diff --git a/include/uapi/linux/homa.h b/include/uapi/linux/homa.h
new file mode 100644
index 000000000000..306d272e4b63
--- /dev/null
+++ b/include/uapi/linux/homa.h
@@ -0,0 +1,199 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+
+/* This file defines the kernel call interface for the Homa
+ * transport protocol.
+ */
+
+#ifndef _UAPI_LINUX_HOMA_H
+#define _UAPI_LINUX_HOMA_H
+
+#include <linux/types.h>
+#ifndef __KERNEL__
+#include <netinet/in.h>
+#include <sys/socket.h>
+#endif
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+/* IANA-assigned Internet Protocol number for Homa. */
+#define IPPROTO_HOMA 146
+
+/**
+ * define HOMA_MAX_MESSAGE_LENGTH - Maximum bytes of payload in a Homa
+ * request or response message.
+ */
+#define HOMA_MAX_MESSAGE_LENGTH 1000000
+
+/**
+ * define HOMA_BPAGE_SIZE - Number of bytes in pages used for receive
+ * buffers. Must be power of two.
+ */
+#define HOMA_BPAGE_SHIFT 16
+#define HOMA_BPAGE_SIZE (1 << HOMA_BPAGE_SHIFT)
+
+/**
+ * define HOMA_MAX_BPAGES: The largest number of bpages that will be required
+ * to store an incoming message.
+ */
+#define HOMA_MAX_BPAGES ((HOMA_MAX_MESSAGE_LENGTH + HOMA_BPAGE_SIZE - 1) \
+		>> HOMA_BPAGE_SHIFT)
+
+/**
+ * define HOMA_MIN_DEFAULT_PORT - The 16-bit port space is divided into
+ * two nonoverlapping regions. Ports 1-32767 are reserved exclusively
+ * for well-defined server ports. The remaining ports are used for client
+ * ports; these are allocated automatically by Homa. Port 0 is reserved.
+ */
+#define HOMA_MIN_DEFAULT_PORT 0x8000
+
+/**
+ * Holds either an IPv4 or IPv6 address (smaller and easier to use than
+ * sockaddr_storage).
+ */
+union sockaddr_in_union {
+	struct sockaddr sa;
+	struct sockaddr_in in4;
+	struct sockaddr_in6 in6;
+};
+
+/**
+ * struct homa_sendmsg_args - Provides information needed by Homa's
+ * sendmsg; passed to sendmsg using the msg_control field.
+ */
+struct homa_sendmsg_args {
+	/**
+	 * @id: (in/out) An initial value of 0 means a new request is
+	 * being sent; nonzero means the message is a reply to the given
+	 * id. If the message is a request, then the value is modified to
+	 * hold the id of the new RPC.
+	 */
+	uint64_t id;
+
+	/**
+	 * @completion_cookie: (in) Used only for request messages; will be
+	 * returned by recvmsg when the RPC completes. Typically used to
+	 * locate app-specific info about the RPC.
+	 */
+	uint64_t completion_cookie;
+};
+
+#if !defined(__cplusplus)
+_Static_assert(sizeof(struct homa_sendmsg_args) >= 16,
+	       "homa_sendmsg_args shrunk");
+_Static_assert(sizeof(struct homa_sendmsg_args) <= 16,
+	       "homa_sendmsg_args grew");
+#endif
+
+/**
+ * struct homa_recvmsg_args - Provides information needed by Homa's
+ * recvmsg; passed to recvmsg using the msg_control field.
+ */
+struct homa_recvmsg_args {
+	/**
+	 * @id: (in/out) Initially specifies the id of the desired RPC, or 0
+	 * if any RPC is OK; returns the actual id received.
+	 */
+	uint64_t id;
+
+	/**
+	 * @completion_cookie: (out) If the incoming message is a response,
+	 * this will return the completion cookie specified when the
+	 * request was sent. For requests this will always be zero.
+	 */
+	uint64_t completion_cookie;
+
+	/**
+	 * @flags: (in) OR-ed combination of bits that control the operation.
+	 * See below for values.
+	 */
+	int flags;
+
+	/**
+	 * @error_addr: the address of the peer is stored here when available.
+	 * This field is different from the msg_name field in struct msghdr
+	 * in that the msg_name field isn't set after errors. This field will
+	 * always be set when peer information is available, which includes
+	 * some error cases.
+	 */
+	union sockaddr_in_union peer_addr;
+
+	/**
+	 * @num_bpages: (in/out) Number of valid entries in @bpage_offsets.
+	 * Passes in bpages from previous messages that can now be
+	 * recycled; returns bpages from the new message.
+	 */
+	uint32_t num_bpages;
+
+	uint32_t _pad[1];
+
+	/**
+	 * @bpage_offsets: (in/out) Each entry is an offset into the buffer
+	 * region for the socket pool. When returned from recvmsg, the
+	 * offsets indicate where fragments of the new message are stored. All
+	 * entries but the last refer to full buffer pages (HOMA_BPAGE_SIZE bytes)
+	 * and are bpage-aligned. The last entry may refer to a bpage fragment and
+	 * is not necessarily aligned. The application now owns these bpages and
+	 * must eventually return them to Homa, using bpage_offsets in a future
+	 * recvmsg invocation.
+	 */
+	uint32_t bpage_offsets[HOMA_MAX_BPAGES];
+};
+
+#if !defined(__cplusplus)
+_Static_assert(sizeof(struct homa_recvmsg_args) >= 120,
+	       "homa_recvmsg_args shrunk");
+_Static_assert(sizeof(struct homa_recvmsg_args) <= 120,
+	       "homa_recvmsg_args grew");
+#endif
+
+/* Flag bits for homa_recvmsg_args.flags (see man page for documentation):
+ */
+#define HOMA_RECVMSG_REQUEST       0x01
+#define HOMA_RECVMSG_RESPONSE      0x02
+#define HOMA_RECVMSG_NONBLOCKING   0x04
+#define HOMA_RECVMSG_VALID_FLAGS   0x07
+
+/** define SO_HOMA_SET_BUF: setsockopt option for specifying buffer region. */
+#define SO_HOMA_SET_BUF 10
+
+/** struct homa_set_buf - setsockopt argument for SO_HOMA_SET_BUF. */
+struct homa_set_buf_args {
+	/** @start: First byte of buffer region. */
+	void *start;
+
+	/** @length: Total number of bytes available at @start. */
+	size_t length;
+};
+
+/**
+ * Meanings of the bits in Homa's flag word, which can be set using
+ * "sysctl /net/homa/flags".
+ */
+
+/**
+ * Disable the output throttling mechanism: always send all packets
+ * immediately.
+ */
+#define HOMA_FLAG_DONT_THROTTLE   2
+
+int     homa_send(int sockfd, const void *message_buf,
+		  size_t length, const union sockaddr_in_union *dest_addr,
+		  uint64_t *id, uint64_t completion_cookie);
+int     homa_sendv(int sockfd, const struct iovec *iov,
+		   int iovcnt, const union sockaddr_in_union *dest_addr,
+		   uint64_t *id, uint64_t completion_cookie);
+ssize_t homa_reply(int sockfd, const void *message_buf,
+		   size_t length, const union sockaddr_in_union *dest_addr,
+		   uint64_t id);
+ssize_t homa_replyv(int sockfd, const struct iovec *iov,
+		    int iovcnt, const union sockaddr_in_union *dest_addr,
+		    uint64_t id);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _UAPI_LINUX_HOMA_H */
