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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 dif-
       fer (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 configurable 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  directory.  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 directory 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 implementation 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 path-
           name 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 refer-
           enced 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 directo-
           ries, 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  associa-
           tion 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 fpath-
       conf() 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,
       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 implementation does not sup-
       port 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 indicate 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>.

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 sub-
              stituted 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 sys-
       tem.

       Therefore, various useful values can be queried on any pathname or file descriptor, assuming that the appropri-
       ate 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 path-
       conf(), 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  imple-
       mentation,  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, applications 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, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions 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 Stan-
       dard, the original IEEE and The Open Group Standard is the referee  document.  The  original  Standard  can  be
       obtained online at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group                  2003                        FPATHCONF(3P)