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FPATHCONF(P)			    POSIX Programmer's Manual			     FPATHCONF(P)

NAME
       fpathconf, pathconf - get configurable pathname variables

SYNOPSIS
       #include <unistd.h>

       long fpathconf(int fildes, int name);
       long pathconf(const char *path, int name);

DESCRIPTION
       The  fpathconf()  and  pathconf() functions shall determine the current value of a config-
       urable limit or option (variable) that is associated with a file or directory.

       For pathconf(), the path argument points to the pathname of a file or directory.

       For fpathconf(), the fildes argument is an open file descriptor.

       The name argument represents the variable to be queried relative to that  file  or  direc-
       tory. Implementations shall support all of the variables listed in the following table and
       may support others.  The  variables  in	the  following	table  come  from  <limits.h>  or
       <unistd.h> and the symbolic constants, defined in <unistd.h>, are the corresponding values
       used for name.

		    Variable			Value of name		Requirements
		    {FILESIZEBITS}		_PC_FILESIZEBITS	3,4
		    {LINK_MAX}			_PC_LINK_MAX		1
		    {MAX_CANON} 		_PC_MAX_CANON		2
		    {MAX_INPUT} 		_PC_MAX_INPUT		2
		    {NAME_MAX}			_PC_NAME_MAX		3,4
		    {PATH_MAX}			_PC_PATH_MAX		4,5
		    {PIPE_BUF}			_PC_PIPE_BUF		6
		    {POSIX_ALLOC_SIZE_MIN}	_PC_ALLOC_SIZE_MIN
		    {POSIX_REC_INCR_XFER_SIZE}	_PC_REC_INCR_XFER_SIZE
		    {POSIX_REC_MAX_XFER_SIZE}	_PC_REC_MAX_XFER_SIZE
		    {POSIX_REC_MIN_XFER_SIZE}	_PC_REC_MIN_XFER_SIZE
		    {POSIX_REC_XFER_ALIGN}	_PC_REC_XFER_ALIGN
		    {SYMLINK_MAX}		_PC_SYMLINK_MAX 	4,9
		    _POSIX_CHOWN_RESTRICTED	_PC_CHOWN_RESTRICTED	7
		    _POSIX_NO_TRUNC		_PC_NO_TRUNC		3,4
		    _POSIX_VDISABLE		_PC_VDISABLE		2
		    _POSIX_ASYNC_IO		_PC_ASYNC_IO		8
		    _POSIX_PRIO_IO		_PC_PRIO_IO		8
		    _POSIX_SYNC_IO		_PC_SYNC_IO		8

   Requirements
	1. If path or fildes refers to a directory, the value returned shall apply to the  direc-
	   tory itself.

	2. If  path  or  fildes  does  not refer to a terminal file, it is unspecified whether an
	   implementation supports an association of the variable name with the specified file.

	3. If path or fildes refers to a directory, the value returned shall apply  to	filenames
	   within the directory.

	4. If  path  or fildes does not refer to a directory, it is unspecified whether an imple-
	   mentation supports an association of the variable name with the specified file.

	5. If path or fildes refers to a directory, the  value	returned  shall  be  the  maximum
	   length of a relative pathname when the specified directory is the working directory.

	6. If path refers to a FIFO, or fildes refers to a pipe or FIFO, the value returned shall
	   apply to the referenced object. If path or fildes refers to	a  directory,  the  value
	   returned  shall  apply to any FIFO that exists or can be created within the directory.
	   If path or fildes refers to any other type of  file,  it  is  unspecified  whether  an
	   implementation supports an association of the variable name with the specified file.

	7. If  path or fildes refers to a directory, the value returned shall apply to any files,
	   other than directories, that exist or can be created within the directory.

	8. If path or fildes refers to a directory, it is unspecified whether  an  implementation
	   supports an association of the variable name with the specified file.

	9. If  path  or  fildes  refers  to  a directory, the value returned shall be the maximum
	   length of the string that a symbolic link in that directory can contain.

RETURN VALUE
       If name is an invalid value, both pathconf() and fpathconf() shall return -1 and set errno
       to indicate the error.

       If  the	variable corresponding to name has no limit for the path or file descriptor, both
       pathconf() and fpathconf() shall return -1 without changing errno. If  the  implementation
       needs  to  use path to determine the value of name and the implementation does not support
       the association of name with the file specified by path, or if the process  did	not  have
       appropriate  privileges to query the file specified by path, or path does not exist, path-
       conf() shall return -1 and set errno to indicate the error.

