Trusty provides APIs for developing two classes of apps and services:
- Trusted apps and services that run on the TEE processor
- Normal and untrusted apps that run on the main processor and use the services provided by trusted apps
The Trusty API generally describes the Trusty inter-process communication (IPC) system, including communications with the non-secure world. Software running on the main processor can use Trusty APIs to connect to trusted apps and services and exchange arbitrary messages with them just like a network service over IP. It is up to the app to determine the data format and semantics of these messages using an app-level protocol. Reliable delivery of messages is guaranteed by the underlying Trusty infrastructure (in the form of drivers running on the main processor), and the communication is completely asynchronous.
Ports and channels
Ports are used by Trusty apps to expose service end-points in the form
of a named path to which clients connect. This gives a simple, string-based
service ID for clients to use. The naming convention is reverse-DNS-style
naming, e.g. com.google.servicename.
When a client connects to a port, the client receives a channel for interacting with a service. The service must accept an incoming connection, and when it does, it too receives a channel. In essence, ports are used to look up services and then communication occurs over a pair of connected channels (i.e., connection instances on a port). When a client connects to a port, a symmetric, bi-directional connection is established. Using this full-duplex path, clients and servers can exchange arbitrary messages until either side decides to tear down the connection.
Only secure-side trusted apps or Trusty kernel modules can create ports. Apps running on the non-secure side (in the normal world) can only connect to services published by the secure side.
Depending on requirements, a trusted app can be both a client and a server at the same time. A trusted app that publishes a service (as a server) might need to connect to other services (as a client).
Handle API
Handles are unsigned integers representing resources such as ports and channels, similar to file descriptors in UNIX. After handles are created, they are placed into an app-specific handle table and can be referenced later.
A caller can associate private data with a handle by using
the set_cookie() method.
Methods in the Handle API
Handles are only valid in the context of an app. An app should
not pass the value of a handle to other apps unless explicitly
specified. A handle value only should be interpreted by comparing it with
the INVALID_IPC_HANDLE #define, which an app can use as an
indication that a handle is invalid or unset.
set_cookie()
Associates the caller-provided private data with a specified handle.
long set_cookie(uint32_t handle, void *cookie)
[in] handle: Any handle returned by one of the API calls
[in] cookie: Pointer to arbitrary user-space data in the Trusty app
[retval]: NO_ERROR on success, < 0 error code otherwise
This call is useful for handling events when they occur at a later time after the handle has been created. The event-handling mechanism supplies the handle and its cookie back to the event handler.
Handles can be waited upon for events by using the wait() call.
wait()
Waits for an event to occur on a given handle for specified period of time.
long wait(uint32_t handle_id, uevent_t *event, unsigned long timeout_msecs)
[in] handle_id: Any handle returned by one of the API calls
[out] event: A pointer to the structure representing
an event that occurred on this handle
[in] timeout_msecs: A timeout value in milliseconds; a
value of -1 is an infinite timeout
[retval]: NO_ERROR if a valid event occurred within a
specified timeout interval; ERR_TIMED_OUT if a specified timeout elapsed but no
event has occurred; < 0 for other errors
Upon success (retval == NO_ERROR), the wait() call
fills a specified uevent_t structure with information about
the event that occurred.
