spawnle()

Spawn a child process, given a list of arguments and an environment

Synopsis:

#include <process.h>

int spawnle( int mode, 
             const char * path, 
             const char * arg0, 
             const char * arg1..., 
             const char * argn, 
             NULL, 
             const char * envp[] );

Description:

The spawnle() function creates and executes a new child process, named in path with NULL-terminated list of arguments in arg0 ... argn and with the environment specified in envp.

The spawnle() function isn't a POSIX 1003.1 function, and isn't guaranteed to behave the same on all operating systems. It builds argv[ ] and envp[ ] arrays before calling spawn().

How the spawn functions are related

Most of the spawn*() functions do a lot of work before a message is sent to procnto.

The value of mode determines how the child process is loaded, and how the parent program behaves after the child program is initiated:

P_WAIT: The child program is loaded into available memory, is executed, dies and then the parent program resumes execution.
P_NOWAIT: Causes the parent program to execute concurrently with the new child process.
P_NOWAITO: Causes the parent program to execute concurrently with the new child process. The wait() function can't be used to obtain the exit code.
P_OVERLAY: The child program replaces the parent program in memory and is executed. No return is made to the parent program. This is equivalent to calling the appropriate exec*() function.

Arguments are passed to the child process by supplying one or more pointers to character strings as arguments. These character strings are concatenated with spaces inserted to separate the arguments to form one argument string for the child process. At least one argument, arg0, must be passed to the child process. By convention, this first argument is a pointer to the name of the new child process.

The envp argument is a pointer to an array of character pointers, each pointing to a string defining an environment variable. The array is terminated with a NULL pointer. Each pointer points to a character string of the form:

variable=value

that's used to define an environment variable. If the value of envp is NULL, then the child process inherits the environment of the parent process.

The new process can access the calling process environment by using the environ global variable (found in <unistd.h>).

A parent/child relationship doesn't imply that the child process dies when the parent process dies.

Returns:

The spawnle() function's return value depends on the mode argument:

mode	Return value
P_WAIT	The exit status of the child process.
P_NOWAIT	The process ID of the child process. To get the exit status for a P_NOWAIT process, you must use the waitpid() function, giving it this process ID.
P_NOWAITO	The process ID of the child process, or 0 if the process is being started on a remote node. You can't get the exit status of a P_NOWAITO process.

If an error occurs, -1 is returned (errno is set).

Errors:

E2BIG: The number of bytes used by the argument list or environment list of the new child process is greater than ARG_MAX bytes.
EACCESS: Search permission is denied for a directory listed in the path prefix of the new child process or the new child process's file doesn't have the execute bit set.
EAGAIN: Insufficient resources available to create the child process.
EFAULT: One of the buffers specified in the function call is invalid.
ELOOP: Too many levels of symbolic links or prefixes.
ENAMETOOLONG: The length of path exceeds PATH_MAX or a pathname component is longer than NAME_MAX.
ENOENT: The file identified by the path argument is empty, or one or more components of the pathname of the child process don't exist.
ENOEXEC: The child process's file has the correct permissions, but isn't in the correct format for an executable.
ENOMEM: Insufficient memory available to create the child process.
ENOSYS: The spawnle() function isn't implemented for the filesystem specified in path.
ENOTDIR: A component of the path prefix of the child process isn't a directory.

Examples:

Run myprog as if the user had typed:

myprog ARG1 ARG2

at the command-line:

#include <stddef.h>
#include <process.h>

char *env_list[] = { "SOURCE=MYDATA",
             "TARGET=OUTPUT",
             "lines=65",
             NULL
            };

spawnle( P_WAIT, "myprog",
    "myprog", "ARG1", "ARG2", NULL,
     env_list );

The program is found if myprog is in the current working directory. The environment for the child program consists of the three environment variables SOURCE, TARGET and lines.

Classification:

QNX 4

Safety:
Cancellation point	Read the Caveats
Interrupt handler	No
Signal handler	No
Thread	Yes

Caveats:

If mode is P_WAIT, this function is a cancellation point.