UNIX standardization and Implementation Options

POSIX.1 Version 2001 includes functions specified by the iso c standard. Its interfaces are divided into two types: required interfaces and optional interfaces. The optional interfaces are further divided into 50 zones by function. Table 1 summarizes the programming interfaces that are not discarded based on their respective Option Code. The option code is an abbreviation of 2-3 characters to identify the interface that belongs to each functional area. The option code highlights the text on the relevant pages of the manual, indicating that the interface depends on the support for specific options. Many options handle real-time scaling.

Table 1 POSIX.1 optional interface groups and code (SUS, Single UNIX Specification)

Code	SUS mandatory requirements	Symbol constant	Description
ADV		_ POSIX_ADVISORY_INFO	Creation information (Real-Time)
AIO		_ POSIX_ASYNCHRONOUS_IO	Asynchronous input and output (Real-Time)
BAR		_ POSIX_BARRIERS	Barrier (Real-Time)
CPT		_ POSIX_CPUTIME	Process CPU clock (Real-Time)
CS		_ POSIX_CLOCK_SELECTION	Clock selection (Real-Time)
CX	Yes		Iso c standard extension
FSC	Yes	_ POSIX_FSYNC	File synchronization
IP6		_ POSIX_IPV6	IPv6 Interface
MF	Yes	_ POSIX_MAPPED_FILES	Store ing files
ML		_ POSIX_MEMLOCK	Process storage zone lock (Real-Time)
MLR		_ POSIX_MEMLOCK_RANGE	Lock storage area (Real-Time)
MON		_ POSIX_MONOTONIC_CLOCK	Monotonous clock (Real-Time)
Flat	Yes	_ POSIX_MEMORY_PROTECTION	Storage Protection
MSG		_ POSIX_MESSAGE_PASSING	Message transmission (Real-Time)
MX			IEC 60559 Floating Point Options
PIO		_ POSIX_PRIORITIZED_IO	Priority Input and Output
PS		_ POSIX_PRIORITIZED_SCHEDULING	Process Scheduling (Real-Time)
RS		_ POSIX_RAW_SOCKETS	Original socket
RTS		_ POSIX_REALTIME_SIGNALS	Real-time signal expansion
SEM		_ POSIX_SEMAPHORES	Semaphores (Real-Time)
SHM		_ POSIX_SHARED_MEMORY_OBJECTS	Shared storage objects (Real-Time)
SIO		_ POSIX_SYNCHRONIZED_IO	Synchronous input and output (Real-Time)
SPI		_ POSIX_SPIN_LOCKS	Spin lock (Real-Time)
SPNs		_ POSIX_SPAWN	Generation (Real-Time)
SS		_ POSIX_SPORADIC_SERVER	Server (Real-Time)
TCT		_ POSIX_THREAD_CPUTIME	Thread CPU clock (Real-Time)
TEF		_ POSIX_TRACE_EVENT_FILTER	Tracking Event Filter
THR	Yes	_ POSIX_THREADS	Thread
TMO		_ POSIX_TIMEOUTS	Timeout (Real-Time)
TMR		_ POSIX_TIMERS	Timer (Real-Time)
TPI		_ POSIX_THREAD_PRIO_INHERIT	Thread priority integration (Real-Time)
TPP		_ POSIX_THREAD_PRIO_PROTECT	Thread priority protection (Real-Time)
TPS		_ POSIX_THREAD_PRIORITY_SCHEDULING	Thread execution Scheduling (Real-Time)
TRC		_ POSIX_TRACE	Tracking
TRI		_ POSIX_TRACE_INHERIT	Tracking inheritance
TRL		_ POSIX_TRACE_LOG	Tracking log
TSA	Yes	_ POSIX_THREAD_ATTR_STACKADDR	Thread stack address attributes
TSF	Yes	_ POSIX_THREAD_SAFE_FUNCTION	Thread-safe Functions
TSH	Yes	_ POSIX_THREAD_PROCESS_SHARED	Synchronization shared by thread Processes
TSP		_ POSIX_THREAD_SPORADIC_SERVER	Thread-free server (Real-Time)
TSS	Yes	_ POSIX_THREAD_ATTR_STACKSIZE	Thread stack address size
TYM		_ POSIX_TYPED_MEMORY_OBJECTS	Typed storage objects (Real-Time)
XSI	Yes	_ XOPEN_UNIX	X/Open extension Interface
XSR		_ XOPEN_STREAMS	XSI STREAMS

Table 1 lists the POSIX.1 options. If we want to write some portable applications that are related to all the supported options, A portable method is required to determine whether an implementation supports a given option.

As with restrictions, Single UNIX Specification defines three processing methods:

(1) the options are defined in <unistd. h> during compilation.

(2) The options irrelevant to files or directories are determined using the sysconf function.