typedef struct uevent {
uint32_t handle; /* handle this event is related to */
uint32_t event; /* combination of IPC_HANDLE_POLL_XXX flags */
void *cookie; /* cookie associated with this handle */
} uevent_t;
The event field contains a combination of the following values:
enum {
IPC_HANDLE_POLL_NONE = 0x0,
IPC_HANDLE_POLL_READY = 0x1,
IPC_HANDLE_POLL_ERROR = 0x2,
IPC_HANDLE_POLL_HUP = 0x4,
IPC_HANDLE_POLL_MSG = 0x8,
IPC_HANDLE_POLL_SEND_UNBLOCKED = 0x10,
… more values[TBD]
};
IPC_HANDLE_POLL_NONE - no events are actually pending,
caller should restart the wait
IPC_HANDLE_POLL_ERROR - an unspecified internal error has occurred
IPC_HANDLE_POLL_READY - depends on the handle type, as follows:
- For ports, this value indicates that there is a pending connection
- For channels, this value indicates that an asynchronous connection
(see
connect()) was established
The following events are only relevant for channels:
IPC_HANDLE_POLL_HUP- indicates that a channel has been closed by a peerIPC_HANDLE_POLL_MSG- indicates that there is a pending message for this channelIPC_HANDLE_POLL_SEND_UNBLOCKED- indicates that a previously send-blocked caller may attempt to send a message again (see the description ofsend_msg()for details)
An event handler should be prepared to handle a combination of specified events, as multiple bits might be set at the same time. For example, for a channel, it is possible to have pending messages, and a connection closed by a peer at the same time.
Most events are sticky. They persist as long as the underlying condition
persists (for example all pending messages are received and pending connection
requests are handled). The exception is the case of
the IPC_HANDLE_POLL_SEND_UNBLOCKED event, which
is cleared upon a read and the app has only one chance to
handle it.
Handles can be destroyed by calling the close() method.
close()
Destroys the resource associated with the specified handle and removes it from the handle table.
long close(uint32_t handle_id);
[in] handle_id: Handle to destroy
[retval]: 0 if success; a negative error otherwise
Server API
A server begins by creating one or more named ports representing its service end-points. Each port is represented by a handle.
Methods in the Server API
port_create()
Creates a named service port.
long port_create (const char *path, uint num_recv_bufs, size_t recv_buf_size, uint32_t flags)
[in] path: The string name of the port (as described above). This
name should be unique across the system; attempts to create a duplicate fail.
[in] num_recv_bufs: The maximum number of buffers that a channel on
this port can pre-allocate to facilitate the exchange of data with the client. Buffers are counted
separately for data going in both directions, so specifying 1 here would mean 1
send and 1 receive buffer are preallocated. In general, the number of buffers
required depends on the higher-level protocol agreement between the client and
server. The number can be as little as 1 in case of a very synchronous protocol
(send message, receive reply before sending another). But the number can be
more if the client expects to send more than one message before a reply can
appear (e.g, one message as a prologue and another as the actual command). The
allocated buffer sets are per channel, so two separate connections (channels)
would have separate buffer sets.
[in] recv_buf_size: Maximum size of each individual buffer in the
above buffer set. This value is
protocol-dependent and effectively limits maximum message size you can exchange
with peer
[in] flags: A combination of flags that specifies additional port behavior
This value should be a combination of the following values:
IPC_PORT_ALLOW_TA_CONNECT - allows a connection from other secure apps
IPC_PORT_ALLOW_NS_CONNECT - allows a connection from the non-secure world
[retval]: Handle to the port created if non-negative or a specific error if negative
The server then polls the list of port handles for incoming connections
using wait() call. Upon receiving a connection
request indicated by the IPC_HANDLE_POLL_READY bit set in
the event field of the uevent_t structure, the
server should call accept() to finish establishing a connection and create a
channel (represented by
another handle) that can then be polled for incoming messages.
accept()
Accepts an incoming connection and gets a handle to a channel.
long accept(uint32_t handle_id, uuid_t *peer_uuid);
[in] handle_id: Handle representing the port to which a client has connected
[out] peer_uuid: Pointer to a uuid_t structure to be
filled with the UUID of the connecting client app. It
is set to all zeros if the connection originated from the nonsecure world
[retval]: Handle to a channel (if non-negative) on which the server can exchange messages with the client (or an error code otherwise)
Client API
This section contains the methods in the Client API.
Methods in the Client API
connect()
Initiates a connection to a port specified by name.
long connect(const char *path, uint flags);
[in] path: Name of a port published by a Trusty app
[in] flags: Specifies additional, optional behavior
[retval]: Handle to a channel over which messages can be exchanged with the server; error if negative
If no flags are specified (the flags parameter
is set to 0), calling connect() initiates a synchronous connection
to a specified port that immediately
returns an error if the port doesn't exist, and creates a block until the
server otherwise accepts a connection.