       If the implementation needs to use fildes to determine the value of name and the implemen-
       tation  does  not support the association of name with the file specified by fildes, or if
       fildes is an invalid file descriptor, fpathconf() shall return -1 and set errno	to  indi-
       cate the error.

       Otherwise,  pathconf() or fpathconf() shall return the current variable value for the file
       or directory without changing errno. The value returned shall not be more restrictive than
       the  corresponding value available to the application when it was compiled with the imple-
       mentation's <limits.h> or <unistd.h>.

ERRORS
       The pathconf() function shall fail if:

       EINVAL The value of name is not valid.

       ELOOP  A loop exists in symbolic links encountered during resolution of the path argument.

       The pathconf() function may fail if:

       EACCES Search permission is denied for a component of the path prefix.

       EINVAL The implementation does not support an association of the variable  name	with  the
	      specified file.

       ELOOP  More  than  {SYMLOOP_MAX}  symbolic links were encountered during resolution of the
	      path argument.

       ENAMETOOLONG
	      The length of the path argument exceeds  {PATH_MAX}  or  a  pathname  component  is
	      longer than {NAME_MAX}.

       ENAMETOOLONG
	      As a result of encountering a symbolic link in resolution of the path argument, the
	      length of the substituted pathname string exceeded {PATH_MAX}.

       ENOENT A component of path does not name an existing file or path is an empty string.

       ENOTDIR
	      A component of the path prefix is not a directory.

       The fpathconf() function shall fail if:

       EINVAL The value of name is not valid.

       The fpathconf() function may fail if:

       EBADF  The fildes argument is not a valid file descriptor.

       EINVAL The implementation does not support an association of the variable  name	with  the
	      specified file.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       The  pathconf() function was proposed immediately after the sysconf() function when it was
       realized that some configurable values may differ across file system, directory, or device
       boundaries.

       For  example,  {NAME_MAX}  frequently changes between System V and BSD-based file systems;
       System V uses a maximum of 14, BSD 255.	On an implementation that provides both types  of
       file systems, an application would be forced to limit all pathname components to 14 bytes,
       as this would be the value specified in <limits.h> on such a system.

       Therefore, various useful values can be queried on any pathname or file descriptor, assum-
       ing that the appropriate permissions are in place.

       The  value  returned  for  the variable {PATH_MAX} indicates the longest relative pathname
       that could be given if the specified directory is the process' current working  directory.
       A process may not always be able to generate a name that long and use it if a subdirectory
       in the pathname crosses into a more restrictive file system.

       The value returned for the variable _POSIX_CHOWN_RESTRICTED also  applies  to  directories
       that  do not have file systems mounted on them. The value may change when crossing a mount
       point, so applications that need to know should check for each directory. (An even  easier
       check is to try the chown() function and look for an error in case it happens.)

       Unlike  the  values returned by sysconf(), the pathname-oriented variables are potentially
       more volatile and are not guaranteed to remain constant throughout the process'	lifetime.
       For example, in between two calls to pathconf(), the file system in question may have been
       unmounted and remounted with different characteristics.

       Also note that most of the errors are optional. If one of the  variables  always  has  the
       same  value  on	an  implementation, the implementation need not look at path or fildes to
       return that value and is, therefore, not required to detect any of the errors  except  the
       meaning of [EINVAL] that indicates that the value of name is not valid for that variable.

       If  the	value  of any of the limits is unspecified (logically infinite), they will not be
       defined in <limits.h> and the pathconf()  and  fpathconf()  functions  return  -1  without
       changing  errno.  This  can  be distinguished from the case of giving an unrecognized name
       argument because errno is set to [EINVAL] in this case.

       Since -1 is a valid return value for the pathconf() and	fpathconf()  functions,  applica-
       tions  should  set  errno  to  zero before calling them and check errno only if the return
       value is -1.

       For the case of {SYMLINK_MAX}, since both pathconf() and  open()  follow  symbolic  links,
       there is no way that path or fildes could refer to a symbolic link.

FUTURE DIRECTIONS
       None.

SEE ALSO
       confstr()  ,  sysconf() , the Base Definitions volume of IEEE Std 1003.1-2001, <limits.h>,
       <unistd.h>, the Shell and Utilities volume of IEEE Std 1003.1-2001

COPYRIGHT
       Portions of this text are reprinted and	reproduced  in	electronic  form  from	IEEE  Std
       1003.1,	2003  Edition,	Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003  by
       the  Institute  of  Electrical  and  Electronics Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE  and  The  Open  Group
       Standard, the original IEEE and The Open Group Standard is the referee document. The orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				     FPATHCONF(P)
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