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Standards, Environments, and Macros attributes(5)

NAME

attributes, architecture, availability, CSI, stability, MT-

Level, standard - attributes of interfaces

DESCRIPTION

The ATTRIBUTES section of a manual page contains a table

defining attribute types and their corresponding values. The following is an example of an attributes table. Not all attribute types are appropriate for all types of interfaces.

____________________________________________________________

| ATTRIBUTE TYPE | ATTRIBUTE VALUE |

|_____________________________|_____________________________|

| Architecture | SPARC |

|_____________________________|_____________________________|

| Availability | system/kernel |

|_____________________________|_____________________________|

| CSI | Enabled |

|_____________________________|_____________________________|

| Interface Stability | Committed |

|_____________________________|_____________________________|

| MT-Level | Safe |

|_____________________________|_____________________________|

| Standard | See standards(5). |

|_____________________________|_____________________________|

Architecture

Architecture defines processor or specific hardware. See -p

option of uname(1). In some cases, it may indicate required adapters or peripherals. Availability

This refers to the software package which contains the com-

mand or component being described on the man page. To be able to use the command, the indicated package must have been installed. For information on how to add a package see pkgadd(1M). Code Set Independence (CSI)

OS utilities and libraries free of dependencies on the pro-

perties of any code sets are said to have Code Set Indepen-

dence (CSI). They have the attribute of being CSI enabled. This is in contrast to many commands and utilities, for example, that work only with Extended Unix Codesets (EUC), an encoding method that allows concurrent support for up to four code sets and is commonly used to represent Asian character sets.

SunOS 5.11 Last change: 29 Jul 2007 1

Standards, Environments, and Macros attributes(5) For practical reasons, however, this independence is not absolute. Certain assumptions are still applied to the current CSI implementation: o File code is a superset of ASCII.

o To support multi-byte characters and null-

terminated UNIX file names, the NULL and / (slash)

characters cannot be part of any multi-byte charac-

ters. o Only "stateless" file code encodings are supported. Stateless encoding avoids shift, locking shift, designation, invocation, and so forth, although single shift is not excluded.

o Process code (wchar_t values) is implementation

dependent and can change over time or between implementations or between locales.

o Not every object can have names composed of arbi-

trary characters. The names of the following objects must be composed of ASCII characters: o User names, group name, and passwords o System name o Names of printers and special devices o Names of terminals (/dev/tty*) o Process ID numbers o Message queues, semaphores, and shared memory labels.

o The following may be composed of ISO Latin-1 or

EUC characters: o File names o Directory names o Command names o Shell variables and environmental variable names o Mount points for file systems o NIS key names and domain names

SunOS 5.11 Last change: 29 Jul 2007 2

Standards, Environments, and Macros attributes(5) o The names of NFS shared files should be composed of ASCII characters. Although files and directories may have names and contents composed of characters

from non-ASCII code sets, using only the ASCII

codeset allows NFS mounting across any machine, regardless of localization. For the commands and utilities that are CSI enabled, all can handle

single-byte and multi-byte locales released in 2.6.

For applications to get full support of interna-

tionalization services, dynamic binding has to be applied. Statically bound programs will only get support for C and POSIX locales. Interface Stability

Sun often provides developers with early access to new tech-

nologies, which allows developers to evaluate with them as soon as possible. Unfortunately, new technologies are prone

to changes and standardization often results in interface

incompatibility from previous versions. To make reasonable risk assessments, developers need to know how likely an interface is to change in future releases. To

aid developers in making these assessments, interface sta-

bility information is included on some manual pages for

commands, entry-points, and file formats.

The more stable interfaces can safely be used by nearly all applications, because Sun will endeavor to ensure that these continue to work in future minor releases. Applications that depend only on Committed interfaces should reliably continue to function correctly on future minor releases (but not necessarily on earlier major releases).