This behavior can be altered by specifying a combination of two values, described below:
enum {
IPC_CONNECT_WAIT_FOR_PORT = 0x1,
IPC_CONNECT_ASYNC = 0x2,
};
IPC_CONNECT_WAIT_FOR_PORT - forces a connect()
call to wait if the specified port doesn't immediately exist at execution,
instead of failing immediately.
IPC_CONNECT_ASYNC - if set, initiates an asynchronous connection. An
app has to poll for
the returned handle by calling wait() for
a connection completion event indicated by the IPC_HANDLE_POLL_READY
bit set in the event field of the uevent_t structure before starting
normal operation.
Messaging API
The Messaging API calls enable the sending and reading of messages over a previously established connection (channel). The Messaging API calls are the same for servers and clients.
A client receives a handle to a channel by issuing a connect()
call, and a server gets a channel handle from an accept() call,
described above.
Structure of a Trusty message
As shown in the following, messages exchanged by the Trusty API have a minimal structure, leaving it to the server and client to agree on the semantics of the actual contents:
/*
* IPC message
*/
typedef struct iovec {
void *base;
size_t len;
} iovec_t;
typedef struct ipc_msg {
uint num_iov; /* number of iovs in this message */
iovec_t *iov; /* pointer to iov array */
uint num_handles; /* reserved, currently not supported */
handle_t *handles; /* reserved, currently not supported */
} ipc_msg_t;
A message can be composed of one or more non-contiguous buffers represented by
an array of iovec_t structures. Trusty performs scatter-gather
reads and writes to these blocks
using the iov array. The content of buffers that can be described
by the iov array is completely arbitrary.
Methods in the Messaging API
send_msg()
Sends a message over a specified channel.
long send_msg(uint32_t handle, ipc_msg_t *msg);
[in] handle: Handle to the channel over which to send the message
[in] msg: Pointer to the ipc_msg_t structure describing the message
[retval]: Total number of bytes sent on success; a negative error otherwise
If the client (or server) is trying to send a message over the channel and
there is no space in the destination peer message queue, the channel might
enter a send-blocked state (this should never happen for a simple synchronous
request/reply protocol but might happen in more complicated cases) that is
indicated by returning an ERR_NOT_ENOUGH_BUFFER error code.
In such a case the caller must wait until the peer frees some
space in its receive queue by retrieving the handling and retiring messages,
indicated by the IPC_HANDLE_POLL_SEND_UNBLOCKED bit set in
the event field of the uevent_t structure
returned by the wait() call.
get_msg()
Gets meta-information about the next message in an incoming message queue
of a specified channel.
long get_msg(uint32_t handle, ipc_msg_info_t *msg_info);
[in] handle: Handle of the channel on which a new message must be retrieved
[out] msg_info: Message information structure described as follows:
typedef struct ipc_msg_info {
size_t len; /* total message length */
uint32_t id; /* message id */
} ipc_msg_info_t;
Each message is assigned a unique ID across the set of outstanding messages, and the total length of each message is filled in. If configured and allowed by the protocol, there can be multiple outstanding (opened) messages at once for a particular channel.
[retval]: NO_ERROR on success; a negative error otherwise
read_msg()
Reads the content of the message with the specified ID starting from the specified offset.
long read_msg(uint32_t handle, uint32_t msg_id, uint32_t offset, ipc_msg_t *msg);
[in] handle: Handle of the channel from which to read the message
[in] msg_id: ID of the message to read
[in] offset: Offset into the message from which to start reading
[out] msg: Pointer to the ipc_msg_t structure describing
a set of buffers into which to store incoming message
data
[retval]: Total number of bytes stored in the msg buffers on
success; a negative error otherwise
The read_msg method can be called multiple times starting at
a different (not necessarily
sequential) offset as needed.
put_msg()
Retires a message with a specified ID.
long put_msg(uint32_t handle, uint32_t msg_id);
[in] handle: Handle of the channel on which the message has arrived
[in] msg_id: ID of message being retired
[retval]: NO_ERROR on success; a negative error otherwise
Message content can't be accessed after a message has been retired and the buffer it occupied has been freed.
