Nick Garnett - Red Hat Inc.
Note: This is a draft document that is being distributed to gather public comments. Comments should be sent to the EL/IX discussion list athttp://sources.redhat.com/elix.
This website also provides access to the latest versions of this API specification together with other documents about EL/IX and archives of the mailing lists.
This document describes the proposed API for EL/IX . The goals for this API are:
EL/IX achieves these goals by identifying a subset of the POSIX.1 and ISO C standards, together with some extensions gleaned from Linux/GNU, BSD and SYSV, that are applicable to embedded applications. The result is an API that is somewhat smaller than the union of those standards that eliminates unnecessary or duplicated functionality fairly ruthlessly.
The following API levels are defined and each function in the API is assigned to a minimum level. Functions are present in that level and all higher levels.
The following option letters are added to the level numbers for some API functions when the presence of that function is also controlled by some other component (such as the presence of a file system), or is an optional component that not all implementations provide.
In some places this option is additionally annotated with sub-options (in square brackets) that indicate the properties that the file system must support for the given function.
In September 1999 the IEEE published standard 1003.13 ``Standardized Application Environment Profile - POSIX Realtime Application Support (AEP)''. This is a collection of four subsets of the POSIX.1 standard aimed at real time systems. This section examines the relationship between EL/IX and POSIX.13.
POSIX.13 presents four real time system profiles. The Minimal Realtime System Profile provides the basic set of functionality for a single process deeply embedded system. The Realtime Controller System Profile extends the minimal profile with support for a file system and asynchronous I/O. The Dedicated Realtime System Profile extends the minimal profile with support for multiple processes, but has more primitive support for file systems than the controller profile. Finally the Multi-Purpose Realtime System Profile is a superset of the other profiles and essentially consists of the entire POSIX.1, POSIX.1b and POSIX.1c standards.
These four profiles are superficially similar to our four levels although the controller and dedicated profiles are mutually exclusive in some areas. To ensure maximum compatibility, the EL/IX levels have been adjusted to allow each of the POSIX.13 profiles to be a complete subset of the closest matching level.
Each of the POSIX.13 profiles may be manufactured out of the matching EL/IX level by enabling certain options:
The Austin Common Standards Revision Group has been working on a revision of the POSIX standard that includes most of the subsidiary standards (1003.1j, Advanced Realtime Extensions, being the most relevant) together with the Open Group's Single UNIX Specification and ISO C99. This standard is due for delivery in Q2 2001. Based on a reading of Draft 4 (released August 2000) the EL/IX API has been adjusted to take this new standard into account. However, since much of the new functionality in POSIX 1003.1-200x does not yet appear in Linux, the EL/IX API remains, at present, a subset of that standard.
The base of EL/IX functionality is the POSIX.1003.1-1996 Specification (ISO/IEC 9945-1).
This document follows the sections of the POSIX.1 specification. The reader is referred to that document for details of the syntax and semantics of the functions described here.
| Function | Level | Options | Notes |
| fork() | 3 | ||
| execl() | 3 | ||
| execv() | 3 | ||
| execle() | 3 | ||
| execve() | 3 | ||
| execlp() | 3 | ||
| execvp() | 3 | ||
| pthread_atfork() | 3 |
| Function | Level | Options | Notes |
| wait() | 3 | ||
| waitpid() | 3 | ||
| _exit() | 3 |
Signals were introduced into UNIX as a mechanism for delivering exceptions and asynchronous events to single threaded processes. Like select() and poll() (see later) they are largely unnecessary in a multi-threaded environment. Additionally signal handling has subtle and pervasive effects on many parts of the POSIX standard, not all of which are relevant to, or implementable in, the kind of small footprint embedded operating system that is represented at level 1. Hence the exact functionality available at level 1 will depend on the capabilities of the underlying operating system.
These first few entries describe areas of functionality that are orthogonal to the actual functions.
| Function | Level | Options | Notes |
| Signal masks | 1 | s m o | 1 |
| EINTR wakeup | 1 | s m o | 2 |
| Notification mechanisms | 1 | s m o | 3 |
| Real time signals | 1 | s o | |
| Translate exceptions to signals | 1 | s m o | 4 |
| kill() | 1 | s m r | |
| sigemptyset() | 1 | s m r | |
| sigfillset() | 1 | s m r | |
| sigaddset() | 1 | s m r | |
| sigdelset() | 1 | s m r | |
| sigismember() | 1 | s m r | |
| sigaction() | 1 | s m r | |
| pthread_sigmask() | 1 | s m | 1 |
| sigprocmask() | 1 | s m r | |
| sigpending() | 1 | s m r | |
| sigsuspend() | 1 | s m r | |
| sigwait() | 1 | s m | |
| sigwaitinfo() | 1 | s m | |
| sigtimedwait() | 1 | s m | |
| sigqueue() | 1 | s m | 3 |
| pthread_kill() | 1 | s m | 1 |
Note 1: At level 1 signal delivery and masking may be restricted to operating at a global level only. Per-thread signal masks, and delivery of signals to specific threads may be restricted by the capabilities of the underlying operating system.
