================== OS Data Structures

Scalar Types

Many of the types used to communicate with NuttX are simple scalar types. These types are used to provide architecture independence of the OS from the application. The scalar types used at the NuttX interface include:

.. c:type:: pid_t .. c:type:: size_t .. c:type:: sigset_t .. c:type:: time_t

Hidden Interface Structures

Several of the types used to interface with NuttX are structures that are intended to be hidden from the application. From the standpoint of the application, these structures (and structure pointers) should be treated as simple handles to reference OS resources. These hidden structures include:

.. c:struct:: tcb_s .. c:type:: mqd_t .. c:type:: sem_t .. c:type:: pthread_key_t

In order to maintain portability, applications should not reference specific elements within these hidden structures. These hidden structures will not be described further in this user's manual.

Access to the errno Variable

A pointer to the thread-specific errno value is available through a function call:

.. c:function:: int *__errno(void)

__errno() returns a pointer to the thread-specific errno value. Note that the symbol errno is defined to be __errno() so that the usual access by referencing the symbol errno will work as expected.

.. code-block:: c

#include <errno.h>
#define errno *__errno()
int *__errno(void);

There is a unique, private errno value for each NuttX task. However, the implementation of errno differs somewhat from the use of errno in most multi-threaded process environments: In NuttX, each pthread will also have its own private copy of errno and the errno will not be shared between pthreads. This is, perhaps, non-standard but promotes better thread independence.

:return: A pointer to the thread-specific ``errno`` value.

User Interface Structures

.. c:type:: int (*main_t)(int argc, char *argv[])

:c:type:main_t defines the type of a task entry point. :c:type:main_t is declared in sys/types.h.

.. c:struct:: sched_param

This structure is used to pass scheduling priorities to and from NuttX:

.. code-block:: c

struct sched_param { int sched_priority; };

.. c:struct:: timespec

This structure is used to pass timing information between the NuttX and a user application:

.. code-block:: c

struct timespec { time_t tv_sec; /* Seconds / long tv_nsec; / Nanoseconds */ };

.. c:struct:: mq_attr

This structure is used to communicate message queue attributes between NuttX and a MoBY application:

.. code-block:: c

struct mq_attr { size_t mq_maxmsg; /* Max number of messages in queue / size_t mq_msgsize; / Max message size / unsigned mq_flags; / Queue flags / size_t mq_curmsgs; / Number of messages currently in queue */ };

.. note that this gives a warning due to https://github.com/sphinx-doc/sphinx/issues/7819 https://github.com/sphinx-doc/sphinx/pull/8313

.. c:struct:: sigaction

The following structure defines the action to take for given signal:

.. code-block:: c

struct sigaction { union { void (_sa_handler)(int); void (_sa_sigaction)(int, siginfo_t *, void *); } sa_u; sigset_t sa_mask; int sa_flags; }; #define sa_handler sa_u._sa_handler #define sa_sigaction sa_u._sa_sigaction

.. c:struct:: siginfo .. c:type:: siginfo_t

The following types is used to pass parameters to/from signal handlers:

.. code-block:: c

typedef struct siginfo { int si_signo; int si_code; union sigval si_value; } siginfo_t;

.. c:union:: sigval

This defines the type of the struct siginfo si_value field and is used to pass parameters with signals.

.. code-block:: c

union sigval { int sival_int; void *sival_ptr; };

.. c:struct:: sigevent

The following is used to attach a signal to a message queue to notify a task when a message is available on a queue.

.. code-block:: c

struct sigevent { int sigev_signo; union sigval sigev_value; int sigev_notify; };