Unix/Linux Go Back    


POSIX 1003.1 - man page for fpathconf (posix section 3p)

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:   man
Select Man Page Set:       apropos Keyword Search (sections above)


FPATHCONF(3P) 			    POSIX Programmer's Manual			      FPATHCONF(3P) 

PROLOG
       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of
       this interface may differ (consult the corresponding Linux  manual  page  for  details  of
       Linux behavior), or the interface may not be implemented on Linux.

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 	| 4,7	       |
		|{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	       |
		|{POSIX2_SYMLINKS}	     | _PC_2_SYMLINKS		| 4	       |
		|{POSIX_ALLOC_SIZE_MIN}      | _PC_ALLOC_SIZE_MIN	| 10	       |
		|{POSIX_REC_INCR_XFER_SIZE}  | _PC_REC_INCR_XFER_SIZE	| 10	       |
		|{POSIX_REC_MAX_XFER_SIZE}   | _PC_REC_MAX_XFER_SIZE	| 10	       |
		|{POSIX_REC_MIN_XFER_SIZE}   | _PC_REC_MIN_XFER_SIZE	| 10	       |
		|{POSIX_REC_XFER_ALIGN}      | _PC_REC_XFER_ALIGN	| 10	       |
		|{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	       |
		|_POSIX_TIMESTAMP_RESOLUTION | _PC_TIMESTAMP_RESOLUTION | 1	       |
		+----------------------------+--------------------------+--------------+
   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 that would not cross any mount points 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.

       10. If  path  or fildes des does not refer to a regular file, it is unspecified whether an
	   implementation supports an association of the variable name with the  specified  file.
	   If  an  implementation supports such an association for other than a regular file, the
	   value returned is unspecified.

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 is described in <limits.h> as a maximum or minimum
       value and the variable has no limit for the path or file descriptor, both  pathconf()  and
       fpathconf()  shall  return  -1 without changing errno.  Note that indefinite limits do not
       imply infinite limits; see <limits.h>.

       If the implementation needs to use path to determine the value of name and the implementa-
       tion  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, pathconf() 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
       implementation's <limits.h> or <unistd.h>.

       If  the	variable corresponding to name is dependent on an unsupported option, the results
       are unspecified.

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.

       EOVERFLOW
	      The value of name is _PC_TIMESTAMP_RESOLUTION and the  resolution  is  larger  than
	      {LONG_MAX}.

       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 a component of a pathname is longer than {NAME_MAX}.

       ENAMETOOLONG
	      The  length  of a pathname exceeds {PATH_MAX}, or pathname resolution of a symbolic
	      link produced an intermediate result with a length that exceeds {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 names an existing file that is neither  a	directory
	      nor  a  symbolic	link  to  a directory, or the path argument contains at least one
	      non-<slash> character and ends with one or more trailing <slash> characters and the
	      last  pathname  component  names an existing file that is neither a directory nor a
	      symbolic link to a directory.

       The fpathconf() function shall fail if:

       EINVAL The value of name is not valid.

       EOVERFLOW
	      The value of name is _PC_TIMESTAMP_RESOLUTION and the  resolution  is  larger  than
	      {LONG_MAX}.

       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
       Application developers should check whether an option, such  as	_POSIX_ADVISORY_INFO,  is
       supported   prior   to	obtaining   and  using	values	for  related  variables  such  as
       {POSIX_ALLOC_SIZE_MIN}.

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 appropriate privileges 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 current working directory of the
       process. 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. Note that imple-
       mentations are allowed to accept pathnames longer than {PATH_MAX} bytes long, but are  not
       allowed	to  return  pathnames  longer than this unless the user specifies a larger buffer
       using a function that provides a buffer size argument.

       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	lifetime  of  the
       process.  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.

       It was the intention of IEEE Std 1003.1d-1999 that the following variables:

	      {POSIX_ALLOC_SIZE_MIN}	 {POSIX_REC_INCR_XFER_SIZE}	{POSIX_REC_MAX_XFER_SIZE}
	      {POSIX_REC_MIN_XFER_SIZE} {POSIX_REC_XFER_ALIGN}

       only applied to regular files, but Note 10 also permits	implementation	of  the  advisory
       semantics  on  other file types unique to an implementation (for example, a character spe-
       cial device).

       The [EOVERFLOW] error for _PC_TIMESTAMP_RESOLUTION cannot occur	on  POSIX-compliant  file
       systems	because  POSIX requires a timestamp resolution no larger than one second. Even on
       32-bit systems, this can be represented without overflow.

FUTURE DIRECTIONS
       None.

SEE ALSO
       chown(), confstr(), sysconf()

       The Base Definitions volume of POSIX.1-2008, <limits.h>, <unistd.h>

       The Shell and Utilities volume of POSIX.1-2008, getconf

COPYRIGHT
       Portions of this text are reprinted and	reproduced  in	electronic  form  from	IEEE  Std
       1003.1,	2013  Edition,	Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013  by  the
       Institute  of  Electrical  and  Electronics  Engineers,	Inc and The Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any  discrep-
       ancy  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  original	Standard  can  be
       obtained online at http://www.unix.org/online.html .

       Any  typographical  or  formatting errors that appear in this page are most likely to have
       been introduced during the conversion of the source files to man page  format.  To  report
       such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group			       2013				      FPATHCONF(3P)
Unix & Linux Commands & Man Pages : ©2000 - 2017 Unix and Linux Forums


All times are GMT -4. The time now is 02:03 AM.