Note 2: This is the termination of many POSIX API calls on delivery of a signal to the thread or process. At level 1 this may require considerable extra code to safely terminate and clean up these functions. Thus this functionality is dependent on the implementation.
Note 3: Some signal-generating functions (timer expiration, asynchronous I/O, message arrival and sigqueue()), allow specification of an event notification mechanism using a sigevent structure. This allows the event to be notified either by delivery of a signal, or by the immediate invocation of a function in a new thread. At level 1, one or other of these mechanisms may not be present, depending on the ability of the operating system to deliver signals and its ability to create threads dynamically.
Note 4: If a level 1 operating system has the ability to catch synchronous exceptions (divide-by-zero, illegal instruction, FPU exceptions, address/alignment exceptions etc.) then it may be possible to translate these into POSIX signals for delivery to the current thread.
| Function | Level | Options | Notes |
| alarm() | 1 | s m r | |
| pause() | 1 | s m r | |
| sleep() | 1 | m |
Some of these may be useful to aid porting of existing code, hence they are not all just marked level 3 or 4.
| Function | Level | Options | Notes |
| getpid() | 1 | c | 1 |
| getppid() | 1 | c | 1 |
Note 1: At level 1 these functions simply return a constant value.
| Function | Level | Options | Notes |
| getuid() | 1 | c | 1 |
| geteuid() | 1 | c | 1 |
| getgid() | 1 | c | 1 |
| getegid() | 1 | c | 1 |
| setuid() | 4 | ||
| setgid() | 4 | ||
| getgroups() | 4 | ||
| getlogin() | 4 | ||
| getlogin_r() | 4 |
Note 1: At level 1 these functions simply return a constant value.
| Function | Level | Options | Notes |
| getpgrp() | 4 | ||
| setsid() | 4 | ||
| setpgid() | 4 |
| Function | Level | Options | Notes |
| uname() | 1 | m |
| Function | Level | Options | Notes |
| time() | 1 | r | |
| times() | 1 | m | 1 |
Note 1: At level 1 only some of the return values in the struct tms buffer will be filled in. At level 2 there will never be any child processes to be reported in the tms_cutime and tms_cstime fields.
Possibly have a configuration- or build- time defined static environment to support this.
| Function | Level | Options | Notes |
| getenv() | 1 |
| Function | Level | Options | Notes |
| ctermid() | 2 | t | |
| ttyname() | 2 | t | |
| ttyname_r() | 2 | t | |
| isatty() | 1 | f t n |
Under a level 1 operating system, only some of these variables will be implemented.
| Function | Level | Options | Notes |
| sysconf() | 1 | m r |
In many cases the functionality of these functions will be dictated by the properties of the underlying file system rather than by the operating system.
| Function | Level | Options | Notes |
| opendir() | 1 | f[d] m | |
| readdir() | 1 | f[d] m | |
| readdir_r() | 1 | f[d] m | |
| rewinddir() | 1 | f[d] m | |
| closedir() | 1 | f[d] m |
| Function | Level | Options | Notes |
| chdir() | 1 | f[d] | |
| getcwd() | 1 | f[d] o | 1 |
Note 1: The functionality of getcwd() may depend on the functionality of the underlying filing system. If the filesystem infrastructure does not track the current directory path, then finding the CWD requires either filesystem support for traversing the directory upwards, or the presence of ``..'' directory entries, neither of which are a given.
| Function | Level | Options | Notes |
| open() | 1 | f t m | 1 |
| creat() | 1 | f[m] | |
| umask() | 2 | f[mp] | |
| link() | 1 | f[ml] |
Note 1: At level 1 only a subset of the flags may be supported, and then only if the underlying file system or device provides support.
| Function | Level | Options | Notes |
| mkdir() | 1 | f[md] | |
| mkfifo() | 3 | o f[m] |
| Function | Level | Options | Notes |
| unlink() | 1 | f[m] | |
| rmdir() | 1 | f[md] | |
| rename() | 1 | f[m] |
| Function | Level | Options | Notes |
| stat() | 1 | f m | 1 |
| fstat() | 1 | f m | 1 |
| access() | 1 | f | |
| chmod() | 2 | f[mp] | |
| fchmod() | 2 | f[mp] | |
| chown() | 2 | f[mp] | |
| utime() | 2 | f | |
| ftruncate() | 4 | ||
| pathconf() | 2 | m | |
| fpathconf() | 2 | m |
Note 1: At level 1 some fields in the struct stat structure may not be filled in, this may also depend on the supporting file system.
As with the previous section, the properties of the underlying filesystems or devices will mostly dictate the functionality available here.
| Function | Level | Options | Notes |
| pipe() | 3 |
| Function | Level | Options | Notes |
| dup() | 1 | f t n | |
| dup2() | 1 | f t n | |
| close() | 1 | f t n |
| Function | Level | Options | Notes |
| read() | 1 | f t n | |
| write() | 1 | f t n |
| Function | Level | Options | Notes |
| fcntl() | 1 | m | 1 |
| lseek() | 1 | f |
Note 1: At level 1 only F_DUPFD need be supported. The remaining functionality depend mainly on the implementation of the underlying filesystem.
| Function | Level | Options | Notes |
| fsync() | 1 | f | |
| fdatasync() | 1 | f |
Completion of asynchronous IO operations is notified by invoking a sigevent object. In certain configurations this may be restricted to only specifying one of SIGEV_SIGNAL or SIGEV_THREAD as the notification type.
