PORTABILITY(7)

NAME
portability - standard library portability information

DESCRIPTION
This manual documents replacements for interfaces not available in the standard library or with special portability notes.

Software written for other operating systems can be ported by replacing uses of obsolete interfaces with the modern replacements and working around any missing functionality. The standard library attemps to implement the relevant parts of the C and POSIX standards with useful extensions and tends to omit non-standard extensions found on other operating systems whenever standard interfaces exists.

  alloca
alloca(3) and variable length arrays are implemented by the compiler, however the main thread stack size is fixed and does not grow unlike other operating systems, and large stack uses should instead use malloc(3) or set the stack size explicitly for another thread using pthread_attr_setstacksize(2).

  asctime, asctime_r
strftime(3) is the standard replacement.

  bcopy
memcpy(3) is the standard replacement. Note how the order of the source and destination parameters is swapped.

  bzero
memset(3) is the standard replacement.

  caddr_t
void * is the standard type.

  clock
clock(3) is implemented but can overflow, and clock_gettime(2) CLOCK_PROCESS_CPUTIME_ID is the modern replacement with nanosecond precision.

  ctime, ctime_r
strftime(3) is the standard replacement.

  daemon
Daemons should not background by double forking but rather stay in the foreground as described in daemon(7) and be managed by init(8).

  __dead
noreturn from <stdnoreturn.h> is the modern standard replacement or the __attribute__((noreturn)) extension can be used.

  flock, fcntl F_UNLCK, F_WRLCK, F_GETLK, F_SETLK, F_SETLKW, lockf
POSIX advisory locks are not implemented due to their flawed design of being process-wide instead of being per file description. The superior flock(2) is not currently implemented. It might be safe enough to omit the file locking as a workaround.

  ftime
clock_gettime(2) is the standard replacement.

  getdtablesize
The file descriptor table is unbounded and file descriptors above a certain value can be closed using closefrom(2) and iterated using psctl(2).

  getgroups, setgroups, initgroups
Supplementary groups are not implemented yet. It may be possible to remove invocations as a workaround.

  gethostbyaddr
getnameinfo(3) is the standard modern replacement.

  gethostbyname
getaddrinfo(3) is the standard modern replacement.

  getitimer, setitimer
timer_create(2) is the modern standard replacement.

  getpgrp, setpgrp
getpgid(3) and setpgid(3) are the standard portable replacements without disagreement on the function signatures.

  gettimeofday
gettimeofday(2) is implemented but the second parameter is defunct and is typed void * per POSIX instead of struct timezone *. clock_gettime(2) is the modern replacement with nanosecond precision.

  gid_t
gid_t is 64-bit unsigned and can be formatted portably cast to a uintmax_t using “%ju”.

  inet_addr, inet_aton
inet_pton(3) and getaddrinfo(3) are the modern standard replacements, however they don't support the unusual IPv4 notations.

  inet_ntoa
inet_ntop(3) and getnameinfo(3) are the modern standard replacements.

  <limits.h>
<limits.h> is currently implemented by the compiler instead of the standard library and it does not define everything required by POSIX. <sortix/limits.h> can be included instead as a temporary workaround if the required definitions are absent.

  makedev, major, minor
The kernel does not have a concept of major and minor device numbers.

  mkfifo
mkfifo(2) named pipes are not currently implemented but unnamed pipes are available using pipe(2), or alternatively AF_UNIX sockets can be used instead.

  mknod
Devices in the /dev filesystem are created by the kernel and cannot be manually created.

  mmap
mmap(2) is implemented, but MAP_SHARED shared memory mappings are not implemented yet.

  off_t
off_t is 64-bit signed and can be formatted portably cast to an intmax_t using “%jd”.

  PATH_MAX
The PATH_MAX limit does not currently exist and may be added in the future. Applications should be written as if this limit does not exist, but if required, it can be defined to 4096 as a fallback.

  pid_t
pid_t is 64-bit signed and can be formatted portably cast to an intmax_t using “%jd”.

  poll
poll(2) is implemented in <poll.h> per POSIX, however some operating systems have a <sys/poll.h> alias which is not implemented.

  printf
printf(3) is implemented, however floating point formatting is not currently implemented and the format specifier will instead be output verbatim. Position parameters are also not implemented yet.

  pthread_cancel
Pthread cancellation is not implemented and threads instead have to pthread_exit(3) voluntarily.

  pthread_kill
Sending a signal to a particular thread is not implemented.

  putenv
setenv(3) is the standard replacement. Note how the string provided could technically be modified at a later time.

  rand, srand
rand(3) and srand(3) are implemented, however invocations will warn that the functions are not random, and arc4random(3), arc4random_uniform(3), or arc4random_buf(3) should be used instead for random numbers.

  realpath
realpath(3) with a non-null second parameter is undefined behavior as there is no PATH_MAX limit, and should always be invoked with a null second parameter which allocates a destination buffer of the appropriate size using malloc(3).

  <resolv.h>
<resolv.h> is currently not implemented and getaddrinfo(2) can be used instead.

  sbrk
malloc(3) and mmap(2) are the standard interfaces for memory allocation.

  select
select(2) is implemented, but is defined in <sys/select.h> instead of <sys/time.h> per POSIX, however the superior poll(2) should be used instead as the fdset_t type overflows on file descriptors whose value is too large.

  sigaction SA_RESTART
Restarting system calls after signal delivery is not currently implemented and system calls instead fail with EINTR.

  socklen_t
socklen_t is typedef to size_t instead of int or unsigned int as on other operating systems.

  sprintf
sprintf(3) is implemented, however invocations will warn the function is dangerous as it does not know the size of the destination buffer and may buffer overflow if the output is unexpectedly large. snprintf(3) should be use instead as the destination buffer size should always be known, otherwise the invocation is suspicious. The superior alternative is to combine allocation and initialization using asprintf(3).

  <sys/param.h>
<sys/param.h> is not implemented as there is little agreement on what it's supposed to contain and all the contents have standard replacements or can be provided by the application itself. Inclusions are almost always unnecessary and can be removed.

  times
times(2) is implemented, however the clock_t type may overflow, and the timens(2) non-standard extension with struct timespec precision can be used instead.

  time_t
time_t is 64-bit signed and can be formatted portably cast to an intmax_t using “%ji” or with strftime(3) and such.

CLOCK_REALTIME counts the number of seconds since the epoch including leap seconds, unlike other operating systems and in violation of POSIX. CLOCK_REALTIME_HAS_LEAP_SECONDS definition advertises CLOCK_REALTIME contains leap seconds since the epoch in the TAI-10 format.

sub_leap_seconds(3) converts timestamps from TAI-10 to UTC by subtracting the leap seconds, while add_leap_seconds(3) converts timestamps from UTC TO TAI-10 by adding the leap seconds. These functions are useful when communicating with other operating systems either via the network or exchanged data files.

  u_char, u_short, u_int, u_long
unsigned char, unsigned short, unsigned int, and unsigned long are the standard types. Applications can supply the typedefs themselves if desired.

  uid_t
uid_t is 64-bit unsigned and can be formatted portably cast to a uintmax_t using “%ju”.

  u_int8_t, u_int16_t, u_int32_t, u_int64_t
uint8_t, uint16_t, uint32_t, and uint64_t are the standard types. Applications can supply the typedefs themselves if desired.

  wait3, wait4
waitpid(2) is the standard replacement.

SEE ALSO
porting(7)