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fi_usnic - Man Page

The usNIC Fabric Provider


The usnic provider is designed to run over the Cisco VIC (virtualized NIC) hardware on Cisco UCS servers. It utilizes the Cisco usNIC (userspace NIC) capabilities of the VIC to enable ultra low latency and other offload capabilities on Ethernet networks.

Release Notes

Usnic Extensions

The usnic libfabric provider exports extensions for additional VIC, usNIC, and Ethernet capabilities not provided by the standard libfabric interface.

These extensions are available via the “fi_ext_usnic.h” header file.

Fabric Extension: getinfo

Version 2 of the “fabric getinfo” extension was introduced in Libfabric release v1.3.0 and can be used to retrieve IP and SR-IOV information about a usNIC device obtained from the fi_getinfo(3) function.

The “fabric getinfo” extension is obtained by calling fi_open_ops and requesting FI_USNIC_FABRIC_OPS_1 to get the usNIC fabric extension operations. The getinfo function accepts a version parameter that can be used to select different versions of the extension. The information returned by the “fabric getinfo” extension is accessible through a fi_usnic_info struct that uses a version tagged union. The accessed union member must correspond with the requested version. It is recommended that applications explicitly request a version rather than using the header provided FI_EXT_USNIC_INFO_VERSION. Although there is a version 1 of the extension, its use is discouraged, and it may not be available in future releases.

Compatibility issues

The addition of version 2 of the extension caused an alignment issue that could lead to invalid data in the v1 portion of the structure. This means that the alignment difference manifests when an application using v1 of the extension is compiled with Libfabric v1.1.x or v1.2.x, but then runs with Libfabric.so that is v1.3.x or higher (and vice versa).

The v1.4.0 release of Libfabric introduced a padding field to explicitly maintain compatibility with the v1.3.0 release. If the issue is encountered, then it is recommended that you upgrade to a release containing version 2 of the extension, or recompile with a patched version of an older release.

#include <rdma/fi_ext_usnic.h>

struct fi_usnic_info {
    uint32_t ui_version;
    uint8_t ui_pad0[4];
    union {
        struct fi_usnic_info_v1 v1;
        struct fi_usnic_info_v2 v2;
    } ui;
} __attribute__((packed));

int getinfo(uint32_t version, struct fid_fabric *fabric,
        struct fi_usnic_info *info);

Version of getinfo to be used


Fabric descriptor


Upon successful return, this parameter will contain information about the fabric.


Version 2

struct fi_usnic_cap {
    const char *uc_capability;
    int uc_present;
} __attribute__((packed));

struct fi_usnic_info_v2 {
    uint32_t        ui_link_speed;
    uint32_t        ui_netmask_be;
    char            ui_ifname[IFNAMSIZ];
    unsigned        ui_num_vf;
    unsigned        ui_qp_per_vf;
    unsigned        ui_cq_per_vf;

    char            ui_devname[FI_EXT_USNIC_MAX_DEVNAME];
    uint8_t         ui_mac_addr[6];

    uint8_t         ui_pad0[2];

    uint32_t        ui_ipaddr_be;
    uint32_t        ui_prefixlen;
    uint32_t        ui_mtu;
    uint8_t         ui_link_up;

    uint8_t         ui_pad1[3];

    uint32_t        ui_vendor_id;
    uint32_t        ui_vendor_part_id;
    uint32_t        ui_device_id;
    char            ui_firmware[64];

    unsigned        ui_intr_per_vf;
    unsigned        ui_max_cq;
    unsigned        ui_max_qp;

    unsigned        ui_max_cqe;
    unsigned        ui_max_send_credits;
    unsigned        ui_max_recv_credits;

    const char      *ui_nicname;
    const char      *ui_pid;

    struct fi_usnic_cap **ui_caps;
} __attribute__((packed));

Version 1

struct fi_usnic_info_v1 {
    uint32_t ui_link_speed;
    uint32_t ui_netmask_be;
    char ui_ifname[IFNAMSIZ];

    uint32_t ui_num_vf;
    uint32_t ui_qp_per_vf;
    uint32_t ui_cq_per_vf;
} __attribute__((packed));

Version 1 of the “fabric getinfo” extension can be used by explicitly requesting it in the call to getinfo and accessing the v1 portion of the fi_usnic_info.ui union. Use of version 1 is not recommended and it may be removed from future releases.

