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.. _posix_support:
POSIX Support
#############
The Portable Operating System Interface (POSIX) is a family of standards
specified by the IEEE Computer Society for maintaining compatibility between
operating systems. Zephyr implements a subset of the embedded profiles PSE51
and PSE52, and BSD Sockets API.
With the POSIX support available in Zephyr, an existing POSIX compliant
application can be ported to run on the Zephyr kernel, and therefore leverage
Zephyr features and functionality. Additionally, a library designed for use with
POSIX threading compatible operating systems can be ported to Zephyr kernel
based applications with minimal or no changes.
.. figure:: posix.svg
:align: center
:alt: POSIX Support in Zephyr
POSIX support in Zephyr
The POSIX API subset is an increasingly popular OSAL (operating system
abstraction layer) for IoT and embedded applications, as can be seen in
Zephyr, AWS:FreeRTOS, TI-RTOS, and NuttX.
Benefits of POSIX support in Zephyr include:
- Offering a familiar API to non-embedded programmers, especially from Linux
- Enabling reuse (portability) of existing libraries based on POSIX APIs
- Providing an efficient API subset appropriate for small (MCU) embedded systems
System Overview
===============
Units of Functionality
++++++++++++++++++++++
The system profile is defined in terms of component profiles that specify Units
of Functionality that can be combined to realize the application platform. A Unit
of Functionality is a defined set of services which can be implemented. If
implemented, the standard prescribes that all services in the Unit must
be implemented.
A Minimal Realtime System Profile implementation must support the
following Units of Functionality as defined in IEEE Std. 1003.1 (also referred to
as POSIX.1-2017).
.. csv-table:: Units of Functionality
:header: Requirements, Supported, Remarks
:widths: 50,10,60
POSIX_C_LANG_JUMP,
POSIX_C_LANG_SUPPORT,yes
POSIX_DEVICE_IO,
POSIX_FILE_LOCKING,
POSIX_SIGNALS,
POSIX_SINGLE_PROCESS,
POSIX_THREADS_BASE,yes
XSI_THREAD_MUTEX_EXT,yes
XSI_THREADS_EXT,yes
Option Requirements
++++++++++++++++++++
An implementation supporting the Minimal Realtime System
Profile must support the POSIX.1 Option Requirements which are defined in the
standard. Options Requirements are used for further sub-profiling within the
units of functionality: they further define the functional behavior of the
system service (normally adding extra functionality). Depending on the profile
to which the POSIX implementation complies,parameters and/or the precise
functionality of certain services may differ.
The following list shows the option requirements that are implemented in
Zephyr.
.. csv-table:: Option Requirements
:header: Requirements, Supported
:widths: 50,10
_POSIX_CLOCK_SELECTION,
_POSIX_FSYNC,
_POSIX_MEMLOCK,
_POSIX_MEMLOCK_RANGE,
_POSIX_MONOTONIC_CLOCK,
_POSIX_NO_TRUNC,
_POSIX_REALTIME_SIGNALS,
_POSIX_SEMAPHORES,yes
_POSIX_SHARED_MEMORY_OBJECTS,
_POSIX_SYNCHRONIZED_IO,
_POSIX_THREAD_ATTR_STACKADDR,
_POSIX_THREAD_ATTR_STACKSIZE,
_POSIX_THREAD_CPUTIME,
_POSIX_THREAD_PRIO_INHERIT,yes
_POSIX_THREAD_PRIO_PROTECT,
_POSIX_THREAD_PRIORITY_SCHEDULING,yes
_POSIX_THREAD_SPORADIC_SERVER,
_POSIX_TIMEOUTS,
_POSIX_TIMERS,
_POSIX2_C_DEV,
_POSIX2_SW_DEV,
Units of Functionality
======================
This section describes the Units of Functionality (fixed sets of interfaces)
which are implemented (partially or completely) in Zephyr. Please refer to the
standard for a full description of each listed interface.
POSIX_THREADS_BASE
+++++++++++++++++++
The basic assumption in this profile is that the system
consists of a single (implicit) process with multiple threads. Therefore, the
standard requires all basic thread services, except those related to
multiple processes.
.. csv-table:: POSIX_THREADS_BASE
:header: API, Supported
:widths: 50,10
pthread_atfork(),
pthread_attr_destroy(),yes
pthread_attr_getdetachstate(),yes
pthread_attr_getschedparam(),yes
pthread_attr_init(),yes
pthread_attr_setdetachstate(),yes
pthread_attr_setschedparam(),yes
pthread_cancel(),yes
pthread_cleanup_pop(),
pthread_cleanup_push(),
pthread_cond_broadcast(),yes
pthread_cond_destroy(),
pthread_cond_init(),yes
pthread_cond_signal(),yes
pthread_cond_timedwait(),yes
pthread_cond_wait(),yes
pthread_condattr_destroy(),
pthread_condattr_init(),
pthread_create(),yes
pthread_detach(),yes
pthread_equal(),
pthread_exit(),yes
pthread_getspecific(),yes
pthread_join(),yes
pthread_key_create(),yes
pthread_key_delete(),yes
pthread_kill(),
pthread_mutex_destroy(),yes
pthread_mutex_init(),yes
pthread_mutex_lock(),yes
pthread_mutex_trylock(),yes
pthread_mutex_unlock(),yes
pthread_mutexattr_destroy(),
pthread_mutexattr_init(),
pthread_once(),yes
pthread_self(),yes
pthread_setcalcelstate(),
pthread_setcanceltype(),
pthread_setspecific(),yes
pthread_sigmask(),
pthread_testcancel(),
XSI_THREAD_EXT
++++++++++++++
The XSI_THREADS_EXT Unit of Functionality is required because it provides
functions to control a thread's stack. This is considered useful for any
real-time application.
