if ((seg->p = pbuf_alloc(PBUF_TRANSPORT, optlen, PBUF_RAM)) == NULL) {
goto memerr;
}
++queuelen;
seg->dataptr = seg->p->payload;
}
/* copy from volatile memory? */
else if (copy) { /* 分配一个 RAM 类型的 pbuf，将待发送数据拷贝进去 */
if ((seg->p = pbuf_alloc(PBUF_TRANSPORT, seglen, PBUF_RAM)) == NULL) {
......
goto memerr;
}
++queuelen;
if (arg != NULL) {
memcpy(seg->p->payload, ptr, seglen);
}
seg->dataptr = seg->p->payload;
}
/* do not copy data */
else {
/* First, allocate a pbuf for holding the data.
* since the referenced data is available at least until it is sent out on the
* link (as it has to be ACKed by the remote party) we can safely use PBUF_ROM
* instead of PBUF_REF here. */
if ((p = pbuf_alloc(PBUF_TRANSPORT, seglen, PBUF_ROM)) == NULL) {
......
goto memerr;
}
++queuelen;
/* reference the non-volatile payload data */
p->payload = ptr;
seg->dataptr = ptr;
/* Second, allocate a pbuf for the headers. */
if ((seg->p = pbuf_alloc(PBUF_TRANSPORT, 0, PBUF_RAM)) == NULL) {
/* If allocation fails, we have to deallocate the data pbuf as
* well. */
pbuf_free(p);
......
goto memerr;
}
++queuelen;
/* Concatenate the headers and data pbufs together. */
pbuf_cat(seg->p/*header*/, p/*data*/);
p = NULL;
}
/* 此时，已分配一个 segment，并关联上了一个 pbuf或 pbuf chain */
/* Now that there are more segments queued, we check again if the
length of the queue exceeds the configured maximum. */
if (queuelen > TCP_SND_QUEUELEN) {
......
goto memerr;
}
seg->len = seglen;
/* build TCP header */
if (pbuf_header(seg->p, TCP_HLEN)) {
......
goto memerr;
}
seg->tcphdr = seg->p->payload;
seg->tcphdr->src = htons(pcb->local_port);
seg->tcphdr->dest = htons(pcb->remote_port);
seg->tcphdr->seqno = htonl(seqno);
seg->tcphdr->urgp = 0;
TCPH_FLAGS_SET(seg->tcphdr, flags);
/* don't fill in tcphdr->ackno and tcphdr->wnd until later */ /* 到真正发送时再填写 */
/* Copy the options into the header, if they are present. */
if (optdata == NULL) {
TCPH_HDRLEN_SET(seg->tcphdr, 5);
}
else {
TCPH_HDRLEN_SET(seg->tcphdr, (5 + optlen / 4));
/* Copy options into data portion of segment.
Options can thus only be sent in non data carrying
segments such as SYN|ACK. */
memcpy(seg->dataptr, optdata, optlen);
}
......
left -= seglen;
seqno += seglen;
ptr = (void *)((u8_t *)ptr + seglen);
} |
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