GLDv3 Capabilities

GLDv3 implements a capability mechanism that allows the framework to query and enable capabilities that are supported by the GLDv3 driver. Use the mc_getcapab(9E)entry point to report capabilities. If a capability is supported by the driver, pass information about that capability, such as capability-specific entry points or flags through mc_getcapab(). Pass a pointer to the mc_getcapab() entry point in the mac_callback structure. See GLDv3 MAC Registration Data Structures for more information about the mac_callbacks structure.

boolean_t mc_getcapab(void *driver_handle, mac_capab_t cap, void *cap_data);

The cap argument specifies the type of capability being queried. The value of cap can be either MAC_CAPAB_HCKSUM (hardware checksum offload) or MAC_CAPAB_LSO (large segment offload). Use the cap_data argument to return the capability data to the framework.

If the driver supports the cap capability, the mc_getcapab() entry point must return B_TRUE. If the driver does not support the cap capability, mc_getcapab() must return B_FALSE.

Example 19–5 The mc_getcapab() Entry Point

static boolean_t
xx_m_getcapab(void *arg, mac_capab_t cap, void *cap_data)
{
        switch (cap) {
        case MAC_CAPAB_HCKSUM: {
                uint32_t *txflags = cap_data;
                *txflags = HCKSUM_INET_FULL_V4 | HCKSUM_IPHDRCKSUM;
                break;
        }
        case MAC_CAPAB_LSO: {
                /* ... */
                break;
        }
        default:
                return (B_FALSE);
        }
        return (B_TRUE);
}

The following sections describe the supported capabilities and the corresponding capability data to return.

Hardware Checksum Offload

To get data about support for hardware checksum offload, the framework sends MAC_CAPAB_HCKSUM in the cap argument. See Hardware Checksum Offload Capability Information.

To query checksum offload metadata and retrieve the per-packet hardware checksumming metadata when hardware checksumming is enabled, use mac_hcksum_get(9F). See The mac_hcksum_get() Function Flags.

To set checksum offload metadata, use mac_hcksum_set(9F). See The mac_hcksum_set() Function Flags.

See Hardware Checksumming: Hardware and Hardware Checksumming: MAC Layer for more information.

Hardware Checksum Offload Capability Information

To pass information about the MAC_CAPAB_HCKSUM capability to the framework, the driver must set a combination of the following flags in cap_data, which points to a uint32_t. These flags indicate the level of hardware checksum offload that the driver is capable of performing for outbound packets.

HCKSUM_INET_PARTIAL

Partial 1's complement checksum ability

HCKSUM_INET_FULL_V4

Full 1's complement checksum ability for IPv4 packets

HCKSUM_INET_FULL_V6

Full 1's complement checksum ability for IPv6 packets

HCKSUM_IPHDRCKSUM

IPv4 Header checksum offload capability

The mac_hcksum_get() Function Flags

The flags argument of mac_hcksum_get() is a combination of the following values:

HCK_FULLCKSUM

Compute the full checksum for this packet.

HCK_FULLCKSUM_OK

The full checksum was verified in hardware and is correct.

HCK_PARTIALCKSUM

Compute the partial 1's complement checksum based on other parameters passed to mac_hcksum_get(). HCK_PARTIALCKSUM is mutually exclusive with HCK_FULLCKSUM.

HCK_IPV4_HDRCKSUM

Compute the IP header checksum.

HCK_IPV4_HDRCKSUM_OK

The IP header checksum was verified in hardware and is correct.

The mac_hcksum_set() Function Flags

The flags argument of mac_hcksum_set() is a combination of the following values:

HCK_FULLCKSUM

The full checksum was computed and passed through the value argument.

HCK_FULLCKSUM_OK

The full checksum was verified in hardware and is correct.

HCK_PARTIALCKSUM

The partial checksum was computed and passed through the value argument. HCK_PARTIALCKSUM is mutually exclusive with HCK_FULLCKSUM.

HCK_IPV4_HDRCKSUM

The IP header checksum was computed and passed through the value argument.

HCK_IPV4_HDRCKSUM_OK

The IP header checksum was verified in hardware and is correct.

Large Segment (or Send) Offload

To query support for large segment (or send) offload, the framework sends MAC_CAPAB_LSO in the cap argument and expects the information back in cap_data, which points to a mac_capab_lso(9S) structure. The framework allocates the mac_capab_lso structure and passes a pointer to this structure in cap_data. The mac_capab_lso structure consists of an lso_basic_tcp_ipv4(9S) structure and an lso_flags member. If the driver instance supports LSO for TCP on IPv4, set the LSO_TX_BASIC_TCP_IPV4 flag in lso_flags and set the lso_max member of the lso_basic_tcp_ipv4 structure to the maximum payload size supported by the driver instance.

Use mac_lso_get(9F) to obtain per-packet LSO metadata. If LSO is enabled for this packet, the HW_LSO flag is set in the mac_lso_get() flags argument. The maximum segment size (MSS) to be used during segmentation of the large segment is returned through the location pointed to by the mss argument. See Large Segment Offload for more information.