Asynchronous IO is largely unnecessary in a multi-threaded environment. Any implementation of these facilities may be expensive and exhibit poor performance. Hence this is an optional facility whose use is deprecated.
| Function | Level | Options | Notes |
| aio_read() | 1 | o f t n | |
| aio_write() | 1 | o f t n | |
| lio_listio() | 1 | o f t n | |
| aio_error() | 1 | o f t n | |
| aio_return() | 1 | o f t n | |
| aio_cancel() | 1 | o f t n | |
| aio_suspend() | 1 | o f t n | |
| aio_fsync() | 1 | o f t n |
These are only present to control the behaviour of a serial line. Even then, most of the line editing and translation functionality will be omitted ( at level 1 at least ) and all job control functionality is banished to level 4.
| Function | Level | Options | Notes |
| tcgetattr() | 1 | t | |
| tcsetattr() | 1 | t | |
| cfgetospeed() | 1 | t | |
| cfgetispeed() | 1 | t | |
| cfsetospeed() | 1 | t | |
| cfsetispeed() | 1 | t | |
| tcsendbreak() | 1 | t | |
| tcdrain() | 1 | t | |
| tcflush() | 1 | t | |
| tcflow() | 1 | t | |
| tcgetpgrp() | 4 | ||
| tcsetpgrp() | 4 |
POSIX specified modifications and enhancements to the ISO C API.
| Function | Level | Options | Notes |
| setlocale() | 1 | l | 1 |
| fileno() | 1 | f t n | |
| fdopen() | 1 | f t n | |
| flockfile() | 1 | ||
| ftrylockfile() | 1 | ||
| funlockfile() | 1 | ||
| getc_unlocked() | 1 | ||
| getchar_unlocked() | 1 | ||
| putc_unlocked() | 1 | ||
| putchar_unlocked() | 1 | ||
| sigsetjmp() | 1 | s r | |
| siglongjmp() | 1 | s r | |
| tzset() | 1 | o | 1 |
| strtok_r() | 1 | ||
| asctime_r() | 1 | ||
| ctime_r() | 1 | ||
| gmtime_r() | 1 | ||
| localtime_r() | 1 | ||
| rand_r() | 1 |
Note 1: Locale support may be limited to just the ``C'' locale and maybe the ``POSIX'' locale.
Note 2: At level 1, and maybe others, only a very reduced time zone implementation need be provided. This will probably rely on external information (such as configuration-, build-, install-time options or user input) to determine the UTC offset, DST change dates and time zone abbreviations.
Access to group and password databases.
| Function | Level | Options | Notes |
| getgrgid() | 4 | ||
| getgrgid_r() | 4 | ||
| getgrnam() | 4 | ||
| getgrnam_r() | 4 | ||
| getpwuid() | 4 | ||
| getpwuid_r() | 4 | ||
| getpwnam() | 4 | ||
| getpwnam_r() | 4 |
This section of POSIX.1 describes the tar and cpio formats for data archives. These are irrelevant for embedded applications.
| Function | Level | Options | Notes |
| sem_init() | 1 | r | |
| sem_destroy() | 1 | r | |
| sem_open() | 4 | 1 | |
| sem_close() | 4 | 1 | |
| sem_unlink() | 4 | 1 | |
| sem_wait() | 1 | r | |
| sem_trywait() | 1 | r | |
| sem_post() | 1 | r | |
| sem_getvalue() | 1 | r |
Note 1: These functions can be supplied at lower levels if kernel support is present, or if a fake namespace for them to operate in is implemented.
| Function | Level | Options | Notes |
| pthread_mutexattr_init() | 1 | r | |
| pthread_mutexattr_destroy() | 1 | r | |
| pthread_mutexattr_getpshared() | 3 | r | |
| pthread_mutexattr_setpshared() | 3 | r | |
| pthread_mutex_init() | 1 | r | |
| pthread_mutex_destroy() | 1 | r | |
| pthread_mutex_lock() | 1 | r | |
| pthread_mutex_trylock() | 1 | r | |
| pthread_mutex_unlock() | 1 | r |
| Function | Level | Options | Notes |
| pthread_condattr_init() | 1 | r | |
| pthread_condattr_destroy() | 1 | r | |
| pthread_condattr_getpshared() | 3 | r | |
| pthread_condattr_setpshared() | 3 | r | |
| pthread_cond_init() | 1 | r | |
| pthread_cond_destroy() | 1 | r | |
| pthread_cond_signal() | 1 | r | |
| pthread_cond_broadcast() | 1 | r | |
| pthread_cond_wait() | 1 | r | |
| pthread_cond_timedwait() | 1 | r |
| Function | Level | Options | Notes |
| mlockall() | 1 | M[l] | |
| munlockall() | 1 | M[l] | |
| mlock() | 1 | M[l] | |
| munlock() | 1 | M[l] | |
| mmap() | 1 | M[fo] | |
| munmap() | 1 | M[fo] | |
| mprotect() | 2 | M[p] | |
| msync() | 2 | M[f] |
| Function | Level | Options | Notes |
| shm_open() | 1 | M[op] | |
| shm_unlink() | 1 | M[o] |
At level 1 we define SCHED_OTHER to equal SCHED_RR. This equality is allowed by POSIX.1.