The less stable interfaces allow experimentation and proto-

typing, but should be used only with the understanding that they might change incompatibly or even be dropped or replaced with alternatives in future minor releases. "Interfaces" that Sun does not document (for example, most kernel data structures and some symbols in system header

files) may be implementation artifacts. Such internal inter-

faces are not only subject to incompatible change or remo-

val, but we are unlikely to mention such a change in release notes. Release Levels Products are given release levels, as well as names, to aid compatibility discussions. Each release level may also

SunOS 5.11 Last change: 29 Jul 2007 3

Standards, Environments, and Macros attributes(5) include changes suitable for lower levels. Release Version Significance

_____________________________________________________________

Major x.0 Likely to contain major feature additions; adhere to different,

possibly incompatible standard

revisions; and though unlikely, could change, drop, or replace Committed interfaces. Initial product releases are usually 1.0.

_____________________________________________________________

Minor x.y Compared to an x.0 or earlier release (y!=0), it is likely to

contain: feature additions, com-

patible changes to Committed

interfaces, or likely incompati-

ble changes to Uncommitted or Volatile interfaces.

_____________________________________________________________

Micro x.y.z Intended to be interface compati-

ble with the previous release (z!=0), but likely to add bug fixes, performance enhancements, and support for additional hardware. Incompatible changes to Volatile interfaces are possible. In the context of interface stability, update releases

(occasionally referred to as patch releases) should be con-

sidered equivalent to Micro Releases. Classifications

The following table summarizes how stability level classif-

ications relate to release level. The first column lists the Stability Level. The second column lists the Release Level for Incompatible Changes, and the third column lists other

comments. For a complete discussion of individual classifi-

cations, see the appropriate subsection below. Stability Release Comments

________________________________________________________________

Committed Major (x.0) Incompatibilities are exceptional.

________________________________________________________________

Uncommitted Minor (x.y) Incompatibilities are common.

________________________________________________________________

SunOS 5.11 Last change: 29 Jul 2007 4

Standards, Environments, and Macros attributes(5) Volatile Micro (x.y.z) Incompatibilities are common. The interface stability level classifications described on this manual page apply to both source and binary interfaces unless otherwise stated. All stability level classifications

are public, with the exception of the Private classifica-

tion. The precise stability level of a public interface (one that is documented in the manual pages) is unspecified

unless explicitly stated. The stability level of an undocu-

mented interface is implicitly Private. The existence of documentation other than the documentation that is a component of the Solaris product should not be construed to imply any level of stability for interfaces

provided by the Solaris product. The only source of stabil-

ity level information is Solaris manual pages. Committed The intention of a Committed interface is to enable

third parties to develop applications to these inter-

faces, release them, and have confidence that they will run on all releases of the product after the one in which the interface was introduced, and within the same Major release. Even at a Major release, incompatible

changes are expected to be rare, and to have strong jus-

tifications.

Interfaces defined and controlled as industry standards

are most often treated as Committed interfaces. In this case, the controlling body and/or public, versioned document is typically noted in a "Standard" entry in the Attributes table or elsewhere in the documentation. Although a truly exceptional event, incompatible changes are possible in any release if the associated defect is serious enough as outlined in the Exceptions section of this document or in a Minor release by following the End of Feature process. If support of a Committed interface

must be discontinued, Sun will attempt to provide notif-

ication and the stability level will be marked Obsolete. Uncommitted

No commitment is made about either source or binary com-

patibility of these interfaces from one Minor release to

the next. Even the drastic incompatible change of remo-

val of the interface in a Minor release is possible.

SunOS 5.11 Last change: 29 Jul 2007 5

Standards, Environments, and Macros attributes(5) Uncommitted interfaces are generally not appropriate for

use by release-independent products.

Incompatible changes to the interface are intended to be motivated by true improvement to the interface which may

include ease of use considerations. The general expec-

tation should be that Uncommitted interfaces are not likely to change incompatibly and if such changes occur

they will be small in impact and may often have a miti-

gation plan. Uncommitted interfaces generally fall into one of the following subcategorizes:

1. Interfaces that are experimental or transi-

tional. They are typically used to give outside developers early access to new or rapidly changing technology, or to provide an interim solution to a problem where a more general solution is anticipated. 2. Interfaces whose specification is controlled by

an outside body yet Sun expects to make a rea-

sonable effort to maintain compatibility with previous releases until the next Minor release at which time Sun expects to synchronize with the external specification.

3. Interfaces whose target audience values innova-

tion (and possibly ease of use) over stability.