File Descriptor API
The File Descriptor API includes read(), write(),
and ioctl() calls. All of these calls can operate on a predefined (static) set of file
descriptors traditionally represented by small numbers. In the current
implementation, the file descriptor space is separate from the IPC handle
space. The File Descriptor API in Trusty is
similar to a traditional file descriptor-based API.
By default, there are 3 predefined (standard and well-known) file descriptors:
- 0 - standard input. The default implementation of standard input
fdis a no-op (as trusted apps aren't expected to have an interactive console) so reading, writing or invokingioctl()onfd0 should return anERR_NOT_SUPPORTEDerror. - 1 - standard output. Data written to standard output can be routed (depending
on the LK debug level) to UART and/or a memory log available on the non-secure
side, depending on the platform and configuration. Non-critical debug logs and
messages should go in standard output. The
read()andioctl()methods are no-ops and should return anERR_NOT_SUPPORTEDerror. - 2 - standard error. Data written to standard error should be routed to the UART
or memory log available on the non-secure side, depending on the platform and
configuration. It is recommended to write only critical messages to standard
error, as this stream is very likely to be unthrottled. The
read()andioctl()methods are no-ops and should return anERR_NOT_SUPPORTEDerror.
Even though this set of file descriptors can be extended to implement more
fds (to implement platform-specific extensions), extending file descriptors needs
to be exercised with caution. Extending file descriptors is prone to create
conflicts and isn't generally recommended.
Methods in the File Descriptor API
read()
Attempts to read up to count bytes of data from a specified file descriptor.
long read(uint32_t fd, void *buf, uint32_t count);
[in] fd: File descriptor from which to read
[out] buf: Pointer to a buffer into which to store data
[in] count: Maximum number of bytes to read
[retval]: Returned number of bytes read; a negative error otherwise
write()
Writes up to count bytes of data to specified file descriptor.
long write(uint32_t fd, void *buf, uint32_t count);
[in] fd: File descriptor to which to write
[out] buf: Pointer to data to write
[in] count: Maximum number of bytes to write
[retval]: Returned number of bytes written; a negative error otherwise
ioctl()
Invokes a specified ioctl command for a given file descriptor.
long ioctl(uint32_t fd, uint32_t cmd, void *args);
[in] fd: File descriptor on which to invoke ioctl()
[in] cmd: The ioctl command
[in/out] args: Pointer to ioctl() arguments
Miscellaneous API
Methods in the Miscellaneous API
gettime()
Returns the current system time (in nanoseconds).
long gettime(uint32_t clock_id, uint32_t flags, int64_t *time);
[in] clock_id: Platform-dependent; pass zero for default
[in] flags: Reserved, should be zero
[out] time: Pointer to an int64_t value to which to store the current time
[retval]: NO_ERROR on success; a negative error otherwise
nanosleep()
Suspends execution of the calling app for a specified period of time and resumes it after that period.
long nanosleep(uint32_t clock_id, uint32_t flags, uint64_t sleep_time)
[in] clock_id: Reserved, should be zero
[in] flags: Reserved, should be zero
[in] sleep_time: Sleep time in nanoseconds
[retval]: NO_ERROR on success; a negative error otherwise
Example of a trusted app server
The following sample app shows the usage of the above APIs. The sample creates an "echo" service that handles multiple incoming connections and reflects back to the caller all messages it receives from clients originated from the secure or non-secure side.
