spawnle()

QNX SDP8.0C Library ReferenceAPIDeveloper

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[] );

Arguments:

mode

How you want to load the child process, and how you want the parent program to behave after the child program is initiated:

P_WAIT — load the child program into available memory, execute it, and make the parent program resume execution after the child process ends.
P_NOWAIT — execute the parent program concurrently with the new child process.
P_NOWAITO — execute the parent program concurrently with the new child process. You can't use wait() to obtain the exit code.
P_OVERLAY — replace the parent program with the child program in memory and execute the child. No return is made to the parent program. This is equivalent to calling the appropriate exec*() function.

path

The full path name of the executable.

arg0, ... argn, NULL

The arguments that you want to pass to the new process. You must pass at least arg0, which by convention is a pointer to the name of the new child process, and can't be NULL. You must terminate the list with an argument of NULL.

envp

NULL, or a pointer to an array of character pointers, each pointing to a string that defines 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.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

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. This function calls spawnve().

Note:

In order to create a child process, your process must have the PROCMGR_AID_SPAWN ability enabled. For more information, see procmgr_ability().
If the new child process is a shell script, the first line must start with #!, followed by the path of the program to run to interpret the script, optionally followed by one argument. The script must also be marked as executable. For more information, see The first line in the Writing Shell Scripts chapter of the QNX OS User's Guide.

The spawnle() function is a QNX OS-specific convenience function. For greater portability and control, use posix_spawn().

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.

If envp is NULL, the child process inherits the environment of the parent process. The new process can access its environment by using the environ global variable (found in <unistd.h>).

Note:

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. For information about macros that extract information from this status, see Status macros in the documentation for wait().
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. 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.
EACCES: The calling process doesn't have permission to search a directory listed in path, or it doesn't have permission to execute path, or path's filesystem was mounted with the ST_NOEXEC flag.
EAGAIN: Insufficient resources available to create the child process.
EBADF: An error occurred duplicating open file descriptors to the new process.
ECHILD: The mode is P_WAIT, and the spawned process terminated before the call to waitpid() was completed.
EFAULT: One of the buffers specified in the function call is invalid.
EINTR: The function was interrupted by a signal.
EINVAL: An argument is invalid (e.g., arg0 is NULL, or the value of mode isn't valid).
ELOOP: Too many levels of symbolic links or prefixes.
EMFILE: Insufficient resources available to load the new executable image or to remap file descriptors in the child process.
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 underlying the path specified in path.
ENOTDIR: A component of the path prefix of the child process isn't a directory.
EPERM: The calling process doesn't have the required permission (see procmgr_ability()), or an underlying call to mmap() failed because it attempted to set PROT_EXEC for a region of memory covered by an untrusted memory-mapped file.
ETXTBSY: The text file that you're trying to execute is busy (e.g., it might be open for writing).

See also the errors for ConnectAttach() and MsgSendvnc().

Examples:

Run myprog as if the user had typed:

myprog ARG1 ARG2

on 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 OS


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

Caveats:

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

Page updated: August 09, 2024