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.\"	@(#)pathconf.2	8.1 (Berkeley) 6/4/93
.\"
.Dd $Mdocdate: May 18 2024 $
.Dt PATHCONF 2
.Os
.Sh NAME
.Nm pathconf ,
.Nm pathconfat ,
.Nm fpathconf
.Nd get configurable pathname variables
.Sh SYNOPSIS
.In unistd.h
.Ft long
.Fn pathconf "const char *path" "int name"
.Ft long
.Fn fpathconf "int fd" "int name"
.In fcntl.h
.Ft long
.Fn pathconfat "int fd" "const char *path" "int name" "int flag"
.Sh DESCRIPTION
The
.Fn pathconf ,
.Fn pathconfat ,
and
.Fn fpathconf
functions provide a method for applications to determine the current
value of a configurable system limit or option variable associated
with a pathname or file descriptor.
.Pp
For
.Fn pathconf ,
the
.Fa path
argument is the name of a file or directory.
For
.Fn fpathconf ,
the
.Fa fd
argument is an open file descriptor.
The
.Fa name
argument specifies the system variable to be queried.
Symbolic constants for each name value are found in the include file
.In unistd.h .
.Pp
The available values are as follows:
.Bl -tag -width "123456"
.It Dv _PC_LINK_MAX
The maximum file link count.
.It Dv _PC_MAX_CANON
The maximum number of bytes in a terminal canonical input line.
.It Dv _PC_MAX_INPUT
The maximum number of bytes for which space is available in
a terminal input queue.
.It Dv _PC_NAME_MAX
The maximum number of bytes in a file name.
.It Dv _PC_PATH_MAX
The maximum number of bytes in a pathname.
.It Dv _PC_PIPE_BUF
The maximum number of bytes which will be written atomically to a pipe.
.It Dv _PC_CHOWN_RESTRICTED
Returns 1 if appropriate privileges are required for the
.Xr chown 2
system call, otherwise 0.
.St -p1003.1-2001
requires appropriate privilege in all cases, but this behavior was
optional in prior editions of the standard.
.It Dv _PC_NO_TRUNC
Returns 1 if attempts to use pathname components longer than
.Brq Dv NAME_MAX
will result in an
.Bq Er ENAMETOOLONG
error; otherwise, such components will be truncated to
.Brq Dv NAME_MAX .
.St -p1003.1-2001
requires the error in all cases, but this behavior was optional in prior
editions of the standard, and some non-POSIX-compliant file systems do not
support this behavior.
.It Dv _PC_VDISABLE
Returns the terminal character disabling value.
.It Dv _PC_2_SYMLINKS
Returns 1 if the filesystem supports the creation of symbolic links
within the specified directory; the meaning of
.Dv _PC_2_SYMLINKS
is unspecified for non-directory files.
.It Dv _PC_ALLOC_SIZE_MIN
Minimum number of bytes of storage allocated for any portion of a file.
.It Dv _PC_ASYNC_IO
Returns 1 if asynchronous I/O is supported, otherwise 0.
.It Dv _PC_FILESIZEBITS
Number of bits needed to represent the maximum file size.
.It Dv _PC_PRIO_IO
Returns 1 if prioritized I/O is supported, otherwise 0.
.It Dv _PC_REC_INCR_XFER_SIZE
Recommended increment for file transfer sizes between _PC_REC_MIN_XFER_SIZE
and _PC_REC_MAX_XFER_SIZE.
.It Dv _PC_REC_MAX_XFER_SIZE
Maximum recommended file transfer size.
.It Dv _PC_REC_MIN_XFER_SIZE
Minimum recommended file transfer size.
.It Dv _PC_REC_XFER_ALIGN
Recommended file transfer buffer alignment.
.It Dv _PC_SYMLINK_MAX
Maximum number of bytes in a symbolic link.
.It Dv _PC_SYNC_IO
Returns 1 if synchronized I/O is supported, otherwise 0.
.It Dv _PC_TIMESTAMP_RESOLUTION
The resolution in nanoseconds of file timestamps.
.El
.Pp
The
.Fn pathconfat
function is equivalent to
.Fn pathconf
except in the case where
.Fa path
specifies a relative path.
In this case the file to be changed is determined relative to the directory
associated with the file descriptor
.Fa fd
instead of the current working directory.
.Pp
If
.Fn pathconfat
is passed the special value
.Dv AT_FDCWD
(defined in
.In fcntl.h )
in the
.Fa fd
parameter, the current working directory is used.
If
.Fa flag
is also zero, the behavior is identical to a call to
.Fn pathconf .
.Pp
The
.Fa flag
argument is the bitwise OR of zero or more of the following values:
.Pp
.Bl -tag -width AT_SYMLINK_NOFOLLOW -offset indent -compact
.It Dv AT_SYMLINK_NOFOLLOW
If
.Fa path
names a symbolic link, then the system variable for the symbolic
link is queried.
.El
.Sh RETURN VALUES
If the call to
.Fn pathconf ,
.Fn pathconfat ,
or
.Fn fpathconf
is not successful, \-1 is returned and
.Va errno
is set appropriately.
Otherwise, if the variable is associated with functionality that does
not have a limit in the system, \-1 is returned and
.Va errno
is not modified.
Otherwise, the current variable value is returned.
.Sh ERRORS
If any of the following conditions occur, the
.Fn pathconf ,
.Fn pathconfat ,
and
.Fn fpathconf
functions shall return \-1 and set
.Va errno
to the corresponding value.
.Bl -tag -width Er
.It Bq Er EINVAL
The value of the
.Fa name
argument is invalid.
.It Bq Er EINVAL
The implementation does not support an association of the variable
name with the associated file.
.It Bq Er EIO
An I/O error occurred while reading from the file system.
.El
.Pp
.Fn pathconf
and
.Fn pathconfat
will fail if:
.Bl -tag -width Er
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded
.Dv NAME_MAX
characters (but see
.Dv _PC_NO_TRUNC
above), or an entire pathname (including the terminating NUL)
exceeded
.Dv PATH_MAX
bytes.
.It Bq Er ENOENT
The named file does not exist.
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EFAULT
.Fa path
points outside the process's allocated address space.
.El
.Pp
Additionally, the
.Fn pathconfat
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The value of the
.Fa flag
argument was neither zero nor
.Dv AT_SYMLINK_NOFOLLOW .
.It Bq Er EBADF
The
.Fa path
argument specifies a relative path and the
.Fa fd
argument is neither
.Dv AT_FDCWD
nor a valid file descriptor.
.It Bq Er ENOTDIR
The
.Fa path
argument specifies a relative path and the
.Fa fd
argument is a valid file descriptor but it does not reference a directory.
.It Bq Er EACCES
The
.Fa path
argument specifies a relative path but search permission is denied
for the directory which the
.Fa fd
file descriptor references.
.El
.Pp
.Fn fpathconf
will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa fd
is not a valid open file descriptor.
.El
.Sh SEE ALSO
.Xr sysctl 2 ,
.Xr sysconf 3
.Sh STANDARDS
The
.Fn pathconf
and
.Fn fpathconf
functions conform to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn pathconf
and
.Fn fpathconf
functions first appeared in
.Bx 4.4 .
The
.Fn pathconfat
function first appeared in
.Ox 7.6 .