os_mbuf_prepend

struct os_mbuf *os_mbuf_prepend(struct os_mbuf *om, int len)

Increases the length of an mbuf chain by adding data to the front. If there is insufficient room in the leading mbuf, additional mbufs are allocated and prepended as necessary. If this function fails to allocate an mbuf, the entire chain is freed.

Arguments

Arguments	Description
om	Pointer to mbuf
len	Length, in bytes, to prepend

Returned values

Pointer to mbuf at head of chain; NULL if not enough mbufs were available to accommodate len.

Notes

If om is a packet header mbuf, the total length of the packet is adjusted by len. Note that the returned mbuf may not point to om if insufficient leading space was available in om.

Example

    uint16_t pktlen;
	struct os_mbuf *om;
    struct os_mbuf *tmp;

    /* Get initial packet length before prepend */
    pktlen = OS_MBUF_PKTLEN(om);

    tmp = os_mbuf_prepend(om, 32);
    if (!tmp) {
        /* Not able to prepend. The chain pointed to by *om has been freed */
        return -1;
    }

    /* The packet length should equal the original length plus what we prepended */
    assert((pktlen + 32) == OS_MBUF_PKTLEN(tmp));