[lwip-devel] Odd check in pbuf_alloced_custom (typo?)

[Mason]

Hello,

My calls to pbuf_alloced_custom() are failing, and I don't
understand the logic for the failure.

pbuf_alloced_custom is documented the following way:

/** Initialize a custom pbuf (already allocated).
 *
 * @param layer flag to define header size
 * @param length size of the pbuf's payload
 * @param type type of the pbuf (only used to treat the pbuf accordingly, as
 *        this function allocates no memory)
 * @param p pointer to the custom pbuf to initialize (already allocated)
 * @param payload_mem pointer to the buffer that is used for payload and 
headers,
 *        must be at least big enough to hold 'length' plus the header size,
 *        may be NULL if set later
 * @param payload_mem_len the size of the 'payload_mem' buffer, must be at least
 *        big enough to hold 'length' plus the header size
 */
struct pbuf *pbuf_alloced_custom(
  pbuf_layer l,
  u16_t length,
  pbuf_type type,
  struct pbuf_custom *p,
  void *payload_mem,
  u16_t payload_mem_len)

If I understand correctly, 'payload_mem' points to a buffer which can
store 'payload_mem_len' octets; length is the ACTUAL size of the
payload.

Thus (please correct me if I am mistaken) supposing I have allocated
1600 octets for a buffer, and I have received an Ethernet frame that
is 120-octets long, then

  length = 120 and payload_mem_len = 1600

correct?

However, pbuf_alloced_custom performs the following check:

if (LWIP_MEM_ALIGN_SIZE(offset) + length < payload_mem_len)
{
  /*** ERROR ***/
}

which seems to be the opposite of what the comments (and logic)
suggest.

If payload_mem_len "must be at least big enough to hold 'length'
plus the header size", then there is an error when

LWIP_MEM_ALIGN_SIZE(offset) + length > payload_mem_len

Is this just a typo, with the comparison operator reversed?
Or am I completely misunderstanding the logic of the code?

-- 
Regards.