| Function | Level | Options | Notes |
| sched_setparam() | 3 | r | |
| sched_getparam() | 3 | r | |
| sched_setscheduler() | 3 | r | |
| sched_getscheduler() | 3 | r | |
| sched_yield() | 1 | r | |
| sched_get_priority_max() | 1 | r | |
| sched_get_priority_min() | 1 | r | |
| sched_rr_get_interval() | 1 | r |
| Function | Level | Options | Notes |
| pthread_attr_setscope() | 1 | r | 1 |
| pthread_attr_getscope() | 1 | r | 1 |
| pthread_attr_setinheritsched() | 1 | r | |
| pthread_attr_getinheritsched() | 1 | r | |
| pthread_attr_setschedpolicy() | 1 | r | |
| pthread_attr_getschedpolicy() | 1 | r | |
| pthread_attr_setschedparam() | 1 | r | |
| pthread_attr_getschedparam() | 1 | r | |
| pthread_getschedparam() | 1 | r | |
| pthread_setschedparam() | 1 | r |
Note 1: At levels 1 and 2 only the only scope permitted may be PTHREAD_SCOPE_SYSTEM.
At level 1, depending on the capabilities of the underlying operating system, one or both of PTHREAD_PRIO_INHERIT or PTHREAD_PRIO_PROTECT may not be implemented.
| Function | Level | Options | Notes |
| pthread_mutexattr_setprotocol() | 1 | r | |
| pthread_mutexattr_getprotocol() | 1 | r | |
| pthread_mutexattr_setprioceiling() | 1 | r | |
| pthread_mutexattr_getprioceiling() | 1 | r | |
| pthread_mutex_setprioceiling() | 1 | r | |
| pthread_mutex_getprioceiling() | 1 | r |
Note that timers indicate that they have expired by raising a signal. This implies that some form of signal support be present all the time, or that the presence of timers is also dependent on the presence of signal handling. Alternatively, the sigevent structure supplied to timer_create() may only specify SIGEV_THREAD as the notification type.
There is also some question over the presence of these functions in current Linux releases.
| Function | Level | Options | Notes |
| clock_settime() | 1 | r | |
| clock_gettime() | 1 | r | |
| clock_getres() | 1 | r | |
| timer_create() | 1 | s r | |
| timer_delete() | 1 | s r | |
| timer_settime() | 1 | s r | |
| timer_gettime() | 1 | s r | |
| timer_getoverrun() | 1 | s r | |
| nanosleep() | 1 | r |
These are more oriented towards inter-process communications rather than intra-process, where the program should be using semaphores, mutexes etc. At level 1 it may be necessary to provide a fake name space for the mq_open(), and mq_unlink() functions to work within.
| Function | Level | Options | Notes |
| mq_open() | 1 | r o | |
| mq_close() | 1 | r o | |
| mq_unlink() | 1 | r o | |
| mq_send() | 1 | r o | |
| mq_receive() | 1 | r o | |
| mq_notify() | 1 | r o | |
| mq_setattr() | 1 | r o | |
| mq_getattr() | 1 | r o |
| Function | Level | Options | Notes |
| pthread_attr_init() | 1 | r | |
| pthread_attr_destroy() | 1 | r | |
| pthread_attr_setstacksize() | 1 | r | |
| pthread_attr_getstacksize() | 1 | r | |
| pthread_attr_setstackaddr() | 1 | r | |
| pthread_attr_getstackaddr() | 1 | r | |
| pthread_attr_setdetachstate() | 1 | r | |
| pthread_attr_getdetachstate() | 1 | r | |
| pthread_create() | 1 | r | |
| pthread_join() | 1 | r | |
| pthread_detach() | 1 | r | |
| pthread_exit() | 1 | r | |
| pthread_self() | 1 | r | |
| pthread_equal() | 1 | r | |
| pthread_once() | 1 | r |
| Function | Level | Options | Notes |
| pthread_key_create() | 1 | r | |
| pthread_setspecific() | 1 | r | |
| pthread_getspecific() | 1 | r | |
| pthread_key_delete() | 1 | r |
At level 1, one or both of PTHREAD_CANCEL_ASYNCHRONOUS and PTHREAD_CANCEL_DEFERRED may not be implemented, depending on the capabilities of the underlying operating system.
| Function | Level | Options | Notes |
| pthread_cancel() | 1 | o r | |
| pthread_setcancelstate() | 1 | o r | |
| pthread_setcanceltype() | 1 | o r | |
| pthread_testcancel() | 1 | o r | |
| pthread_cleanup_push() | 1 | o r | |
| pthread_cleanup_pop() | 1 | o r |
The list of functions here is based the documentation for Glibc V2.1, cross checked with the Linux headers and the ISO C 1999 standard.
