Creating a UD address handle from user-space or from the kernel-space,
when the link layer is ethernet, requires resolving the remote L3
address into a L2 address. Doing this from the kernel is easy because
the required ARP(IPv4) and ND6(IPv6) address resolving APIs are readily
available. In userspace such an interface does not exist and kernel
help is required.
It should be noted that in an IP-based GID environment, the GID itself
does not contain all the information needed to resolve the destination
IP address. For example information like VLAN ID and SCOPE ID, is not
part of the GID and must be fetched from the GID attributes. Therefore
a source GID should always be referred to as a GID index. Instead of
going through various racy steps to obtain information about the
GID attributes from user-space, this is now all done by the kernel.
This patch optimises the L3 to L2 address resolving using the existing
create address handle uverbs interface, retrieving back the L2 address
as an additional user-space information structure.
This commit combines the following Linux upstream commits:
IB/core: Let create_ah return extended response to user
IB/core: Change ib_resolve_eth_dmac to use it in create AH
IB/mlx5: Make create/destroy_ah available to userspace
IB/mlx5: Use kernel driver to help userspace create ah
IB/mlx5: Report that device has udata response in create_ah
MFC after: 1 week
Sponsored by: Mellanox Technologies
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