This attribute is often associated with admin-

istrative interfaces for higher tier com-

ponents. For Uncommitted interfaces, Sun makes no claims about either source or binary compatibility from one minor release to another. Applications developed based on these interfaces may not work in future minor releases. Volatile Volatile interfaces can change at any time and for any reason.

The Volatile interface stability level allows Sun pro-

ducts to quickly track a fluid, rapidly evolving specif-

ication. In many cases, this is preferred to providing additional stability to the interface, as it may better meet the expectations of the consumer. The most common application of this taxonomy level is to interfaces that are controlled by a body other than Sun,

SunOS 5.11 Last change: 29 Jul 2007 6

Standards, Environments, and Macros attributes(5)

but unlike specifications controlled by standards bodies

or Free or Open Source Software (FOSS) communities which value interface compatibility, it can not be asserted

that an incompatible change to the interface specifica-

tion would be exceedingly rare. It may also be applied to FOSS controlled software where it is deemed more important to track the community with minimal latency than to provide stability to our customers. It also common to apply the Volatile classification level to interfaces in the process of being defined by trusted or widely accepted organization. These are

generically referred to as draft standards. An "IETF

Internet draft" is a well understood example of a specification under development. Volatile can also be applied to experimental interfaces. No assertion is made regarding either source or binary compatibility of Volatile interfaces between any two releases, including patches. Applications containing these interfaces might fail to function properly in any future release.

Not-an-Interface

The situation occasionally occurs where there exists an entity that could be inferred to be an interface, but actually is not. Common examples are output from CLIs intended only for human consumption and the exact layout of a GUI. This classification is a convenience term to be used to

clarify such situations where such confusion is identi-

fied as likely. Failure to apply this term to an entity is not an indication that the entity is some form of interface. It only indicates that the potential for confusion was not identified. Private

A Private interface is an interface provided by a com-

ponent (or product) intended only for the use of that component. A Private interface might still be visible to or accessible by other components. Because the use of interfaces private to another component carries great stability risks, such use is explicitly not supported. Components not supplied by Sun Microsystems should not use Private interfaces.

SunOS 5.11 Last change: 29 Jul 2007 7

Standards, Environments, and Macros attributes(5) Most Private interfaces are not documented. It is an exceptional case when a Private interface is documented. Reasons for documenting a Private interface include, but are not limited to, the intention that the interface might be reclassified to one of the public stability level classifications in the future or the fact that the interface is inordinately visible. Obsolete Obsolete is a modifier that can appear in conjunction with the above classification levels. The Obsolete modifier indicates an interface that is "deprecated" and/or no longer advised for general use. An existing interface may be downgraded from some other status (such as Committed or Uncommitted) by the application of the Obsolete modifier to encourage customers to migrate from that interface before it may be removed (or incompatibly changed). An Obsolete interface is supported in the current release, but is scheduled to be removed in a future (minor) release. When support of an interface is to be discontinued, Sun will attempt to provide notification

before discontinuing support. Use of an Obsolete inter-

face may produce warning messages. Exceptions There are rare instances when it is in the best interest of both Sun and the customer to break the interface stability commitment. The following list contains the common, known reasons for the interface provider to violate an interface stability commitment, but does not preclude others. 1. Security holes where the vulnerability is inherent in the interface. 2. Data corruption where the vulnerability is inherent in the interface. 3. Standards violations uncovered by a change in interpretation or enhancement of conformance tests. 4. An interface specification which isn't controlled by Sun has been changed incompatibly and the vast majority of interface consumers expect the newer interface. 5. Not making the incompatible change would be incomprehensible to our customers. One example of

SunOS 5.11 Last change: 29 Jul 2007 8

Standards, Environments, and Macros attributes(5) this would to have not incompatibly changed pcfs

when the DOS 8.3 naming restrictions were aban-

doned. Incompatible changes allowed by exception will always be delivered in the "most major" release vehicle possible. However, often the consequences of the vulnerabilities or contractual branding requirements will force delivery in a patch. Compatibility with Earlier Interface Classification Schemes In releases up to and including Solaris 10, a different interface classification scheme was used. The following

table summarizes the mapping between the old and new clas-

sification schemes. Old New Comments

_________________________________________________________________

Standard Committed An entry in the attributes table for the Standard attribute type should appear. Stable Committed Name change. Evolving Uncommitted Actual commitments match. Unstable Uncommitted Name change. External Volatile Name change with expansion of allowed usage. Obsolete (Obsolete) Was a classification, now a modifier. The increased importance of Free or Open Source Software

motivated the name change from Stable/Unstable to

Committed/Uncommitted. Stable conflicted with the common use of the term in FOSS communities.

