The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### NAME

> posix_spawn_file_actions_adddup2 - add dup2 action to spawn file actions object (ADVANCED REALTIME)

#### SYNOPSIS

> ``[SPN] #include <spawn.h>
> int posix_spawn_file_actions_adddup2(posix_spawn_file_actions_t
> *`file_actions`, int` fildes`, int` newfildes`);``
> `
> `

#### DESCRIPTION

> The posix_spawn_file_actions_adddup2() function shall add a dup2() action to the object referenced by file_actions that shall cause the file descriptor fildes to be duplicated as newfildes (as if dup2(fildes, newfildes) had been called) when a new process is spawned using this file actions object.

> A spawn file actions object is as defined in posix_spawn_file_actions_addclose.

#### RETURN VALUE

> Upon successful completion, the posix_spawn_file_actions_adddup2() function shall return zero; otherwise, an error number shall be returned to indicate the error.

#### ERRORS

> The posix_spawn_file_actions_adddup2() function shall fail if:

> [EBADF]
>   The value specified by fildes or newfildes is negative or greater than or equal to {OPEN_MAX}.
> [ENOMEM]
>   Insufficient memory exists to add to the spawn file actions object.

> The posix_spawn_file_actions_adddup2() function may fail if:

> [EINVAL]
>   The value specified by file_actions is invalid.

> It shall not be considered an error for the fildes argument passed to the posix_spawn_file_actions_adddup2() function to specify a file descriptor for which the specified operation could not be performed at the time of the call. Any such error will be detected when the associated file actions object is later used during a posix_spawn() or posix_spawnp() operation.

The following sections are informative.

#### EXAMPLES

> None.

#### APPLICATION USAGE

> The posix_spawn_file_actions_adddup2() function is part of the Spawn option and need not be provided on all implementations.

> Implementations may use file descriptors that must be inherited into child processes for the child process to remain conforming, such as for message catalog or tracing purposes. Therefore, an application that calls posix_spawn_file_actions_adddup2() with an arbitrary integer for newfildes risks non-conforming behavior, and this function can only portably be used to overwrite file descriptor values that the application has obtained through explicit actions, or for the three file descriptors corresponding to the standard file streams. In order to avoid a race condition of leaking an unintended file descriptor into a child process, an application should consider opening all file descriptors with the FD_CLOEXEC bit set unless the file descriptor is intended to be inherited across exec.

#### RATIONALE

> Refer to the RATIONALE section in posix_spawn_file_actions_addclose.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> dup, posix_spawn, posix_spawn_file_actions_addclose, posix_spawn_file_actions_destroy

> XBD <spawn.h>

#### CHANGE HISTORY

> First released in Issue 6. Derived from IEEE Std 1003.1d-1999.

> IEEE PASC Interpretation 1003.1 #104 is applied, noting that the [EBADF] error can apply to the newfildes argument in addition to fildes.

#### Issue 7

> POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0440 [149] is applied.

End of informative text.

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