8.3.4. Control Message Structure
Both Write back & MSI-X completion modes require the application to register event fds for passing number of completed requests. This is done by passing a control message to the driver through read/write system call. To differentiate between a DMA transfer request submission and a control message, the read/write call for the control message must set the count argument to zero.
|uint32_t fefd_tx:1||contains event fd for H2D|
|uint32_t fefd_rx:1||contains event fd for D2H|
|uint32_t reserved:30||reserved for future use|
|int efd_tx;||event fd for H2D|
|int efd_rx;||event fd for D2H|
|int tx_payload;||Payload value of Tx Descriptors|
|int rx_payload;||Payload value of Rx Descriptors|
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