A slight difficulty with non-ISO C-standard functionality here is that while on Linux glibc is available, it is not always available on an embedded operating system due to the viral nature of GPL. The demands of Linux compatibility require the C library functionality to be compatible with Glibc, which is primarily ISO C99 compatible. However, the C libraries for many embedded operating systems are only ISO C89 compatible, and much that is present in C99 is not applicable to an embedded environment. Hence at level 1 only C89 compatibility is required, although if C99 compatibility is available it may be used. The distribution of functionality between levels 1 and 2 attempts to this into account.
Where the phrase ``ISO C'' is used in this document it should usually be read as ``ISO C89'' at level 1 and ``ISO C99'' at higher levels.
Conversion of error codes to strings: strerror() and perror(). strerror_r() is a GNU extension.
The main problem with these functions is the memory needed to store the array of strings, hence these must be optional.
| Function | Level | Options | Notes |
| strerror() | 1 | o l | |
| strerror_r() | 1 | o l | |
| perror() | 1 | o l |
Only the first four of these are ISO C, the rest are GNU or X/Open extensions.
| Function | Level | Options | Notes |
| malloc() | 1 | ||
| free() | 1 | ||
| realloc() | 1 | ||
| calloc() | 1 | ||
| memalign() | 2 | ||
| valloc() | 2 | ||
| pvalloc() | 2 | ||
| mallopt() | 2 | ||
| mcheck() | 2 | ||
| mprobe() | 2 | ||
| mallinfo() | 1 |
ISO C character classification functions, plus GNU extension isblank() and BSD/SVID extension isascii().
| Function | Level | Options | Notes |
| ISO C functions | 1 | l | |
| isblank() | 2 | l o | |
| isascii() | 2 | l o |
ISO C case conversion functions plus BSD/SVID toascii() and SVID _tolower() and _toupper().
| Function | Level | Options | Notes |
| ISO C functions | 1 | l | |
| toascii() | 2 | l o | |
| _tolower() | 2 | l o | |
| _toupper() | 2 | l o |
ISO C wide character classification functions, plus GNU extension iswblank().
| Function | Level | Options | Notes |
| ISO C functions | 2 | l | |
| iswblank() | 2 | l o |
ISO C wide character case conversion functions.
| Function | Level | Options | Notes |
| ISO C functions | 2 | l o |
ISO C strlen() plus GNU strnlen() extension.
| Function | Level | Options | Notes |
| strlen() | 1 | l | |
| strnlen() | 1 | l o |
ISO C mem* and str* copy functions plus some GNU extensions and some BSD compatibility functions such as bcopy().
| Function | Level | Options | Notes |
| ISO C functions | 1 | l | |
| mempcpy() | 2 | l o | |
| memccpy() | 2 | l o | |
| strdup() | 2 | l o | |
| strndup() | 2 | l o | |
| bcopy() | 1 | l | |
| bzero() | 1 | l |
ISO C mem* and str* copy functions plus some GNU extensions and some BSD compatibility functions.
| Function | Level | Options | Notes |
| ISO C functions | 1 | l | |
| strcasecmp() | 2 | l o | |
| strncasecmp() | 2 | l o | |
| bcmp() | 2 | l o |
ISO C collation functions strcoll() and strxfrm().
| Function | Level | Options | Notes |
| strcoll() | 1 | l | |
| strxfrm() | 1 | l |
ISO C mem* and str* search functions.
| Function | Level | Options | Notes |
| ISO C functions | 1 | l |
ISO C strtok() and BSD extension strsep().
| Function | Level | Options | Notes |
| strtok() | 1 | l | |
| strsep() | 1 | l |
| Function | Level | Options | Notes |
| l64a() | 2 | l | |
| a64l() | 2 | l |
Various functions for manipulating argv[][] style arrays and derived environment string arrays. These will be needed if support for getenv() and especially putenv() is present.
| Function | Level | Options | Notes |
| argz_create() | 2 | l | |
| argz_create_sep() | 2 | l | |
| argz_count() | 2 | l | |
| argz_extract() | 2 | l | |
| argz_stringify() | 2 | l | |
| argz_add() | 2 | l | |
| argz_add_sep() | 2 | l | |
| argz_append() | 2 | l | |
| argz_delete() | 2 | l | |
| argz_insert() | 2 | l | |
| argz_next() | 2 | l | |
| argz_replace() | 2 | l | |
| envz_entry() | 2 | l | |
| envz_get() | 2 | l | |
| envz_add() | 2 | l | |
| envz_merge() | 2 | l | |
| envz_strip() | 2 | l |
Various ISO C and X/Open mechanisms for handling multibyte character conversions.
| Function | Level | Options | Notes |
| ISO C functions | 2 | l | |
| X/Open functions | 2 | l |
ISO C and X/Open functions for setting and querying the locale.
