spawnp()

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.

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 OPEN_MAX FDs. The first three entries (if specified) become the child process's standard input, standard output, and standard error (stdin, stdout, and stderr). If fd_count is 0, fd_map is ignored.

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.

If fd_count is 0, the child process inherits all file descriptors (except for the ones modified with fcntl()'s FD_CLOEXEC flag).

inherit

A structure, of type struct inheritance, that indicates what you want the child process to inherit from the parent. For more information, see “inheritance structure,” in the documentation for spawn().

---

If you want to spawnp() remotely, set the nd member of the inheritance structure to the node descriptor. See the netmgr_strtond() function.

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argv

A pointer to an argument vector. The value in argv[0] should represent the filename of the program being loaded, but can be NULL if no arguments are being passed. 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 and SPAWN_SEARCH_PATH flags, and then calls spawn().

---

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 Neutrino User's Guide.

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The spawnp() function is a QNX function (based on the POSIX 1003.1d draft standard). The C library also includes several specialized spawn*() functions. Their names consist of spawn followed by several letters:

To view the documentation for a function, click its name in this diagram:

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

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.

If the child process is spawned on a remote node, the process group ID and the session membership aren't set; the child process is put into a new session and a new process group.

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 CHECK_SCRIPT flag
• sets the SPAWN_SEARCH_PATH flag

and then calls spawn().

---

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

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Returns:

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

---

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

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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.

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 or file'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.

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 specified in file.

ENOTDIR

A component of the path prefix of the child process isn't a directory.

Classification:

QNX Neutrino

See also:

execl(), execle(), execlp(), execlpe(), execv(), execve(), execvp(), execvpe(), getenv(), netmgr_strtond(), putenv(), setenv(), sigaddset(), sigdelset(), sigemptyset(), sigfillset(), spawn(), spawnl(), spawnle(), spawnlp(), spawnlpe(), spawnv(), spawnve(), spawnvp(), spawnvpe(), wait(), waitpid()

Processes and Threads chapter of Getting Started with QNX Neutrino