There has been a recent (very recent, like within the past few hours) proposal
to add the ability to do a chdir() (or fchdir()) to posix_spawn
There are more changes than what are included here, but the rest are mostly
all just boilerplate changes to support this addition.
If anyone has any comments, I'm happy to pass them along, or you can directly
(this is issue 1208 if anyone wants to comment directly.)
kre
[I have made some whitespace and line wrapping changes to this text]
posix_spawn_file_actions_addchdir( )
NAME
posix_spawn_file_actions_addchdir, posix_spawn_file_actions_addfchdir - add
chdir or fchdir action to spawn file actions object (ADVANCED REALTIME)
SYNOPSIS
#include <spawn.h>
int posix_spawn_file_actions_addchdir(posix_spawn_file_actions_t *restrict
file_actions,
const char *restrict path);
int posix_spawn_file_actions_addfchdir(posix_spawn_file_actions_t
*file_actions,
int filedes);
DESCRIPTION
The posix_spawn_file_actions_addchdir( ) function shall add a chdir action
to the
object referenced by file_actions that shall cause the working directory to
be set to
path (as if chdir(path) had been called) when a new process is spawned
using this
file actions object. A relative path shall be interpreted in relation to
the working
directory determined by any prior actions. The string described by path
shall be
copied by the posix_spawn_file_actions_addchdir( ) function.
The posix_spawn_file_actions_addfchdir( ) function shall add a fchdir
action to the
object referenced by file_actions that shall cause the working directory to
be set to
filedes (as if fchdir(filedes) 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( ).
File actions are performed in a new process created by posix_spawn( ) or
posix_spawnp( ) in the same order that they were added to the file actions
object.
Thus, the execution of an addopen action that was created by a call to
posix_spawn_file_actions_addopen( ) that specifies a relative path will be
affected
by the execution of a chdir or fchdir action that was created by a previous
call to
posix_spawn_file_actions_addchdir( ) or posix_spawn_file_actions_addfchdir(
).
Likewise, a relative path passed to posix_spawn( ) will be affected by the
last chdir
or fchdir action in the file action list.
RETURN VALUE
Upon successful completion, these functions shall return zero; otherwise,
an error
number shall be returned to indicate the error.
ERRORS
The posix_spawn_file_actions_addfchdir( ) function shall fail if:
[EBADF] The value specified by fildes is negative.
These functions shall fail if:
[ENOMEM] Insufficient memory exists to add to the spawn file actions object.
It shall not be considered an error for the path or fildes argument passed
to these
functions to specify a path or 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.
These functions may fail if:
[EINVAL] The value specified by file_actions is invalid.
EXAMPLES
None.
APPLICATION USAGE
The posix_spawn_file_actions_addchdir( ) and
posix_spawn_file_actions_addfchdir( )
functions are part of the Spawn option and need not be provided on all
implementations.
Changing the working directory of a child process can be useful when
invoking
utilities such as pax. Furthermore, the ability to add fchdir actions to
posix_spawn( )
gives the caller as much control over relative pathnames processed in the
context
of the child as it would otherwise have using openat( ), since all file
actions are
processed in sequence in the context of the child at a point where the
child process
is still single-threaded. Without chdir or fchdir actions, changing the
working
directory of the child would require a shim utility (some implementations
provide
env -C /new/path program args...
as an extension, but the standard does not require this extension), or else
temporarily
changing the working directory in the parent process prior to calling
posix_spawn( )
(but this requires locking in a multi-threaded process, to ensure that no
other thread
is impacted by the temporary change to global state).
RATIONALE
Refer to the RATIONALE section in posix_spawn_file_actions_addclose( ).
FUTURE DIRECTIONS
None.
SEE ALSO
chdir( ), fchdir( ), posix_spawn( ), posix_spawn_file_actions_addclose( ),
posix_spawn_file_actions_destroy( ).
XBD <spawn.h>
CHANGE HISTORY
First released in Issue 8. Derived from Solaris
posix_spawn_file_actions_addchdir_np.