Ambiguity in the definition of Evolving was causing diffi-

culty in interpretation. As part of the migration to the new classification scheme, many formerly Evolving interfaces were upgraded to Committed. However, upon encountering the term Evolving, Uncommitted should be inferred.

MT-Level

Libraries are classified into categories that define their ability to support multiple threads. Manual pages containing functions that are of multiple or differing levels describe

this in their NOTES or USAGE section.

SunOS 5.11 Last change: 29 Jul 2007 9

Standards, Environments, and Macros attributes(5) Safe Safe is an attribute of code that can be called from a multithreaded application. The effect of calling into a Safe interface or a safe code segment is that the results are valid even when called by multiple threads. Often overlooked is the fact that the result of this Safe interface or safe code segment can have global consequences that affect all threads. For example, the action of opening or closing a file from one thread is

visible by all the threads within a process. A mul-

tithreaded application has the responsibility for using these interfaces in a safe manner, which is different from whether or not the interface is Safe. For example, a multithreaded application that closes a file that is still in use by other threads within the application is not using the close(2) interface safely. Unsafe An Unsafe library contains global and static data that is not protected. It is not safe to use unless the

application arranges for only one thread at time to exe-

cute within the library. Unsafe libraries might contain functions that are Safe; however, most of the library's functions are unsafe to call. Some functions that are

Unsafe have reentrant counterparts that are MT-Safe.

Reentrant functions are designated by the _r suffix

appended to the function name.

MT-Safe

An MT-Safe library is fully prepared for multithreaded

access. It protects its global and static data with

locks, and can provide a reasonable amount of con-

currency. A library can be safe to use, but not MT-Safe.

For example, surrounding an entire library with a moni-

tor makes the library Safe, but it supports no con-

currency so it is not considered MT-Safe. An MT-Safe

library must permit a reasonable amount of concurrency. (This definition's purpose is to give precision to what

is meant when a library is described as Safe. The defin-

ition of a Safe library does not specify if the library

supports concurrency. The MT-Safe definition makes it

clear that the library is Safe, and supports some con-

currency. This clarifies the Safe definition, which can mean anything from being single threaded to being any degree of multithreaded.)

SunOS 5.11 Last change: 29 Jul 2007 10

Standards, Environments, and Macros attributes(5)

Async-Signal-Safe

Async-Signal-Safe refers to particular library functions

that can be safely called from a signal handler. A

thread that is executing an Async-Signal-Safe function

will not deadlock with itself if interrupted by a sig-

nal. Signals are only a problem for MT-Safe functions

that acquire locks.

Async-Signal-Safe functions are also MT-Safe. Signals

are disabled when locks are acquired in Async-Signal-

Safe functions. These signals prevent a signal handler that might acquire the same lock from being called.

MT-Safe with Exceptions

See the NOTES or USAGE sections of these pages for a

description of the exceptions. Safe with Exceptions

See the NOTES or USAGE sections of these pages for a

description of the exceptions.

Fork-Safe

The fork(2) function replicates only the calling thread in the child process. The fork1(2) function exists for compatibility with the past and is synonymous with fork(). If a thread other than the one performing the fork holds a lock when fork() is called, the lock will still be held in the child process but there will be no lock owner since the owning thread was not replicated. A child calling a function that attempts to acquire the lock will deadlock itself.

When fork() is called, a Fork-Safe library arranges to

have all of its internal locks held only by the thread performing the fork. This is usually accomplished with

pthread_atfork(3C), which is called when the library is

initialized. The forkall(2) function provides the capability for the rare case when a process needs to replicate all of its

threads when performing a fork. No pthread_atfork()

actions are performed when forkall() is called. There are dangers associated with calling forkall(). If some

threads in a process are performing I/O operations when another thread calls forkall(), they will continue

SunOS 5.11 Last change: 29 Jul 2007 11

Standards, Environments, and Macros attributes(5)

performing the same I/O operations in both the parent and child processes, possibly causing data corruption.

