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A Mach message consists of a fixed size message header, a
mach_msg_header_t, followed by zero or more data items. Data
items are typed. Each item has a type descriptor followed by the actual
data (or the address of the data, for out-of-line memory regions).
The following data types are related to Mach ports:
mach_port_t data type is an unsigned integer type which
represents a port name in the task's port name space. In GNU Mach, this
is an unsigned int.
The following data types are related to Mach messages:
mach_msg_bits_t data type is an unsigned int used to
store various flags for a message.
mach_msg_size_t data type is an unsigned int used to
store the size of a message.
mach_msg_id_t data type is an integer_t typically used to
convey a function or operation id for the receiver.
mach_msg_bits_t msgh_bits
msgh_bits field has the following bits defined, all other
bits should be zero:
MACH_MSGH_BITS_REMOTE_MASK
MACH_MSGH_BITS_LOCAL_MASK
mach_msg_type_name_t values that
specify the port rights in the msgh_remote_port and
msgh_local_port fields. The remote value must specify a send or
send-once right for the destination of the message. If the local value
doesn't specify a send or send-once right for the message's reply port,
it must be zero and msgh_local_port must be MACH_PORT_NULL.
MACH_MSGH_BITS_COMPLEX
MACH_MSGH_BITS_REMOTE and MACH_MSGH_BITS_LOCAL macros
return the appropriate mach_msg_type_name_t values, given a
msgh_bits value. The MACH_MSGH_BITS macro constructs a
value for msgh_bits, given two mach_msg_type_name_t
values.
mach_msg_size_t msgh_size
msgh_size field in the header of a received message contains
the message's size. The message size, a byte quantity, includes the
message header, type descriptors, and in-line data. For out-of-line
memory regions, the message size includes the size of the in-line
address, not the size of the actual memory region. There are no
arbitrary limits on the size of a Mach message, the number of data items
in a message, or the size of the data items.
mach_port_t msgh_remote_port
msgh_remote_port field specifies the destination port of the
message. The field must carry a legitimate send or send-once right for
a port.
mach_port_t msgh_local_port
msgh_local_port field specifies an auxiliary port right,
which is conventionally used as a reply port by the recipient of the
message. The field must carry a send right, a send-once right,
MACH_PORT_NULL, or MACH_PORT_DEAD.
mach_port_seqno_t msgh_seqno
msgh_seqno field provides a sequence number for the message.
It is only valid in received messages; its value in sent messages is
overwritten.
mach_msg_id_t msgh_id
mach_msg call doesn't use the msgh_id field, but it
conventionally conveys an operation or function id.
mach_msg_type_name_t values that specify
the port rights in the msgh_remote_port and
msgh_local_port fields of a mach_msg call into an
appropriate mach_msg_bits_t value.
mach_msg_type_name_t value for the remote
port right in a mach_msg_bits_t value.
mach_msg_type_name_t value for the local
port right in a mach_msg_bits_t value.
mach_msg_bits_t component consisting of
the mach_msg_type_name_t values for the remote and local port
right in a mach_msg_bits_t value.
mach_msg_bits_t component consisting of
everything except the mach_msg_type_name_t values for the remote
and local port right in a mach_msg_bits_t value.
Each data item has a type descriptor, a mach_msg_type_t or a
mach_msg_type_long_t. The mach_msg_type_long_t type
descriptor allows larger values for some fields. The
msgtl_header field in the long descriptor is only used for its
inline, longform, and deallocate bits.
unsigned int and can be used to hold the
msgt_name component of the mach_msg_type_t and
mach_msg_type_long_t structure.
unsigned int and can be used to hold the
msgt_size component of the mach_msg_type_t and
mach_msg_type_long_t structure.
natural_t and can be used to hold the
msgt_number component of the mach_msg_type_t and
mach_msg_type_long_t structure.
unsigned int msgt_name : 8
msgt_name field specifies the data's type. The following
types are predefined:
MACH_MSG_TYPE_UNSTRUCTURED
MACH_MSG_TYPE_BIT
MACH_MSG_TYPE_BOOLEAN
MACH_MSG_TYPE_INTEGER_16
MACH_MSG_TYPE_INTEGER_32
MACH_MSG_TYPE_CHAR
MACH_MSG_TYPE_BYTE
MACH_MSG_TYPE_INTEGER_8
MACH_MSG_TYPE_REAL
MACH_MSG_TYPE_STRING
MACH_MSG_TYPE_STRING_C
MACH_MSG_TYPE_PORT_NAME
MACH_MSG_TYPE_PORT_NAME describes port right names, when no
rights are being transferred, but just names. For this purpose, it
should be used in preference to MACH_MSG_TYPE_INTEGER_32.
MACH_MSG_TYPE_MOVE_RECEIVE
MACH_MSG_TYPE_MOVE_SEND
MACH_MSG_TYPE_MOVE_SEND_ONCE
MACH_MSG_TYPE_COPY_SEND
MACH_MSG_TYPE_MAKE_SEND
MACH_MSG_TYPE_MAKE_SEND_ONCE
msgt_size : 8
msgt_size field specifies the size of each datum, in bits. For
example, the msgt_size of MACH_MSG_TYPE_INTEGER_32 data is 32.
msgt_number : 12
msgt_number field specifies how many data elements comprise
the data item. Zero is a legitimate number.
The total length specified by a type descriptor is (msgt_size *
msgt_number), rounded up to an integral number of bytes. In-line data
is then padded to an integral number of long-words. This ensures that
type descriptors always start on long-word boundaries. It implies that
message sizes are always an integral multiple of a long-word's size.
msgt_inline : 1
msgt_inline bit specifies, when FALSE, that the data
actually resides in an out-of-line region. The address of the memory
region (a vm_offset_t or vm_address_t) follows the type
descriptor in the message body. The msgt_name, msgt_size,
and msgt_number fields describe the memory region, not the
address.
msgt_longform : 1
msgt_longform bit specifies, when TRUE, that this type
descriptor is a mach_msg_type_long_t instead of a
mach_msg_type_t. The msgt_name, msgt_size, and
msgt_number fields should be zero. Instead, mach_msg uses
the following msgtl_name, msgtl_size, and
msgtl_number fields.
msgt_deallocate : 1
msgt_deallocate bit is used with out-of-line regions. When
TRUE, it specifies that the memory region should be deallocated
from the sender's address space (as if with vm_deallocate) when
the message is sent.
msgt_unused : 1
msgt_unused bit should be zero.
TRUE if the given type name specifies a port
type, otherwise it returns FALSE.
TRUE if the given type name specifies a port
type with a send or send-once right, otherwise it returns FALSE.
TRUE if the given type name specifies a port
right type which is moved, otherwise it returns FALSE.
mach_msg_type_t msgtl_header
msgt_header.
unsigned short msgtl_name
msgt_name.
unsigned short msgtl_size
msgt_size.
unsigned int msgtl_number
msgt_number.
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