mmap() returns with -EINVAL

[leo mueller <llug.dan@googlemail.com>]

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hi all,

in my attached code snippet i try to mmap the incoming socket data
accoring to the kernel documentation
which can also be found online:
http://lxr.linux.no/linux+v2.6.30/Documentation/networking/packet_mmap.txt

by doing a mmap() my program exits with -EINVAL and up to now i have
no clue why... parametes should be right.

do you have any idea?

big thanks,
daniel

[-- Attachment #2: err.txt --]
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typedef unsigned char *ring_buff_t;

[...]

ring_buff_t create_virt_ring(int sock)
{
    int ret;
    ring_buff_t rb;
    struct tpacket_req req;

    memset(&req, 0, sizeof(req));

    dbg("pagesize: %d\n", getpagesize());

    req.tp_block_size = getpagesize();
    req.tp_frame_size = TP_RX_FRAME_SIZ;
    req.tp_block_nr = TP_RX_BLOCKS;
    req.tp_frame_nr = req.tp_block_size / req.tp_frame_size * req.tp_block_nr;

    ret = setsockopt(sock, SOL_SOCKET, PACKET_RX_RING, (void *) &req, sizeof(req));
    if(ret < 0){
        err("setsockopt: creation of rx ring failed: %d - ", errno);
        perror("");
        goto _out_err;
    }

    rb = mmap(0, (size_t) req.tp_block_nr * req.tp_block_size, PROT_READ | PROT_WRITE, MAP_SHARED, sock, 0);
    if(rb == MAP_FAILED){
        err("mmap: cannot mmap the rx ring: %d - ", errno);
        perror("");
        goto _out_mmap;
    }

    dbg("kernel ringbuff allocated\n");

    return rb;

_out_mmap:
    destroy_virt_ring(sock, rb);
_out_err:
    close(sock);
    exit(1);
}

[...]

void destroy_virt_ring(int sock, ring_buff_t rb)
{
    int ret;
    struct tpacket_req req;

    memset(&req, 0, sizeof(req));
    ret = setsockopt(sock, SOL_PACKET, PACKET_RX_RING, (void *) &req, sizeof(req));
    if(ret < 0){
        err("setsockopt: destruction of rx ring failed: %d - ", errno);
        perror("");
    }

	if(rb){
        munmap(rb, TP_RX_BLOCKS * getpagesize());
        rb = 0;
    }
    
    dbg("kernel ringbuff deallocated\n");
}