At level 1 only support for the "C" locale is required, and maybe the "POSIX" one, if that ever differs from "C".
| Function | Level | Options | Notes |
| ISO C functions | 1 | l | |
| X/Open functions | 2 | l |
X/Open ``catgets'' and GNU ``gettext'' facilities for translating messages into different languages.
| Function | Level | Options | Notes |
| X/Open ``catgets'' functions | 2 | l | |
| GNU ``gettext'' functions | 2 | l |
ISO C bsearch() and qsort() functions plus GNU extensions for hash and tree sort/search.
| Function | Level | Options | Notes |
| bsearch() | 1 | l | |
| qsort() | 1 | l | |
| hcreate() | 2 | l | |
| hdestroy() | 2 | l | |
| hsearch() | 2 | l | |
| hcreate_r() | 2 | l | |
| hdestroy_r() | 2 | l | |
| hsearch_r() | 2 | l | |
| tsearch() | 2 | l | |
| tfind() | 2 | l | |
| tdelete() | 2 | l | |
| tdestroy() | 2 | l | |
| twalk() | 2 | l |
Various GNU-only extensions for wildcards, globbing and regular expression matching.
| Function | Level | Options | Notes |
| fnmatch() | 2 | l | |
| glob() | 2 | l | |
| globfree() | 2 | l | |
| regcomp() | 2 | l | |
| regexec() | 2 | l | |
| regfree() | 2 | l | |
| regerror() | 2 | l | |
| wordexp() | 2 | l | |
| wordfree() | 2 | l |
These are mostly the ISO C set plus some GNU, BSD and SYSV extensions. None of these are necessary if we don't have any devices, file systems or network stacks to use them with.
| Function | Level | Options | Notes |
| fopen() | 1 | ||
| fopen64() | 2 | ||
| freopen() | 1 | ||
| freopen64() | 2 | ||
| fclose() | 1 | ||
| fcloseall() | 2 |
| Function | Level | Options | Notes |
| fputc() | 1 | ||
| putc() | 1 | ||
| putchar() | 1 | ||
| fputs() | 1 | ||
| puts() | 1 | ||
| putw() | 2 | ||
| fgetc() | 1 | ||
| getc() | 1 | ||
| getchar() | 1 | ||
| getw() | 2 | ||
| getline() | 2 | ||
| getdelim() | 2 | ||
| fgets() | 1 | ||
| gets() | 1 | ||
| ungetc() | 1 |
| Function | Level | Options | Notes |
| fread() | 1 | ||
| fwrite() | 1 |
The main option on all of these would be to drop the floating point formats to produce an integer only implementation.
| Function | Level | Options | Notes |
| printf() | 1 | m | |
| fprintf() | 1 | m | |
| sprintf() | 1 | m | |
| snprintf() | 1 | m | |
| asprintf() | 2 | m | |
| vprintf() | 1 | m | |
| vfprintf() | 1 | m | |
| vsprintf() | 1 | m | |
| vsnprintf() | 1 | m | |
| vasprintf() | 2 | m | |
| obstack_printf() | 4 | m | |
| obstack_vprintf() | 4 | ||
| parse_printf_format() | 4 |
As with the output functions, the floating point formats in these functions are optional.
| Function | Level | Options | Notes |
| scanf() | 1 | m | |
| fscanf() | 1 | m | |
| sscanf() | 1 | m | |
| vscanf() | 1 | m | |
| vfscanf() | 1 | m | |
| vsscanf() | 1 | m |
| Function | Level | Options | Notes |
| clearerr() | 1 | ||
| feof() | 1 | ||
| ferror() | 1 |
| Function | Level | Options | Notes |
| ftell() | 1 | ||
| ftello() | 2 | ||
| ftello64() | 2 | ||
| fseek() | 1 | ||
| fseeko() | 2 | ||
| fseeko64() | 2 | ||
| rewind() | 1 | ||
| fgetpos() | 1 | ||
| fgetpos64() | 2 | ||
| fsetpos() | 1 | ||
| fsetpos64() | 2 |
| Function | Level | Options | Notes |
| fflush() | 1 | ||
| setvbuf() | 1 | ||
| setbuf() | 1 | ||
| setbuffer() | 1 | ||
| setlinebuf() | 1 |
| Function | Level | Options | Notes |
| fmemopen() | 4 | ||
| open_memstream() | 4 | ||
| open_obstack_stream() | 4 | ||
| fopencookie() | 4 | ||
| fmtmsg() | 4 | ||
| addseverity() | 4 |
Most of these functions are also covered by POSIX. Listed here are just those that are extensions to POSIX.
| Function | Level | Options | Notes |
| open64() | 2 | ||
| truncate() | 4 | ||
| truncate64() | 4 | ||
| ftruncate64() | 4 | ||
| pread() | 1 | ||
| pread64() | 2 | ||
| pwrite() | 1 | ||
| pwrite64() | 2 | ||
| lseek64() | 1 | ||
| fclean() | 2 | ||
| readv() | 2 | ||
| writev() | 2 | ||
| mremap() | 2 | ||
| select() | 1 | c m o | 1 |
| poll() | 1 | c m o | 1 |
| sync() | 1 | ||
| ioctl() | 1 | c m o |
Note 1: select() and poll() were invented to enable single-thread UNIX processed to handle multiple events. Neither is at all necessary in a multi-threaded environment. If present they will exist only to support the porting of existing code, and may be severely limited in their applicability and performance. Use of these functions is deprecated.
