[OMPI devel] mca_btl_tcp_alloc

[Alex Margolin]

Hi,

As I'm working out the bugs in my component I used TCP as reference and 
came across the following:
In mca_btl_tcp_alloc (openmpi-trunk/ompi/mca/btl/tcp/btl_tcp.c:188) the 
first segment is initialized to point to "frag + 1".
I don't get it... how/when is this location allocated? Isn't it just 
after the mca_btl_tcp_frag_t structure ends?

Thanks,
Alex

mca_btl_base_descriptor_t* mca_btl_tcp_alloc(
    struct mca_btl_base_module_t* btl,
    struct mca_btl_base_endpoint_t* endpoint,
    uint8_t order,
    size_t size,
    uint32_t flags)
{
    mca_btl_tcp_frag_t* frag = NULL;
    int rc;

    if(size <= btl->btl_eager_limit) {
        MCA_BTL_TCP_FRAG_ALLOC_EAGER(frag, rc);
    } else if (size <= btl->btl_max_send_size) {
        MCA_BTL_TCP_FRAG_ALLOC_MAX(frag, rc);
    }
    if( OPAL_UNLIKELY(NULL == frag) ) {
        return NULL;
    }

    frag->segments[0].seg_len = size;
    frag->segments[0].seg_addr.pval = frag+1;

    frag->base.des_src = frag->segments;
    frag->base.des_src_cnt = 1;
    frag->base.des_dst = NULL;
    frag->base.des_dst_cnt = 0;
    frag->base.des_flags = flags;
    frag->base.order = MCA_BTL_NO_ORDER;
    frag->btl = (mca_btl_tcp_module_t*)btl;
    return (mca_btl_base_descriptor_t*)frag;
}