(3) options related to files or directories are discovered by calling the pathconf or fpathconf function.

The options include the symbols in the 3rd column of table 1 and the symbols in the column 2 and 3. If the symbolic constant is not defined, sysconf, pathconf, or fpathconf must be used to determine whether the option is supported. In this case, the name prefix _ POSIX of these functions must be replaced with _ SC or _ PC. For constants prefixed with _ XOPEN, _ SC or _ PC strings must be placed before the name parameter.

If the platform defines symbolic constants, there are three possibilities:

(1) If the definition value of a symbolic constant is-1, the platform does not support the corresponding options.

(2) If the definition value of a symbolic constant is greater than 0, the platform supports corresponding options.

(3) If the definition value of a symbolic constant is 0, sysconf, pathconf, or fpathconf must be called to check whether the corresponding options are supported.

Table 2 sysconf options and name Parameters

Option name	Description	Name Parameter
_ POSIX_JOB_CONTROL	Specifies whether this implementation supports job control.	_ SC _JOB_CONTROL
_ POSIX_READER_WRITER_LOCKS	Indicates whether this implementation supports reader-writer locks.	_ SC _READER_WRITER_LOCKS
_ POSIX_SAVED_IDS	Specifies whether this implementation supports saved set-uesr-ID and saved set-group-ID.	_ SC _SAVED_IDS
_ POSIX_SHELL	Whether POSIX shell is supported	_ SC _SHELL
_ POSIX_VERSION	POSIX.1 version	_ SC _VERSION
_ XOPEN_CRYPT	Indicates whether XSI encryption lists are supported.	_ SC _XOPEN_CRYPT
_ XOPEN_LEGACY	Indicates whether the implementation supports the XSI legacy region group.	_ SC _XOPEN_LEGACY
_ XOPEN_REALTIME	Whether XSI real-time quota group is supported	_ SC _XOPEN_REALTIME
_ XOPEN_REALTIME_THREADS	Indicates whether XIS Real-Time Thread groups are supported by this implementation.	_ SC _XOPEN_REALTIME_THREADS
_ XOPEN_VERSION	Specify the XSI version	_ SC _XOPEN_VERSION

Table 3 options and name parameters of pathconf and fpathconf

Option name	Description	Name Parameter
_ POSIX_CHOWN_RESTRICTED	Specifies whether chown is restricted.	_ PC_CHOWN_RESTRICTED
_ POSIX_NO_TRUNC	Indicates whether an error occurs when the path name is longer than NAME_MAX.	_ PC_NO_TRUNC
_ POSIX_VDISABLE	If defined, you can use this value to disable special characters of the terminal.	_ PC_VDISABLE
_ POSIX_ASYNC_IO	Specifies whether asynchronous I/O can be used for associated files	_ PC_ASYNC_IO
_ POSIX_PRIO_IO	Specifies whether priority I/O can be used for associated files	_ PC_PRIO_IO
_ POSIX_SYNC_IO	Specifies whether synchronization I/O can be used for associated files	_ PC_SYNC_IO

If the system limits are the same, the following points are worth noting about how to handle sysconf, pathconf, and fpathconf:

(1) the return value of _ SC _VERSION indicates the year (in 4 digits) and month (in 2 digits) related to the standard ). This value may be 198808L, 199029L, and 199506L, or other values of later versions of this version. The value related to SUS v3 is 200w.l.

(2) the return value of _ SC _XOPEN_VERSION indicates the XSI version that the system complies. The value associated with SUS v3 is 600.

(3) The values of _ SC _JOB_CONTROL, _ SC _SAVED_IDS, and _ PC_VDISABLE no longer indicate the optional functions. These functions are no longer required since SUS v3, but these symbols are retained for backward compatibility.

(4) If the specified pathname or filedes does not support this function, _ PC_CHOWN_RESTRICTED and _ PC_NO_TRUNC return-1 without changing errno.

(5) The file referenced by _ PC_CHOWN_RESTRICTED must be a file or directory. If it is a directory, the return value indicates whether the option can be applied to each file in the directory.

(6) The file referenced by _ PC_NO_TRUNC must be a directory. The return value can be used for each file name in the directory.

(7) The file referenced by _ PC_VDISABLE must be a terminal file.

To comply with SUS v3, if an option symbol is defined, its value should be set to 0,-1, or 200112. If a function is not defined, that is, the system does not define a symbolic constant or the corresponding _ SC or _ PC name, the record item is marked as "undefined ". In contrast, the "defined" record indicates that the symbolic constant has been defined, but no value is specified (for example: # define _ POSIX_THREADS ). If the system defines a symbolic constant, but its value is-1 or 0, but the corresponding sysconf or pathconf call returns-1, the record is marked as "not supported ".