Zero-Copy

xgl_send_zerocopy() is designed for single-frame, unreliable sends using caller-owned writable buffers.

Supported Scope

• True zero-copy: single-frame unreliable send.
• Reliable zero-copy: rejected with XGL_ERR_INVALID_PARAM; use xgl_send() when ACK/retry semantics are required.

Buffer Requirements

• Buffer must be writable.
• Payload must reserve space for header and required extensions.
• When auth_required is true, reserve SECURITY_EXT and authentication trailer space.
• Route MTU must fit the final frame.

Offset Rules

Unauthenticated single-frame sends place payload at XGL_FRAME_HEADER_SIZE when data_type == 0. When data_type != 0, reserve DATA_TYPE_EXT as well, so the offset is XGL_FRAME_HEADER_SIZE + XGL_DATA_TYPE_EXT_SIZE. Authenticated paths also reserve SECURITY_EXT, adding 15 bytes. Do not write magic or CRC manually; let the protocol stack fill them.

Ownership

The caller buffer must remain valid until the PHY TX callback returns. The zero-copy path bypasses transport and network send processing, then updates their TX statistics explicitly after the raw datalink send succeeds.

Common Misuse

• No header reservation.
• Provider has no tag length while authentication is required.
• Passing reliable data to xgl_send_zerocopy() instead of using xgl_send().