struct os_mbuf *os_mbuf_pullup(struct os_mbuf *om, uint16_t len)
Rearrange an mbuf chain so that len bytes are contiguous, and in the data area of an mbuf (so that OS_MBUF_DATA() will work on a structure of size len.) Returns the resulting mbuf chain on success, free's it and returns NULL on failure.
| Arguments | Description |
|---|---|
| om | Pointer to mbuf |
| len | Length, in bytes, to pullup (make contiguous in mbuf) |
Pointer to mbuf at head of chain; NULL if not enough mbufs were available to accommodate len or if the requested pullup size was too large.
Hopefully it is apparent to the user that you cannot pullup more bytes than the mbuf can accommodate. Pullup does not allocate more than one mbuf; the entire pullup length must be contained within a single mbuf.
The mbuf that is being pulled up into does not need to be a packet header mbuf; it can be a normal mbuf. The user should note that the maximum pullup length does depend on the type of mbuf being pulled up into (a packet header or normal mbuf).
struct os_mbuf *om; struct os_mbuf *tmp; struct my_header_struct my_header; /* Make sure "my_header" is contiguous in the mbuf */ tmp = os_mbuf_pullup(om, sizeof(my_header_struct)); if (!tmp) { /* Pullup failed. The chain pointed to by *om has been freed */ return -1; } /* copy data from mbuf into header structure */ memcpy(&my_header, tmp->om_data, sizeof(struct my_header_struct));