pathconf(2) pathconf(2)
NAME [Toc] [Back]
pathconf(), fpathconf() - get configurable path name variables
SYNOPSIS [Toc] [Back]
#include <unistd.h>
long pathconf(const char *path, int name);
long fpathconf(int fildes, int name);
DESCRIPTION [Toc] [Back]
The pathconf() and fpathconf() functions provide a method for
applications to determine the value of a configurable limit or option
associated with a file or directory (see limits(5) and <unistd.h>).
For pathconf(), the path argument points to the path name of a file or
directory.
For fpathconf(), the fildes argument is an open file descriptor.
For both functions, the name argument represents the variable to be
queried regarding the file or directory to which the other argument
refers.
The following table lists the configuration variables available from
pathconf() and fpathconf(), and lists for each variable the associated
value of the name argument:
Variable | Value of name | Notes
________________________|______________________|_________
LINK_MAX | _PC_LINK_MAX | 1
MAX_CANON | _PC_MAX_CANON | 2
MAX_INPUT | _PC_MAX_INPUT | 2
| _PC_FILESIZEBITS | 3, 4, 10
NAME_MAX | _PC_NAME_MAX | 3, 4
PATH_MAX | _PC_PATH_MAX | 4, 5
PIPE_BUF | _PC_PIPE_BUF | 6
_POSIX_CHOWN_RESTRICTED | _PC_CHOWN_RESTRICTED | 7, 8
_POSIX_NO_TRUNC | _PC_NO_TRUNC | 3, 4
_POSIX_SYNC_IO | _PC_SYNC_IO | 9
_POSIX_VDISABLE | _PC_V_DISABLE | 2
The variables in the table are defined as constants in <limits.h> or
<unistd.h> if they do not vary from one path name to another. The
associated values of the name argument are defined in <unistd.h>.
RETURN VALUE [Toc] [Back]
The following notes further qualify the table above.
1. If path or fildes refers to a directory, the value returned
applies to the directory itself.
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pathconf(2) pathconf(2)
2. If the variable is constant, the value returned is identical
to the variable's definition in <limits.h> or <unistd.h>
regardless of the type of fildes or path. The behavior is
undefined if path or fildes does not refer to a terminal
file.
3. If path or fildes refers to a directory, the value returned
applies to the file names within the directory.
4. If path or fildes does not refer to a directory, pathconf()
or fpathconf() returns -1 and sets errno to EINVAL.
5. If path or fildes refers to a directory, the value returned
is the maximum length of a relative path name when the
specified directory is the working directory.
6. If path refers to a FIFO, or if fildes refers to a pipe or
FIFO, the value returned applies to the pipe or FIFO itself.
If path or fildes refers to a directory, the value returned
applies to any FIFOs that exist or can be created within the
directory. If PIPE_BUF is a constant, the value returned is
identical to the definition of PIPE_BUF in <limits.h>
regardless of the type of fildes or path. The behavior is
undefined for a file other than a directory, FIFO, or pipe.
7. If path or fildes refers to a directory, the value returned
applies to files of any type, other than directories, that
exist or can be created within the directory.
8. _POSIX_CHOWN_RESTRICTED is defined if the privilege group
PRIV_GLOBAL has been granted the CHOWN privilege (see
getprivgrp(2) and chown(2)). In all other cases,
_POSIX_CHOWN_RESTRICTED is undefined and pathconf() or
fpathconf() returns -1 without changing errno. To determine
if chown() can be performed on a file, it is simplest to
attempt the chown() operation and check the return value for
failure or success.
9. _POSIX_SYNC_IO, when defined, determines whether
synchronized IO operations may be performed for the
associated file (see open(2)). If path or fildes refers to
a directory, it is unspecified whether or not the
implementation supports an association of the variable name
with the specified file.
10. For file systems that are not large file enabled, the
_PC_FILESIZEBITS return value will be less than or equal to
32. For file systems that are large file enabled, the
_PC_FILESIZEBITS return value will be between 33 and 63.
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pathconf(2) pathconf(2)
If the variable corresponding to name is not defined for path or
fildes, the pathconf() and fpathconf() functions succeed and return a
value of -1, without changing the value of errno.
Upon any other successful completion, these functions return the value
of the named variable with respect to the specified file or directory,
as described above.
Otherwise, a value of -1 is returned and errno is set to indicate the
error.
ERRORS [Toc] [Back]
The pathconf() and fpathconf() fail if any of the following conditions
are encountered:
[EACCES] A component of the path prefix denies
search permission.
[EBADF] The fildes argument is not a valid open
file descriptor.
[EFAULT] path points outside the allocated
address space of the process.
[EINVAL] The value of name is not valid or the
implementation does not support an
association of the variable name with
the specified file.
[ELOOP] Too many symbolic links were encountered
in translating path.
[ENAMETOOLONG] The length of the specified path name
exceeds PATH_MAX bytes, or the length of
a component of the path name exceeds
NAME_MAX bytes while _POSIX_NO_TRUNC is
in effect.
[ENOENT] The file named by path does not exist
(for example, path is null, or a
component of path does not exist).
[ENOTDIR] A component of the path prefix is not a
directory.
EXAMPLES [Toc] [Back]
The following example sets val to the value of MAX_CANON for the
device file being used as the standard input. If the standard input
is a terminal, this value is the maximum number of input characters
that can be entered on a single input line before typing the newline
character:
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pathconf(2) pathconf(2)
if (isatty(0))
val = fpathconf(0, _PC_MAX_CANON);
The following code segment shows two calls to pathconf. The first
determines whether a file name longer than NAME_MAX bytes will be
truncated to NAME_MAX bytes in the /tmp directory. If so, the second
call is made to determine the actual value of NAME_MAX so that an
error can be printed if a user-supplied file name stored in filebuf
will be truncated in this directory:
extern int errno;
char *filebuf;
errno = 0; /* reset errno */
if ( pathconf("/tmp" _PC_NO_TRUNC) == -1 ) {
/* _POSIX_NO_TRUNC is not in effect for this directory */
if (strlen(filebuf) > pathconf("/tmp", PC_NAME_MAX)) {
fprintf(stderr, "Filename %s too long.\n", filebuf);
/* take error action */
}
else
if (errno) {
perror("pathconf");
/* take error action */
}
}
/* otherwise, _POSIX_NO_TRUNC is in effect for this directory */
if ((fd = open(filebuf, O_CREAT, mode)) < 0)
perror(filebuf);
DEPENDENCIES [Toc] [Back]
NFS
The following error can occur:
[EOPNOTSUPP] path or fildes refers to a file for which a
value for name cannot be determined. In
particular, _PC_LINK_MAX, _PC_NAME_MAX,
_PC_PIPE_BUF, _PC_PATH_MAX, _PC_NO_TRUNC, and
_PC_CHOWN_RESTRICTED, cannot be determined
for an NFS file.
AUTHOR [Toc] [Back]
pathconf() and fpathconf() were developed by HP.
SEE ALSO [Toc] [Back]
chown(2), errno(2), limits(5), unistd(5), termio(7).
STANDARDS CONFORMANCE [Toc] [Back]
pathconf(): AES, SVID3, XPG3, XPG4, FIPS 151-2, POSIX.1, POSIX.2,
POSIX.4
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pathconf(2) pathconf(2)
fpathconf(): AES, SVID3, XPG3, XPG4, FIPS 151-2, POSIX.1, POSIX.2,
POSIX.4
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