17.4. Directives¶

This section details the directives of the Partition Manager. A subsection is dedicated to each of this manager’s directives and lists the calling sequence, parameters, description, return values, and notes of the directive.

17.4.1. rtems_partition_create()¶

Creates a partition.

CALLING SEQUENCE:

rtems_status_code rtems_partition_create(
  rtems_name      name,
  void           *starting_address,
  uintptr_t       length,
  size_t          buffer_size,
  rtems_attribute attribute_set,
  rtems_id       *id
);

PARAMETERS:

name: This parameter is the object name of the partition.
starting_address: This parameter is the starting address of the buffer area used by the partition.
length: This parameter is the length in bytes of the buffer area used by the partition.
buffer_size: This parameter is the size in bytes of a buffer managed by the partition.
attribute_set: This parameter is the attribute set of the partition.
id: This parameter is the pointer to an rtems_id object. When the directive call is successful, the identifier of the created partition will be stored in this object.

DESCRIPTION:

This directive creates a partition of fixed size buffers from a physically contiguous memory space which starts at starting_address and is length bytes in size. Each allocated buffer is to be of buffer_size in bytes. The partition has the user-defined object name specified in name. The assigned object identifier is returned in id. This identifier is used to access the partition with other partition related directives.

The attribute set specified in attribute_set is built through a bitwise or of the attribute constants described below. Not all combinations of attributes are allowed. Some attributes are mutually exclusive. If mutually exclusive attributes are combined, the behaviour is undefined. Attributes not mentioned below are not evaluated by this directive and have no effect. Default attributes can be selected by using the RTEMS_DEFAULT_ATTRIBUTES constant.

The partition has a local or global scope in a multiprocessing network (this attribute does not refer to SMP systems). The scope is selected by the mutually exclusive RTEMS_LOCAL and RTEMS_GLOBAL attributes.

A local scope is the default and can be emphasized through the use of the RTEMS_LOCAL attribute. A local partition can be only used by the node which created it.
A global scope is established if the RTEMS_GLOBAL attribute is set. The memory space used for the partition must reside in shared memory. Setting the global attribute in a single node system has no effect.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_NAME: The name parameter was invalid.
RTEMS_INVALID_ADDRESS: The id parameter was NULL.
RTEMS_INVALID_SIZE: The length parameter was 0.
RTEMS_INVALID_SIZE: The buffer_size parameter was 0.
RTEMS_INVALID_SIZE: The length parameter was less than the buffer_size parameter.
RTEMS_INVALID_SIZE: The buffer_size parameter was not an integral multiple of the pointer size.
RTEMS_INVALID_SIZE: The buffer_size parameter was less than two times the pointer size.
RTEMS_INVALID_ADDRESS: The starting_address parameter was not on a pointer size boundary.
RTEMS_TOO_MANY: There was no inactive object available to create a partition. The number of partitions available to the application is configured through the CONFIGURE_MAXIMUM_PARTITIONS application configuration option.
RTEMS_TOO_MANY: In multiprocessing configurations, there was no inactive global object available to create a global semaphore. The number of global objects available to the application is configured through the CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS application configuration option.

NOTES:

The partition buffer area specified by the starting_address must be properly aligned. It must be possible to directly store target architecture pointers and also the user data. For example, if the user data contains some long double or vector data types, the partition buffer area and the buffer size must take the alignment of these types into account which is usually larger than the pointer alignment. A cache line alignment may be also a factor. Use RTEMS_PARTITION_ALIGNMENT to specify the minimum alignment of a partition buffer type.

The buffer_size parameter must be an integral multiple of the pointer size on the target architecture. Additionally, buffer_size must be large enough to hold two pointers on the target architecture. This is required for RTEMS to manage the buffers when they are free.

For control and maintenance of the partition, RTEMS allocates a PTCB from the local PTCB free pool and initializes it. Memory from the partition buffer area is not used by RTEMS to store the PTCB.

The PTCB for a global partition is allocated on the local node. Partitions should not be made global unless remote tasks must interact with the partition. This is to avoid the overhead incurred by the creation of a global partition. When a global partition is created, the partition’s name and identifier must be transmitted to every node in the system for insertion in the local copy of the global object table.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive may obtain and release the object allocator mutex. This may cause the calling task to be preempted.
When the directive operates on a global object, the directive sends a message to remote nodes. This may preempt the calling task.
The number of partitions available to the application is configured through the CONFIGURE_MAXIMUM_PARTITIONS application configuration option.
Where the object class corresponding to the directive is configured to use unlimited objects, the directive may allocate memory from the RTEMS Workspace.
The number of global objects available to the application is configured through the CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS application configuration option.

17.4.2. rtems_partition_ident()¶

Identifies a partition by the object name.

CALLING SEQUENCE:

rtems_status_code rtems_partition_ident(
  rtems_name name,
  uint32_t   node,
  rtems_id  *id
);

PARAMETERS:

name: This parameter is the object name to look up.
node: This parameter is the node or node set to search for a matching object.
id: This parameter is the pointer to an rtems_id object. When the directive call is successful, the object identifier of an object with the specified name will be stored in this object.