#include <uapi/err.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <trusty_ipc.h>
#define LOG_TAG "echo_srv"
#define TLOGE(fmt, ...) \
fprintf(stderr, "%s: %d: " fmt, LOG_TAG, __LINE__, ##__VA_ARGS__)
# define MAX_ECHO_MSG_SIZE 64
static
const char * srv_name = "com.android.echo.srv.echo";
static uint8_t msg_buf[MAX_ECHO_MSG_SIZE];
/*
* Message handler
*/
static int handle_msg(handle_t chan) {
int rc;
struct iovec iov;
ipc_msg_t msg;
ipc_msg_info_t msg_inf;
iov.iov_base = msg_buf;
iov.iov_len = sizeof(msg_buf);
msg.num_iov = 1;
msg.iov = &iov;
msg.num_handles = 0;
msg.handles = NULL;
/* get message info */
rc = get_msg(chan, &msg_inf);
if (rc == ERR_NO_MSG)
return NO_ERROR; /* no new messages */
if (rc != NO_ERROR) {
TLOGE("failed (%d) to get_msg for chan (%d)\n",
rc, chan);
return rc;
}
/* read msg content */
rc = read_msg(chan, msg_inf.id, 0, &msg);
if (rc < 0) {
TLOGE("failed (%d) to read_msg for chan (%d)\n",
rc, chan);
return rc;
}
/* update number of bytes received */
iov.iov_len = (size_t) rc;
/* send message back to the caller */
rc = send_msg(chan, &msg);
if (rc < 0) {
TLOGE("failed (%d) to send_msg for chan (%d)\n",
rc, chan);
return rc;
}
/* retire message */
rc = put_msg(chan, msg_inf.id);
if (rc != NO_ERROR) {
TLOGE("failed (%d) to put_msg for chan (%d)\n",
rc, chan);
return rc;
}
return NO_ERROR;
}
/*
* Channel event handler
*/
static void handle_channel_event(const uevent_t * ev) {
int rc;
if (ev->event & IPC_HANDLE_POLL_MSG) {
rc = handle_msg(ev->handle);
if (rc != NO_ERROR) {
/* report an error and close channel */
TLOGE("failed (%d) to handle event on channel %d\n",
rc, ev->handle);
close(ev->handle);
}
return;
}
if (ev->event & IPC_HANDLE_POLL_HUP) {
/* closed by peer. */
close(ev->handle);
return;
}
}
/*
* Port event handler
*/
static void handle_port_event(const uevent_t * ev) {
uuid_t peer_uuid;
if ((ev->event & IPC_HANDLE_POLL_ERROR) ||
(ev->event & IPC_HANDLE_POLL_HUP) ||
(ev->event & IPC_HANDLE_POLL_MSG) ||
(ev->event & IPC_HANDLE_POLL_SEND_UNBLOCKED)) {
/* should never happen with port handles */
TLOGE("error event (0x%x) for port (%d)\n",
ev->event, ev->handle);
abort();
}
if (ev->event & IPC_HANDLE_POLL_READY) {
/* incoming connection: accept it */
int rc = accept(ev->handle, &peer_uuid);
if (rc < 0) {
TLOGE("failed (%d) to accept on port %d\n",
rc, ev->handle);
return;
}
handle_t chan = rc;
while (true){
struct uevent cev;
rc = wait(chan, &cev, INFINITE_TIME);
if (rc < 0) {
TLOGE("wait returned (%d)\n", rc);
abort();
}
handle_channel_event(&cev);
if (cev.event & IPC_HANDLE_POLL_HUP) {
return;
}
}
}
}
/*
* Main app entry point
*/
int main(void) {
int rc;
handle_t port;
/* Initialize service */
rc = port_create(srv_name, 1, MAX_ECHO_MSG_SIZE,
IPC_PORT_ALLOW_NS_CONNECT |
IPC_PORT_ALLOW_TA_CONNECT);
if (rc < 0) {
TLOGE("Failed (%d) to create port %s\n",
rc, srv_name);
abort();
}
port = (handle_t) rc;
/* enter main event loop */
while (true) {
uevent_t ev;
ev.handle = INVALID_IPC_HANDLE;
ev.event = 0;
ev.cookie = NULL;
/* wait forever */
rc = wait(port, &ev, INFINITE_TIME);
if (rc == NO_ERROR) {
/* got an event */
handle_port_event(&ev);
} else {
TLOGE("wait returned (%d)\n", rc);
abort();
}
}
return 0;
}
The run_end_to_end_msg_test() method sends 10,000 messages asynchronously
to the "echo" service and handles
replies.