| Function | Level | Options | Notes |
| aio_read64() | 2 | ||
| aio_write64() | 2 | ||
| lio_listio64() | 2 | ||
| aio_error64() | 2 | ||
| aio_return64() | 2 | ||
| aio_fsync64() | 2 | ||
| aio_suspend64() | 2 | ||
| aio_cancel64() | 2 | ||
| aio_init() | 4 |
Again, some of these are already defined by POSIX.
| Function | Level | Options | Notes |
| getwd() | 2 | f[d] c | |
| telldir() | 2 | f[d] | |
| seekdir() | 2 | f[d] | |
| scandir() | 2 | f[d] | |
| alphasort() | 2 | f[d] | |
| versionsort() | 2 | f[d] | |
| scandir64() | 2 | f[d] | |
| alphasort64() | 2 | f[d] | |
| versionsort64() | 2 | f[d] | |
| ftw() | 2 | f[d] | |
| ftw64() | 2 | f[d] | |
| nftw() | 2 | f[d] | |
| nftw64() | 2 | f[d] |
| Function | Level | Options | Notes |
| symlink() | 2 | f[ml] | |
| readlink() | 2 | f[l] | |
| remove() | 1 | f[m] | |
| mknod() | 4 | f[m] |
| Function | Level | Options | Notes |
| stat64() | 2 | f | |
| fstat64() | 2 | f | |
| lstat() | 2 | f[l] | |
| lstat64() | 2 | f[l] | |
| fchown() | 2 | f[mp] | |
| getumask() | 2 | f[p] | |
| utimes() | 2 | f |
| Function | Level | Options | Notes |
| tmpfile() | 1 | f[m] | |
| tmpfile64() | 2 | f[m] | |
| tmpnam() | 1 | f[m] | |
| tmpnam_r() | 1 | f[m] | |
| tempnam() | 2 | f[m] | |
| mktemp() | 2 | f[m] | |
| mkstemp() | 2 | f[m] |
| Function | Level | Options | Notes |
| popen() | 4 | ||
| pclose() | 4 |
The database access functions here should probably have configurations that allow them to work from memory based tables or "string files" rather than real files. These functions are also all marked as optional at level 1 since their functionality is often not required in an embedded system.
| Function | Level | Options | Notes |
| socket() | 1 | n | |
| bind() | 1 | n | |
| getsockname() | 1 | n | |
| shutdown() | 1 | n | |
| socketpair() | 1 | n | |
| connect() | 1 | n | |
| listen() | 1 | n | |
| accept() | 1 | n | |
| getpeername() | 1 | n | |
| send() | 1 | n | |
| recv() | 1 | n | |
| sendto() | 1 | n | |
| recvfrom() | 1 | n | |
| getsockopt() | 1 | n | |
| setsockopt() | 1 | n |
| Function | Level | Options | Notes |
| inet_aton() | 1 | n | |
| inet_addr() | 1 | n | |
| inet_network() | 1 | n | |
| inet_ntoa() | 1 | n | |
| inet_makeaddr() | 1 | n | |
| inet_lnaof() | 1 | n | |
| inet_netof() | 1 | n | |
| inet_pton() | 1 | n | |
| inet_ntop() | 1 | n |
| Function | Level | Options | Notes |
| gethostbyname() | 1 | n o | |
| gethostbyname2() | 1 | n o | |
| gethostbyaddr() | 1 | n o | |
| sethostent() | 1 | n o | |
| gethostent() | 1 | n o | |
| endhostent() | 1 | n o |
| Function | Level | Options | Notes |
| getprotobyname() | 1 | n o | |
| getprotobynumber() | 1 | n o | |
| setprotoent() | 1 | n o | |
| getprotoent() | 1 | n o | |
| endprotoent() | 1 | n o |
| Function | Level | Options | Notes |
| getservbyname() | 1 | n o | |
| getservbyport() | 1 | n o | |
| setservent() | 1 | n o | |
| getservent() | 1 | n o | |
| endservent() | 1 | n o |
| Function | Level | Options | Notes |
| getnetbyname() | 1 | n o | |
| getnetbyaddr() | 1 | n o | |
| setnetent() | 1 | n o | |
| getnetent() | 1 | n o | |
| endnetent() | 1 | n o |
| Function | Level | Options | Notes |
| htons() | 1 | n | |
| ntohs() | 1 | n | |
| htonl() | 1 | n | |
| ntohl() | 1 | n |
| Function | Level | Options | Notes |
| if_nametoindex() | 4 | ||
| if_indextoname() | 4 | ||
| if_nameindex() | 4 | ||
| if_freenameindex() | 4 |
| Function | Level | Options | Notes |
| cfmakeraw() | 4 | ||
| pseudo-terminal functions | 4 |
The usual collection of trig, exponent, hyperbolic and random number functions, too many to list here, look at the ISO C standard for a full list.
