spawnp()

QNX SDP8.0C Library ReferenceAPIDeveloper

Create and execute a new child process, given a relative path

Synopsis:

#include <spawn.h>

pid_t spawnp( const char * file,
              int fd_count,
              const int fd_map[],
              const struct inheritance * inherit,
              char * const argv[],
              char * const envp[] );

Arguments:

file

If this argument contains a slash, it's used as the pathname of the executable; otherwise, the PATH environment variable is searched for file.

fd_count

The number of entries in the fd_map array. If fd_count is 0, fd_map is ignored, and the child process inherits all file descriptors (except for the ones modified with fcntl()'s FD_CLOEXEC flag).

fd_map

An array of file descriptors that you want the child process to inherit. If fd_count isn't 0, fd_map must contain at least fd_count file descriptors, up to a maximum of OPEN_MAX. The first three entries (if specified) become the child process's standard input, standard output, and standard error (stdin, stdout, and stderr).

If you set fdmap[X] to SPAWN_FDCLOSED instead of to a valid file descriptor, the file descriptor X is closed in the child process.

For more information, see Mapping file descriptors in the documentation for spawn().

inherit

A pointer to a struct inheritance that indicates what you want the child process to inherit from the parent in addition to the default attributes listed below. For more information, see inheritance structure, in the documentation for spawn(). This argument can be NULL if you want the child to inherit only the default attributes.

argv

A pointer to an argument vector. The value in argv[0] can't be NULL, and should represent the filename of the program being loaded. The last member of argv must be a NULL pointer. The value of argv can't be NULL.

envp

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.

Library:

libc

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

Description:

The spawnp() function creates and executes a new child process, named in file. It sets the SPAWN_CHECK_SCRIPT flag, and then calls spawn().

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

The child process inherits the following attributes of the parent process:

process group ID (unless SPAWN_SETGROUP is set in inherit.flags)
session membership
real user ID and real group ID
effective user ID and effective group ID
supplementary group IDs
priority and scheduling policy
current working directory and root directory
file-creation mask
signal mask (unless SPAWN_SETSIGMASK is set in inherit.flags)
signal actions specified as SIG_DFL
signal actions specified as SIG_IGN (except the ones modified by inherit.sigdefault when SPAWN_SETSIGDEF is set in inherit.flags).

The child process has several differences from the parent process:

Signals set to be caught by the parent process are set to the default action (SIG_DFL).
The child process's tms_utime, tms_stime, tms_cutime, and tms_cstime are tracked separately from the parent's.
The number of seconds left until a SIGALRM signal would be generated is set to zero for the child process.
The set of pending signals for the child process is empty.
File locks set by the parent aren't inherited.
Per-process timers created by the parent aren't inherited.
Memory locks and mappings set by the parent aren't inherited.
The child doesn't inherit the parent's default timer tolerance (set by a call to procmgr_timer_tolerance()).

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

If the file is on a filesystem mounted with the ST_NOSUID flag set, the effective user ID, effective group ID, saved set-user ID and saved set-group ID are unchanged for the child process. Otherwise, if the set-user ID mode bit is set, the effective user ID of the child process is set to the owner ID of file. Similarly, if the set-group ID mode bit is set, the effective group ID of the child process is set to the group ID of file. The real user ID, real group ID and supplementary group IDs of the child process remain the same as those of the parent process. The effective user ID and effective group ID of the child process are saved as the saved set-user ID and the saved set-group ID used by the setuid().

Suppose you call spawnp() like this:

spawnp(file, fd_count, fd_map, inherit, argv, envp);

The spawnp() function does the following:

creates an empty attribute if inherit is NULL
sets the SPAWN_CHECK_SCRIPT flag

and then calls spawn().

Note:

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

Returns:

The process ID of the child process, or -1 if an error occurs (errno is set).

Note:

If you set SPAWN_EXEC in the flags member of the inheritance structure, spawnp() doesn't return, unless an error occurred.

Errors:

E2BIG: The number of bytes used by the argument list and 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 entry in fd_map refers to an invalid file descriptor, or an error occurred duplicating open file descriptors to the new process.
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., argv[0] is NULL).
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 file exceeds PATH_MAX or a pathname component is longer than NAME_MAX.
ENOENT: The file identified by the file 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 spawnp() function isn't implemented for the filesystem underlying the path specified in file.
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().

Classification:

QNX OS


Safety:
Cancellation point	No
Signal handler	No
Thread	Yes

Page updated: August 09, 2024