static int run_echo_test(void)
{
int rc;
handle_t chan;
uevent_t uevt;
uint8_t tx_buf[64];
uint8_t rx_buf[64];
ipc_msg_info_t inf;
ipc_msg_t tx_msg;
iovec_t tx_iov;
ipc_msg_t rx_msg;
iovec_t rx_iov;
/* prepare tx message buffer */
tx_iov.base = tx_buf;
tx_iov.len = sizeof(tx_buf);
tx_msg.num_iov = 1;
tx_msg.iov = &tx_iov;
tx_msg.num_handles = 0;
tx_msg.handles = NULL;
memset (tx_buf, 0x55, sizeof(tx_buf));
/* prepare rx message buffer */
rx_iov.base = rx_buf;
rx_iov.len = sizeof(rx_buf);
rx_msg.num_iov = 1;
rx_msg.iov = &rx_iov;
rx_msg.num_handles = 0;
rx_msg.handles = NULL;
/* open connection to echo service */
rc = sync_connect(srv_name, 1000);
if(rc < 0)
return rc;
/* got channel */
chan = (handle_t)rc;
/* send/receive 10000 messages asynchronously. */
uint tx_cnt = 10000;
uint rx_cnt = 10000;
while (tx_cnt || rx_cnt) {
/* send messages until all buffers are full */
while (tx_cnt) {
rc = send_msg(chan, &tx_msg);
if (rc == ERR_NOT_ENOUGH_BUFFER)
break; /* no more space */
if (rc != 64) {
if (rc > 0) {
/* incomplete send */
rc = ERR_NOT_VALID;
}
goto abort_test;
}
tx_cnt--;
}
/* wait for reply msg or room */
rc = wait(chan, &uevt, 1000);
if (rc != NO_ERROR)
goto abort_test;
/* drain all messages */
while (rx_cnt) {
/* get a reply */
rc = get_msg(chan, &inf);
if (rc == ERR_NO_MSG)
break; /* no more messages */
if (rc != NO_ERROR)
goto abort_test;
/* read reply data */
rc = read_msg(chan, inf.id, 0, &rx_msg);
if (rc != 64) {
/* unexpected reply length */
rc = ERR_NOT_VALID;
goto abort_test;
}
/* discard reply */
rc = put_msg(chan, inf.id);
if (rc != NO_ERROR)
goto abort_test;
rx_cnt--;
}
}
abort_test:
close(chan);
return rc;
}
Non-secure world APIs and apps
A set of Trusty services, published from the secure side and marked with
the IPC_PORT_ALLOW_NS_CONNECT attribute, are accessible to kernel
and user space programs running on the
non-secure side.
The execution environment on the non-secure side (kernel and user space) is drastically different from the execution environment on the secure-side. Therefore, rather than a single library for both environments, there are two different sets of APIs. In the kernel, the Client API is provided by the trusty-ipc kernel driver and registers a character device node that can be used by user space processes to communicate with services running on the secure side.
User space Trusty IPC Client API
The user space Trusty IPC Client API library is a thin layer on top of the
device node fd.
A user space program starts a communication session
by calling tipc_connect(),
initializing a connection to a specified Trusty service. Internally,
the tipc_connect() call opens a specified device node to
obtain a file descriptor and invokes a TIPC_IOC_CONNECT ioctl()
call with the argp parameter pointing to a string containing a
service name to which to connect.
#define TIPC_IOC_MAGIC 'r' #define TIPC_IOC_CONNECT _IOW(TIPC_IOC_MAGIC, 0x80, char *)
The resulting file descriptor can only be used to communicate with the service
for which it was created. The file descriptor should be closed by
calling tipc_close() when the connection isn't required anymore.
