/* Copyright (c) 2013-2017, The Linux Foundation. All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 and
 * only version 2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * RMNET Data MAP protocol
 *
 */

#include <linux/netdevice.h>
#include "rmnet_config.h"
#include "rmnet_map.h"
#include "rmnet_private.h"

#define RMNET_MAP_DEAGGR_SPACING  64
#define RMNET_MAP_DEAGGR_HEADROOM (RMNET_MAP_DEAGGR_SPACING / 2)

/* Adds MAP header to front of skb->data
 * Padding is calculated and set appropriately in MAP header. Mux ID is
 * initialized to 0.
 */
struct rmnet_map_header *rmnet_map_add_map_header(struct sk_buff *skb,
						  int hdrlen, int pad)
{
	struct rmnet_map_header *map_header;
	u32 padding, map_datalen;
	u8 *padbytes;

	if (skb_headroom(skb) < sizeof(struct rmnet_map_header))
		return NULL;

	map_datalen = skb->len - hdrlen;
	map_header = (struct rmnet_map_header *)
			skb_push(skb, sizeof(struct rmnet_map_header));
	memset(map_header, 0, sizeof(struct rmnet_map_header));

	if (pad == RMNET_MAP_NO_PAD_BYTES) {
		map_header->pkt_len = htons(map_datalen);
		return map_header;
	}

	padding = ALIGN(map_datalen, 4) - map_datalen;

	if (padding == 0)
		goto done;

	if (skb_tailroom(skb) < padding)
		return NULL;

	padbytes = (u8 *)skb_put(skb, padding);
	memset(padbytes, 0, padding);

done:
	map_header->pkt_len = htons(map_datalen + padding);
	map_header->pad_len = padding & 0x3F;

	return map_header;
}

/* Deaggregates a single packet
 * A whole new buffer is allocated for each portion of an aggregated frame.
 * Caller should keep calling deaggregate() on the source skb until 0 is
 * returned, indicating that there are no more packets to deaggregate. Caller
 * is responsible for freeing the original skb.
 */
struct sk_buff *rmnet_map_deaggregate(struct sk_buff *skb)
{
	struct rmnet_map_header *maph;
	struct sk_buff *skbn;
	u32 packet_len;

	if (skb->len == 0)
		return NULL;

	maph = (struct rmnet_map_header *)skb->data;
	packet_len = ntohs(maph->pkt_len) + sizeof(struct rmnet_map_header);

	if (((int)skb->len - (int)packet_len) < 0)
		return NULL;

	/* Some hardware can send us empty frames. Catch them */
	if (ntohs(maph->pkt_len) == 0)
		return NULL;

	skbn = alloc_skb(packet_len + RMNET_MAP_DEAGGR_SPACING, GFP_ATOMIC);
	if (!skbn)
		return NULL;

	skbn->dev = skb->dev;
	skb_reserve(skbn, RMNET_MAP_DEAGGR_HEADROOM);
	skb_put(skbn, packet_len);
	memcpy(skbn->data, skb->data, packet_len);
	skb_pull(skb, packet_len);

	return skbn;
}