For this and other race-condition reasons, the use of

forkall() is discouraged. In all Solaris releases prior to Solaris 10, the

behavior of fork() depended on whether or not the appli-

cation was linked with -lpthread (POSIX threads, see

standards(5)). If linked with -lpthread, fork() behaved

like fork1(); otherwise it behaved like forkall(). To avoid any confusion concerning the behavior of fork(), applications can specifically call fork1() or forkall() as appropriate.

Cancel-Safety

If a multithreaded application uses pthread_cancel(3C)

to cancel (that is, kill) a thread, it is possible that the target thread is killed while holding a resource, such as a lock or allocated memory. If the thread has not installed the appropriate cancellation cleanup handlers to release the resources appropriately (see

pthread_cancel(3C)), the application is "cancel-unsafe",

that is, it is not safe with respect to cancellation. This unsafety could result in deadlocks due to locks not released by a thread that gets cancelled, or resource leaks; for example, memory not being freed on thread cancellation. All applications that use

pthread_cancel(3C) should ensure that they operate in a

Cancel-Safe environment. Libraries that have cancella-

tion points and which acquire resources such as locks or allocate memory dynamically, also contribute to the

cancel-unsafety of applications that are linked with

these libraries. This introduces another level of safety

for libraries in a multithreaded program: Cancel-Safety.

There are two sub-categories of Cancel-Safety:

Deferred-Cancel-Safety, and Asynchronous-Cancel-Safety.

An application is considered to be Deferred-Cancel-Safe

when it is Cancel-Safe for threads whose cancellation

type is PTHREAD_CANCEL_DEFERRED. An application is con-

sidered to be Asynchronous-Cancel-Safe when it is

Cancel-Safe for threads whose cancellation type is

PTHREAD_CANCEL_ASYNCHRONOUS. Deferred-Cancel-Safety is

easier to achieve than Asynchronous-Cancel-Safety, since

a thread with the deferred cancellation type can be can-

celled only at well-defined cancellation points, whereas

a thread with the asynchronous cancellation type can be cancelled anywhere. Since all threads are created by default to have the deferred cancellation type, it might never be necessary to worry about asynchronous cancel safety. Most applications and libraries are expected to

SunOS 5.11 Last change: 29 Jul 2007 12

Standards, Environments, and Macros attributes(5)

always be Asynchronous-Cancel-Unsafe. An application

which is Asynchronous-Cancel-Safe is also, by defini-

tion, Deferred-Cancel-Safe.

Standard

Many interfaces are defined and controlled as industry stan-

dards. When this is the case, the controlling body and/or public, versioned document is noted in this section. Programmers producing portable applications should rely on

the interface descriptions present in the standard or

specification to which the application is intended to con-

form, rather than the manual page descriptions of interfaces

based upon a public standard. When the standard or specifi-

cation allows alternative implementation choices, the manual page usually only describes the alternative implemented by

Sun. The manual page also describes any compatible exten-

sions to the base definition of Standard interfaces provided by Sun.

No endorsement of the referenced controlling body or docu-

ment should be inferred by its presence as a "Standard"

entry. The controlling body may be a very formal organiza-

tion, as in ISO or ANSII, a less formal, but generally accepted organization such as IETF, or as informal as the sole contributor in the case of FOSS (Free or Open Source Software).

uname(1), pkgadd(1M), Intro(3), standards(5)

SunOS 5.11 Last change: 29 Jul 2007 13

Manual Pages for UNIX Operating System command usage for man standard

NAME

Level, standard - attributes of interfaces

DESCRIPTION

The ATTRIBUTES section of a manual page contains a table

| ATTRIBUTE TYPE | ATTRIBUTE VALUE |

| Standard | See standards(5). |

to changes and standardization often results in interface

possibly incompatible standard

Interfaces defined and controlled as industry standards

but unlike specifications controlled by standards bodies

generically referred to as draft standards. An "IETF

this in their NOTES or USAGE section.

See the NOTES or USAGE sections of these pages for a

See the NOTES or USAGE sections of these pages for a

standards(5)). If linked with -lpthread, fork() behaved

the interface descriptions present in the standard or

based upon a public standard. When the standard or specifi-

SEE ALSO

uname(1), pkgadd(1M), Intro(3), standards(5)