`npkt_t`

Main data structure for a packet

Synopsis:

typedef struct _npkt {
    TAILQ_HEAD(, _net_buf) buffers;
    npkt_t       *next;
    void         *io_net0;
    void         *org_data;
    uint32_t     flags;
    uint32_t     framelen;
    uint32_t     tot_iov;
    uint32_t     io_net1;
    uint32_t     ref_cnt;
    uint16_t     num_complete;
    uint16_t     req_complete;
    uint16_t     cell;
    uint16_t     endpoint;
    uint16_t     iface;
    uint16_t     skip;
    union {
        void     *p;
        unsigned char c [16];
    } inter_module;
} npkt_t;

// This field follows the structure implicitly:

npkt_done_t  c [];

Description:

The npkt_t structure is the main data structure for a packet. The fields include:

buffers

A queue of buffers, managed using the TAILQ*() macros from <sys/queue.h>.

next

A pointer to the next npkt_t. Modules can use this pointer to queue packets.

io_net0, io_net1, ref_cnt

Internal to io-net, don't examine or modify.

org_data

For the exclusive use of the originator of this npkt_t. No one else should touch this member.

flags

The status of the buffer. This is a combination of the following bits:

_NPKT_NOT_TXED -- the packet hasn't actually been transmitted.
_NPKT_NO_RES -- the up producer that originated the packet wants its buffer back right away. If the up producer that originates the packet sets this flag, the up producer's tx_done() function is guaranteed to be called by the time io-net's tx_done() has returned. The implication is that the up producer can reuse the buffer right away. It's more efficient not to set this flag.
_NPKT_UP -- the npkt_t is headed in the up direction; down if this bit isn't set.
_NPKT_MSG -- this message is intended for a different layer, rather than actually containing packet data.
_NPKT_MSG_DYING -- when a driver is unmounted, io-net synthesizes a npkt_t structure with the flags set to _NPKT_MSG | _NPKT_MSG_DYING, and sends it up as though it came from the driver. It has no data in it. It means this cell, endpoint, and all ifaces are gone.
_NPKT_BCAST -- a broadcast packet.
_NPKT_MCAST -- a multicast packet.
_NPKT_INTERNAL -- internal to io-net.

The originator of the packet can use the top 12 bits as it sees fit. _NPKT_ORG_MASK is a mask that you can use to get just these bits.

framelen

The total length of the entire packet.

tot_iov

The total number of iovs in the packet.

num_complete

The number of elements in the npkt_done_t array that implicitly immediately follows this structure.

req_complete

The required number of npkt_done_t elements this downward-headed packet required before it reached its final destination. This member is for information purposes only (read-only) in the originator's tx_done() function if the originator isn't using io-net's alloc_down_pkt() function.

cell

The cell to or from which the npkt_t is headed.

endpoint

The endpoint within the cell.

iface

The interface within the endpoint.

skip

For use by _REG_FILTER_BELOW types of modules. The idea is that they can receive a packet from above, modify it somehow, stuff their reg_hdl in the skip member, and return TX_DOWN_AGAIN (from <sys/io-net.h>) from their rx_down() function. The down producer sees TX_DOWN_AGAIN and resends it down (after recalculating the checksum, rerouting, etc.), but this time, the _REG_FILTER_BELOW is skipped by io-net. The down producer has to support the TX_DOWN_AGAIN return code.

inter_module.p, inter_module.c

A data area that can be used by any module to pass information to the module above or below it.

The npkt_t is implicitly followed immediately by an array, c, of npkt_done_t structures. On a downward-headed transmission, this array is num_complete elements long, whereas on an upward-headed transmission, it's always 1 element long.

Classification:

QNX