)
> +{
> +	/*
> +	 * Set the sequence number for this frame.
> +	 */
> +	hdr->seq_ctrl = cpu_to_le16(sdata->sequence & IEEE80211_SCTL_SEQ);
> +
> +	/*
> +	 * Increase the sequence number.
> +	 */
> +	sdata->sequence = (sdata->sequence + 0x10) & IEEE80211_SCTL_SEQ;
> +}
> +
>  struct ieee80211_key_conf *
>  ieee80211_key_data2conf(struct ieee80211_local *local,
>  			const struct ieee80211_key *data)
> @@ -445,6 +459,7 @@ ieee80211_tx_h_fragment(struct ieee80211_txrx_data *tx)
>  	size_t hdrlen, per_fragm, num_fragm, payload_len, left;
>  	struct sk_buff **frags, *first, *frag;
>  	int i;
> +	u16 seq;
>  	u8 *pos;
>  	int frag_threshold = tx->local->fragmentation_threshold;
>  
> @@ -463,6 +478,7 @@ ieee80211_tx_h_fragment(struct ieee80211_txrx_data *tx)
>  		goto fail;
>  
>  	hdr->frame_control |= cpu_to_le16(IEEE80211_FCTL_MOREFRAGS);
> +	seq = le16_to_cpu(hdr->seq_ctrl) & IEEE80211_SCTL_SEQ;
>  	pos = first->data + hdrlen + per_fragm;
>  	left = payload_len - per_fragm;
>  	for (i = 0; i < num_fragm - 1; i++) {
> @@ -490,7 +506,7 @@ ieee80211_tx_h_fragment(struct ieee80211_txrx_data *tx)
>  		memcpy(fhdr, first->data, hdrlen);
>  		if (i == num_fragm - 2)
>  			fhdr->frame_control &= cpu_to_le16(~IEEE80211_FCTL_MOREFRAGS);
> -		fhdr->seq_ctrl = cpu_to_le16(i + 1);
> +		fhdr->seq_ctrl = cpu_to_le16(seq + ((i + 1) & IEEE80211_SCTL_FRAG));
>  		copylen = left > per_fragm ? per_fragm : left;
>  		memcpy(skb_put(frag, copylen), pos, copylen);
>  
> @@ -900,6 +916,17 @@ ieee80211_tx_h_check_assoc(struct ieee80211_txrx_data *tx)
>  	return TXRX_CONTINUE;
>  }
>  
> +static ieee80211_txrx_result
> +ieee80211_tx_h_sequence(struct ieee80211_txrx_data *tx)
> +{
> +	struct ieee80211_hdr *hdr = (struct ieee80211_hdr *)tx->skb->data;
> +
> +	if ((tx->local->hw.flags & IEEE80211_HW_SOFTWARE_SEQUENCE) &&
> +	    ieee80211_get_hdrlen(le16_to_cpu(hdr->frame_control)) >= 24)
> +		ieee80211_include_sequence(tx->sdata, hdr);
> +
> +	return TXRX_CONTINUE;
> +}
>  
>  /* This function is called whenever the AP is about to exceed the maximum limit
>   * of buffered frames for power saving STAs. This situation should not really
> @@ -1770,6 +1797,10 @@ struct sk_buff * ieee80211_beacon_get(struct ieee80211_hw *hw, int if_id,
>  	skb_reserve(skb, local->hw.extra_tx_headroom);
>  	memcpy(skb_put(skb, bh_len), b_head, bh_len);
>  
> +	if (hw->flags & IEEE80211_HW_SOFTWARE_SEQUENCE)
> +		ieee80211_include_sequence(sdata,
> +			(struct ieee80211_hdr *)skb->data);
> +
>  	ieee80211_beacon_add_tim(local, ap, skb);
>  
>  	if (b_tail) {
> @@ -4381,6 +4412,7 @@ static ieee80211_rx_handler ieee80211_rx_handlers[] =
>  static ieee80211_tx_handler ieee80211_tx_handlers[] =
>  {
>  	ieee80211_tx_h_check_assoc,
> +	ieee80211_tx_h_sequence,
>  	ieee80211_tx_h_ps_buf,
>  	ieee80211_tx_h_select_key,
>  	ieee80211_tx_h_michael_mic_add,
> diff --git a/net/mac80211/ieee80211_i.h b/net/mac80211/ieee80211_i.h
> index 9df8ef0..4b7c427 100644
> --- a/net/mac80211/ieee80211_i.h
> +++ b/net/mac80211/ieee80211_i.h
> @@ -317,6 +317,8 @@ struct ieee80211_sub_if_data {
>  	int ieee802_1x; /* IEEE 802.1X PAE - drop packet to/from unauthorized
>  			 * port */
>  
> +	u16 sequence;
> +
>  	/* Fragment table for host-based reassembly */
>  	struct ieee80211_fragment_entry	fragments[IEEE80211_FRAGMENT_MAX];
>  	unsigned int fragment_next;
> -
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> 

-- 
Greetings Michael.