The file descriptor obtained by the tipc_connect() call
behaves as a typical character device node; the file descriptor:
- Can be switched to non-blocking mode if needed
- Can be written to using a standard
write()call to send messages to the other side - Can be polled (using
poll()calls orselect()calls) for availability of incoming messages as a regular file descriptor - Can be read to retrieve incoming messages
A caller sends a message to the Trusty service by executing a write call for
the specified fd. All data passed to the above write() call
is transformed into a message by the trusty-ipc driver. The message is
delivered to the secure side where the data is handled by the IPC subsystem in
the Trusty kernel and routed to the proper destination and delivered to an app
event loop as an IPC_HANDLE_POLL_MSG event on a particular channel
handle. Depending on the particular,
service-specific protocol, the Trusty service may send one or more reply
messages that are delivered back to the non-secure side and placed in the
appropriate channel file descriptor message queue to be retrieved by the user
space app read() call.
tipc_connect()
Opens a specified tipc device node and initiates a
connection to a specified Trusty service.
int tipc_connect(const char *dev_name, const char *srv_name);
[in] dev_name: Path to the Trusty IPC device node to open
[in] srv_name: Name of a published Trusty service to which to connect
[retval]: Valid file descriptor on success, -1 otherwise.
tipc_close()
Closes the connection to the Trusty service specified by a file descriptor.
int tipc_close(int fd);
[in] fd: File descriptor previously opened by
a tipc_connect() call
Kernel Trusty IPC Client API
The kernel Trusty IPC Client API is available for kernel drivers. The user space Trusty IPC API is implemented on top of this API.
In general, typical usage of this API consists of a caller creating
a struct tipc_chan object by using the tipc_create_channel()
function and then using the tipc_chan_connect() call to initiate a
connection to the Trusty IPC service running on the secure
side. The connection to the remote side can be terminated by
calling tipc_chan_shutdown() followed by
tipc_chan_destroy() to clean up resources.
Upon receiving a notification (through the handle_event() callback)
that a connection has been successfully established, a caller does
the following:
- Obtains a message buffer using the
tipc_chan_get_txbuf_timeout()call - Composes a message, and
- Queues the message using the
tipc_chan_queue_msg()method for delivery to a Trusty service (on the secure side), to which the channel is connected
After queueing is successful, the caller should forget the message buffer
because the message buffer eventually returns to the free buffer pool after
processing by the remote side (for reuse later, for other messages). The user
only needs to call tipc_chan_put_txbuf() if it fails to
queue such buffer or it isn't required anymore.
An API user receives messages from the remote side by handling a
handle_msg() notification callback (which is called in
the context of the trusty-ipc rx workqueue) that
provides a pointer to an rx buffer containing an
incoming message to be handled.
It is expected that the handle_msg() callback
implementation returns a pointer to a valid struct tipc_msg_buf.
It can be the same as the incoming message buffer if it is handled locally
and not required anymore. Alternatively, it can be a new buffer obtained by
a tipc_chan_get_rxbuf() call if the incoming buffer is queued
for further processing. A detached rx buffer must be tracked
and eventually released using a tipc_chan_put_rxbuf() call when
it is no longer needed.
Methods in the Kernel Trusty IPC Client API
tipc_create_channel()
Creates and configures an instance of a Trusty IPC channel for a particular trusty-ipc device.
struct tipc_chan *tipc_create_channel(struct device *dev,
const struct tipc_chan_ops *ops,
void *cb_arg);
[in] dev: Pointer to the trusty-ipc for which the device
channel is created
[in] ops: Pointer to a struct tipc_chan_ops,
with caller-specific
callbacks filled in
[in] cb_arg: Pointer to data that is passed
to tipc_chan_ops callbacks
[retval]: Pointer to a newly-created instance of
struct tipc_chan on success,
ERR_PTR(err) otherwise
In general, a caller must provide two callbacks that are asynchronously invoked when the corresponding activity is occurring.
The void (*handle_event)(void *cb_arg, int event)event is invoked
to notify a caller about a channel state change.