| Function | Level | Options | Notes |
| ISO C89 functions | 1 | l | |
| ISO C99 functions | 1 | l o | |
| GNU extensions | 2 | l o |
ISO C floating point arithmetic and FPU control functions plus some extensions.
| Function | Level | Options | Notes |
| ISO C89 functions | 1 | l | |
| ISO C99 functions | 1 | l o | |
| GNU extensions | 2 |
Full time zone support can be very large in code and data sizes. At levels 1 and 2 a considerably reduced implementation may be provided.
| Function | Level | Options | Notes |
| clock() | 1 | ||
| difftime() | 1 | ||
| gettimeofday() | 1 | ||
| settimeofday() | 1 | ||
| adjtime() | 4 | ||
| localtime() | 1 | ||
| gmtime() | 1 | ||
| mktime() | 1 | ||
| asctime() | 1 | ||
| ctime() | 1 | ||
| strftime() | 1 | ||
| strptime() | 1 | ||
| getdate() | 1 | ||
| getdate_r() | 1 | ||
| ntp_gettime() | 1 | n o | |
| ntp_adjtime() | 1 | n o | |
| setitimer() | 1 | m o | |
| getitimer() | 1 | m o |
| Function | Level | Options | Notes |
| getrusage() | 1 | m o | |
| getrlimit() | 1 | m o | |
| getrlimit64() | 2 | m | |
| setrlimit() | 2 | m | |
| setrlimit64() | 2 | m |
| Function | Level | Options | Notes |
| setjmp() | 1 | ||
| longjmp() | 1 |
Many of these are obsolete or alternative interfaces to the basic POSIX signal functionality. Use of these should be replaced where necessary by the POSIX functions.
strsignal() and psignal() share the same problems as strerror() and perror() in needing RAM to store the strings table.
| Function | Level | Options | Notes |
| strsignal() | 1 | o m | |
| psignal() | 1 | o m | |
| signal() | 1 | c | 1 |
| raise() | 1 | c | 2 |
| sysv_signal() | 4 | ||
| ssignal() | 4 | ||
| gsignal() | 4 | ||
| killpg() | 4 | ||
| sigaltstack() | 4 | ||
| sigstack() | 4 | ||
| sigvec() | 4 | ||
| siginterrupt() | 4 | ||
| sigblock() | 4 | ||
| sigsetmask() | 4 | ||
| sigpause() | 4 |
Note 1: This is merely a wrapper for sigaction().
Note 2: This is merely a wrapper for kill().
| Function | Level | Options | Notes |
| getopt() | 2 | l | |
| getopt_long() | 2 | l | |
| argp_parse() | 2 | l | |
| argp_help() | 2 | l | |
| getsubopt() | 2 | l |
The only real use for changing the environment is to prepare it for passing on to a sub-process. Hence these functions are only necessary at level 3.
| Function | Level | Options | Notes |
| putenv() | 3 | ||
| setenv() | 3 |
| Function | Level | Options | Notes |
| exit() | 1 | ||
| atexit() | 1 | ||
| on_exit() | 2 | ||
| abort() | 1 | ||
| _Exit() | 1 |
| Function | Level | Options | Notes |
| system() | 4 | ||
| vfork() | 4 | ||
| wait3() | 4 | ||
| wait4() | 4 | ||
| getpriority() | 4 | ||
| setpriority() | 4 | ||
| nice() | 4 |
| Function | Level | Options | Notes |
| setreuid() | 4 | ||
| setregid() | 4 | ||
| setgroups() | 4 | ||
| initgroups() | 4 | ||
| GNU, BSD and X/Open extensions | 4 |
| Function | Level | Options | Notes |
| gethostname() | 1 | n | |
| sethostname() | 1 | n | |
| gethostid() | 1 | n | |
| sethostid() | 1 | n | |
| fstab access functions | 2 | f | |
| mtab access functions | 2 | f |
| Function | Level | Options | Notes |
| confstr() | 2 | o |
Some embedded applications will need cryptographic security. However the DES based encryption provided by these functions is probably inadequate and has various legal problems. Those applications that need it will probably pick up a stronger, legal, encryption package elsewhere. Hence these functions are entirely optional.
| Function | Level | Options | Notes |
| getpass() | 4 | ||
| crypt() | 1 | l o | |
| crypt_r() | 1 | l o | |
| setkey() | 1 | l o | |
| encrypt() | 1 | l o | |
| setkey_r() | 1 | l o | |
| encrypt_r() | 1 | l o | |
| ecb_crypt() | 1 | l o | |
| cbc_crypt() | 1 | l o | |
| des_setparity() | 1 | l o |
The following are LinuxThreads extensions.
| Function | Level | Options | Notes |
| pthread_cleanup_push_defer_np() | 2 | ||
| pthread_cleanup_pop_restore_np() | 2 | ||
| pthread_mutexattr_setkind_np() | 2 | ||
| pthread_mutexattr_getkind_np() | 2 | ||
| pthread_kill_other_threads_np() | 2 |