DESCRIPTION:

This directive obtains a partition identifier associated with the partition name specified in name.

The node to search is specified in node. It shall be

a valid node number,
the constant RTEMS_SEARCH_ALL_NODES to search in all nodes,
the constant RTEMS_SEARCH_LOCAL_NODE to search in the local node only, or
the constant RTEMS_SEARCH_OTHER_NODES to search in all nodes except the local node.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ADDRESS: The id parameter was NULL.
RTEMS_INVALID_NAME: The name parameter was 0.
RTEMS_INVALID_NAME: There was no object with the specified name on the specified nodes.
RTEMS_INVALID_NODE: In multiprocessing configurations, the specified node was invalid.

NOTES:

If the partition name is not unique, then the partition identifier will match the first partition with that name in the search order. However, this partition identifier is not guaranteed to correspond to the desired partition.

The objects are searched from lowest to the highest index. If node is RTEMS_SEARCH_ALL_NODES, all nodes are searched with the local node being searched first. All other nodes are searched from lowest to the highest node number.

If node is a valid node number which does not represent the local node, then only the partitions exported by the designated node are searched.

This directive does not generate activity on remote nodes. It accesses only the local copy of the global object table.

The partition identifier is used with other partition related directives to access the partition.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within any runtime context.
The directive will not cause the calling task to be preempted.

17.4.3. rtems_partition_delete()¶

Deletes the partition.

CALLING SEQUENCE:

rtems_status_code rtems_partition_delete( rtems_id id );

PARAMETERS:

id: This parameter is the partition identifier.

DESCRIPTION:

This directive deletes the partition specified by id.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ID: There was no partition associated with the identifier specified by id.
RTEMS_ILLEGAL_ON_REMOTE_OBJECT: The partition resided on a remote node.
RTEMS_RESOURCE_IN_USE: There were buffers of the partition still in use.

NOTES:

The partition cannot be deleted if any of its buffers are still allocated.

The PTCB for the deleted partition is reclaimed by RTEMS.

When a global partition is deleted, the partition identifier must be transmitted to every node in the system for deletion from the local copy of the global object table.

The partition must reside on the local node, even if the partition was created with the RTEMS_GLOBAL attribute.

CONSTRAINTS:

The following constraints apply to this directive:

The directive may be called from within device driver initialization context.
The directive may be called from within task context.
The directive may obtain and release the object allocator mutex. This may cause the calling task to be preempted.
When the directive operates on a global object, the directive sends a message to remote nodes. This may preempt the calling task.
The calling task does not have to be the task that created the object. Any local task that knows the object identifier can delete the object.
Where the object class corresponding to the directive is configured to use unlimited objects, the directive may free memory to the RTEMS Workspace.

17.4.4. rtems_partition_get_buffer()¶

Tries to get a buffer from the partition.

CALLING SEQUENCE:

rtems_status_code rtems_partition_get_buffer( rtems_id id, void **buffer );

PARAMETERS:

id: This parameter is the partition identifier.
buffer: This parameter is the pointer to a void pointer object. When the directive call is successful, the pointer to the allocated buffer will be stored in this object.

DESCRIPTION:

This directive allows a buffer to be obtained from the partition specified by id. The address of the allocated buffer is returned through the buffer parameter.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ID: There was no partition associated with the identifier specified by id.
RTEMS_INVALID_ADDRESS: The buffer parameter was NULL.
RTEMS_UNSATISFIED: There was no free buffer available to allocate and return.

NOTES:

The buffer start alignment is determined by the memory area and buffer size used to create the partition.

A task cannot wait on a buffer to become available.

Getting a buffer from a global partition which does not reside on the local node will generate a request telling the remote node to allocate a buffer from the partition.

CONSTRAINTS:

The following constraints apply to this directive:

When the directive operates on a local object, the directive may be called from within interrupt context.
The directive may be called from within task context.
When the directive operates on a local object, the directive will not cause the calling task to be preempted.
When the directive operates on a remote object, the directive sends a message to the remote node and waits for a reply. This will preempt the calling task.

17.4.5. rtems_partition_return_buffer()¶

Returns the buffer to the partition.

CALLING SEQUENCE:

rtems_status_code rtems_partition_return_buffer( rtems_id id, void *buffer );

PARAMETERS:

id: This parameter is the partition identifier.
buffer: This parameter is the pointer to the buffer to return.

DESCRIPTION:

This directive returns the buffer specified by buffer to the partition specified by id.

RETURN VALUES:

RTEMS_SUCCESSFUL: The requested operation was successful.
RTEMS_INVALID_ID: There was no partition associated with the identifier specified by id.
RTEMS_INVALID_ADDRESS: The buffer referenced by buffer was not in the partition.

NOTES:

Returning a buffer multiple times is an error. It will corrupt the internal state of the partition.

CONSTRAINTS:

The following constraints apply to this directive:

When the directive operates on a local object, the directive may be called from within interrupt context.
The directive may be called from within task context.
When the directive operates on a local object, the directive will not cause the calling task to be preempted.
When the directive operates on a remote object, the directive sends a message to the remote node and waits for a reply. This will preempt the calling task.