The following is an example of how to utilize version 2 of the usnic “fabric getinfo” extension.

#include <stdio.h>
#include <rdma/fabric.h>

/* The usNIC extensions are all in the
   rdma/fi_ext_usnic.h header */
#include <rdma/fi_ext_usnic.h>

int main(int argc, char *argv[]) {
    struct fi_info *info;
    struct fi_info *info_list;
    struct fi_info hints = {0};
    struct fi_ep_attr ep_attr = {0};
    struct fi_fabric_attr fabric_attr = {0};

    fabric_attr.prov_name = "usnic";
    ep_attr.type = FI_EP_DGRAM;

    hints.caps = FI_MSG;
    hints.mode = FI_LOCAL_MR | FI_MSG_PREFIX;
    hints.addr_format = FI_SOCKADDR;
    hints.ep_attr = &ep_attr;
    hints.fabric_attr = &fabric_attr;

    /* Find all usnic providers */
    fi_getinfo(FI_VERSION(1, 0), NULL, 0, 0, &hints, &info_list);

    for (info = info_list; NULL != info; info = info->next) {
        /* Open the fabric on the interface */
        struct fid_fabric *fabric;
        fi_fabric(info->fabric_attr, &fabric, NULL);

        /* Pass FI_USNIC_FABRIC_OPS_1 to get usnic ops
           on the fabric */
        struct fi_usnic_ops_fabric *usnic_fabric_ops;
        fi_open_ops(&fabric->fid, FI_USNIC_FABRIC_OPS_1, 0,
                (void **) &usnic_fabric_ops, NULL);

        /* Now use the returned usnic ops structure to call
           usnic extensions.  The following extension queries
           some IP and SR-IOV characteristics about the
           usNIC device. */
        struct fi_usnic_info usnic_info;

        /* Explicitly request version 2. */
        usnic_fabric_ops->getinfo(2, fabric, &usnic_info);

        printf("Fabric interface %s is %s:\n"
               "\tNetmask:  0x%08x\n\tLink speed: %d\n"
               "\tSR-IOV VFs: %d\n\tQPs per SR-IOV VF: %d\n"
               "\tCQs per SR-IOV VF: %d\n",


    return 0;

Adress Vector Extension: get_distance

The “address vector get_distance” extension was introduced in Libfabric release v1.0.0 and can be used to retrieve the network distance of an address.

The “get_distance” extension is obtained by calling fi_open_ops and requesting FI_USNIC_AV_OPS_1 to get the usNIC address vector extension operations.

int get_distance(struct fid_av *av, void *addr, int *metric);

Address vector


Destination address


On output this will contain -1 if the destination host is unreachable, 0 is the destination host is locally connected, and 1 otherwise.

See fi_ext_usnic.h for more details.

Version Differences

New naming convention for fabric/domain starting with libfabric v1.4

The release of libfabric v1.4 introduced a new naming convention for fabric and domain. However the usNIC provider remains backward compatible with applications supporting the old scheme and decides which one to use based on the version passed to fi_getinfo:

  • When FI_VERSION(1,4) or higher is used:

    • fabric name is the network address with the CIDR notation (i.e., a.b.c.d/e)
    • domain name is the usNIC Linux interface name (i.e., usnic_X)
  • When a lower version number is used, like FI_VERSION(1, 3), it follows the same behavior the usNIC provider exhibited in libfabric <= v1.3:

    • fabric name is the usNIC Linux interface name (i.e., usnic_X)
    • domain name is NULL

See Also

fabric(7), fi_open_ops(3), fi_provider(7),




2022-12-09 Libfabric Programmer’s Manual Libfabric v1.21.0