[in] cb_arg: Pointer to data passed to a
tipc_create_channel() call
[in] event: An event that can be one of the following values:
TIPC_CHANNEL_CONNECTED- indicates a successful connection to the remote sideTIPC_CHANNEL_DISCONNECTED- indicates the remote side denied the new connection request or requested disconnection for the previously connected channelTIPC_CHANNEL_SHUTDOWN- indicates the remote side is shutting down, permanently terminating all connections
The struct tipc_msg_buf *(*handle_msg)(void *cb_arg, struct tipc_msg_buf *mb)
callback is invoked to provide notification that a new message has been
received over a specified channel:
- [in]
cb_arg: Pointer to data passed to thetipc_create_channel()call - [in]
mb: Pointer to astruct tipc_msg_bufdescribing an incoming message - [retval]: The callback implementation is expected to return a pointer to a
struct tipc_msg_bufthat can be the same pointer received as anmbparameter if the message is handled locally and isn't required anymore (or it can be a new buffer obtained by thetipc_chan_get_rxbuf()call)
tipc_chan_connect()
Initiates a connection to the specified Trusty IPC service.
int tipc_chan_connect(struct tipc_chan *chan, const char *port);
[in] chan: Pointer to a channel returned by the
tipc_create_chan() call
[in] port: Pointer to a string containing the
service name to which to connect
[retval]: 0 on success, a negative error otherwise
The caller is notified when a connection is established by receiving a
handle_event callback.
tipc_chan_shutdown()
Terminates a connection to the Trusty IPC service previously initiated
by a tipc_chan_connect() call.
int tipc_chan_shutdown(struct tipc_chan *chan);
[in] chan: Pointer to a channel returned by
a tipc_create_chan() call
tipc_chan_destroy()
Destroys a specified Trusty IPC channel.
void tipc_chan_destroy(struct tipc_chan *chan);
[in] chan: Pointer to a channel returned by the
tipc_create_chan() call
tipc_chan_get_txbuf_timeout()
Obtains a message buffer that can be used to send data over a specified channel. If the buffer isn't immediately available the caller may be blocked for the specified timeout (in milliseconds).
struct tipc_msg_buf * tipc_chan_get_txbuf_timeout(struct tipc_chan *chan, long timeout);
[in] chan: Pointer to the channel to which to queue a message
[in] chan: Maximum timeout to wait until the
tx buffer becomes available
[retval]: A valid message buffer on success,
ERR_PTR(err) on error
tipc_chan_queue_msg()
Queues a message to be sent over the specified Trusty IPC channels.
int tipc_chan_queue_msg(struct tipc_chan *chan, struct tipc_msg_buf *mb);
[in] chan: Pointer to the channel to which to queue the message
[in] mb: Pointer to the message to queue
(obtained by a tipc_chan_get_txbuf_timeout() call)
[retval]: 0 on success, a negative error otherwise
tipc_chan_put_txbuf()
Releases the specified Tx message buffer
previously obtained by a tipc_chan_get_txbuf_timeout() call.
void tipc_chan_put_txbuf(struct tipc_chan *chan,
struct tipc_msg_buf *mb);
[in] chan: Pointer to the channel to which
this message buffer belongs
[in] mb: Pointer to the message buffer to release
[retval]: None
tipc_chan_get_rxbuf()
Obtains a new message buffer that can be used to receive messages over the specified channel.
struct tipc_msg_buf *tipc_chan_get_rxbuf(struct tipc_chan *chan);
[in] chan: Pointer to a channel to which this message buffer belongs
[retval]: A valid message buffer on success, ERR_PTR(err) on error
tipc_chan_put_rxbuf()
Releases a specified message buffer previously obtained by a
tipc_chan_get_rxbuf() call.
void tipc_chan_put_rxbuf(struct tipc_chan *chan,
struct tipc_msg_buf *mb);
[in] chan: Pointer to a channel to which this message buffer belongs
[in] mb: Pointer to a message buffer to release
[retval]: None