This table lists service support status in Zephyr:
.. csv-table:: XSI_THREAD_EXT
:header: API, Supported
:widths: 50,10
pthread_attr_getguardsize(),
pthread_attr_getstack(),yes
pthread_attr_setguardsize(),
pthread_attr_setstack(),yes
pthread_getconcurrency(),
pthread_setconcurrency()
XSI_THREAD_MUTEX_EXT
++++++++++++++++++++
The XSI_THREAD_MUTEX_EXT Unit of Functionality is required because it has
options for controlling the behavior of mutexes under erroneous application use.
This table lists service support status in Zephyr:
.. csv-table:: XSI_THREAD_MUTEX_EXT
:header: API, Supported
:widths: 50,10
pthread_mutexattr_gettype(),yes
pthread_mutexattr_settype(),yes
POSIX_C_LANG_SUPPORT
++++++++++++++++++++
The POSIX_C_LANG_SUPPORT Unit of Functionality contains the general ISO C
Library.
This is implemented as part of the minimal C library available in Zephyr.
.. csv-table:: POSIX_C_LANG_SUPPORT
:header: API, Supported
:widths: 50,10
abs(),yes
asctime(),
asctime_r(),
atof(),
atoi(),yes
atol(),
atoll(),
bsearch(),yes
calloc(),yes
ctime(),
ctime_r(),
difftime(),
div(),
feclearexcept(),
fegetenv(),
fegetexceptflag(),
fegetround(),
feholdexcept(),
feraiseexcept(),
fesetenv(),
fesetexceptflag(),
fesetround(),
fetestexcept(),
feupdateenv(),
free(),yes
gmtime(),yes
gmtime_r(),yes
imaxabs(),
imaxdiv(),
isalnum(),yes
isalpha(),yes
isblank(),
iscntrl(),
isdigit(),yes
isgraph(),yes
islower(),
isprint(),yes
ispunct(),
isspace(),yes
isupper(),yes
isxdigit(),yes
labs(),yes
ldiv(),
llabs(),yes
lldiv(),
localeconv(),
localtime(),yes
localtime_r(),
malloc(),yes
memchr(),yes
memcmp(),yes
memcpy(),yes
memmove(),yes
memset(),yes
mktime(),yes
qsort(),
rand(),yes
rand_r(),
realloc(),yes
setlocale(),
snprintf(),yes
sprintf(),yes
srand(),yes
sscanf(),
strcat(),yes
strchr(),yes
strcmp(),yes
strcoll(),
strcpy(),yes
strcspn(),
strerror(),yes
strerror_r(),yes
strftime(),
strlen(),yes
strncat(),yes
strncmp(),yes
strncpy(),yes
strpbrk(),
strrchr(),yes
strspn(),
strstr(),yes
strtod(),
strtof(),
strtoimax(),
strtok(),
strtok_r(),yes
strtol(),yes
strtold(),
strtoll(),yes
strtoul(),yes
strtoull(),yes
strtoumax(),
strxfrm(),
time(),yes
tolower(),yes
toupper(),yes
tzname(),
tzset(),
va_arg(),
va_copy(),
va_end(),
va_start(),
vsnprintf(),yes
vsprintf(),yes
vsscanf(),
POSIX_SINGLE_PROCESS
+++++++++++++++++++++
The POSIX_SINGLE_PROCESS Unit of Functionality contains services for single
process applications.
.. csv-table:: POSIX_SINGLE_PROCESS
:header: API, Supported
:widths: 50,10
confstr(),
environ,
errno,
getenv(),
setenv(),
sysconf(),
uname(),
unsetenv()
POSIX_SIGNALS
+++++++++++++
Signal services are a basic mechanism within POSIX-based systems and are
required for error and event handling.
.. csv-table:: POSIX_SIGNALS
:header: API, Supported
:widths: 50,10
abort(),yes
alarm(),
kill(),
pause(),
raise(),
sigaction(),
igaddset(),
sigdelset(),
sigemptyset(),
sigfillset(),
igismember(),
signal(),
sigpending(),
sigprocmask(),
igsuspend(),
sigwait()
POSIX_DEVICE_IO
+++++++++++++++
.. csv-table:: POSIX_DEVICE_IO
:header: API, Supported
:widths: 50,10
flockfile(),
ftrylockfile(),
funlockfile(),
getc_unlocked(),
getchar_unlocked(),
putc_unlocked(),
putchar_unlocked()
clearerr(),
close(),
fclose(),
fdopen(),
feof(),
ferror(),
fflush(),
fgetc(),
fgets(),
fileno(),
fopen(),
fprintf(),yes
fputc(),yes
fputs(),yes
fread(),
freopen(),
fscanf(),
fwrite(),yes
getc(),
getchar(),
gets(),
open(),yes
perror(),yes
printf(),yes
putc(),yes
putchar(),
puts(),yes
read(),yes
scanf(),
setbuf(),
etvbuf(),
stderr,
stdin,
stdout,
ungetc(),
vfprintf(),yes
vfscanf(),
vprintf(),yes
vscanf(),
write(),