os_mbuf_off

struct os_mbuf *os_mbuf_off(struct os_mbuf *om, int off, int *out_off)

Given an offset in the packet (i.e. user data byte offset in the mbuf chain), return the mbuf and the offset in that mbuf where byte ‘off’ is located. Note that the offset is ‘returned’ in out_off.

Arguments

Arguments	Description
om	Pointer to mbuf
off	Location in mbuf chain of desired byte offset
out_off	Pointer to storage for the relative offset of the absolute location in the returned mbuf

Returned values

NULL if the offset is not within the mbuf chain or om points to NULL.

Notes

The user is allowed to call this function with the length of the mbuf chain but no greater. This allows the user to get the mbuf and offset (in that mbuf) where the next user data byte should be written.

While this api is provided to the user, other API are expected to be used by the applciation developer (i.e. os_mbuf_append() or os_mbuf_copyinto()).

Example

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

    /* Append a new line character to end of mbuf data */
    pktlen = OS_MBUF_PKTLEN(om);

    relative_offset = 0;
    tmp = os_mbuf_off(om, pktlen, &relative_offset);
    if (tmp) {
        /* Offset found. */
        tmp->om_data[relative_offset] = '\n';
    } else {
        /*
         * This mbuf does not contain enough bytes so this is an invalid offset.
         * In other words, the mbuf is less than 62 bytes in length.
         */
    }