Function ktls_detach_record

freebsd/kern/uipc_ktls.c:1656–1751

}

static struct mbuf *
ktls_detach_record(struct sockbuf *sb, int len)
{
	struct mbuf *m, *n, *top;
	int remain;

	SOCKBUF_LOCK_ASSERT(sb);
	MPASS(len <= sb->sb_tlscc);

	/*
	 * If TLS chain is the exact size of the record,
	 * just grab the whole record.
	 */
	top = sb->sb_mtls;
	if (sb->sb_tlscc == len) {
		sb->sb_mtls = NULL;
		sb->sb_mtlstail = NULL;
		goto out;
	}

	/*
	 * While it would be nice to use m_split() here, we need
	 * to know exactly what m_split() allocates to update the
	 * accounting, so do it inline instead.
	 */
	remain = len;
	for (m = top; remain > m->m_len; m = m->m_next)
		remain -= m->m_len;

	/* Easy case: don't have to split 'm'. */
	if (remain == m->m_len) {
		sb->sb_mtls = m->m_next;
		if (sb->sb_mtls == NULL)
			sb->sb_mtlstail = NULL;
		m->m_next = NULL;
		goto out;
	}

	/*
	 * Need to allocate an mbuf to hold the remainder of 'm'.  Try
	 * with M_NOWAIT first.
	 */
	n = m_get(M_NOWAIT, MT_DATA);
	if (n == NULL) {
		/*
		 * Use M_WAITOK with socket buffer unlocked.  If
		 * 'sb_mtls' changes while the lock is dropped, return
		 * NULL to force the caller to retry.
		 */
		SOCKBUF_UNLOCK(sb);

		n = m_get(M_WAITOK, MT_DATA);

		SOCKBUF_LOCK(sb);
		if (sb->sb_mtls != top) {
			m_free(n);
			return (NULL);
		}