NetBSD/lib/libc/sys/pathconf.2

.\"	$NetBSD: pathconf.2,v 1.21 2008/08/14 18:00:08 wiz Exp $
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.\"	@(#)pathconf.2	8.1 (Berkeley) 6/4/93
.\"
.Dd August 14, 2008
.Dt PATHCONF 2
.Os
.Sh NAME
.Nm pathconf ,
.Nm fpathconf
.Nd get configurable pathname variables
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft long
.Fn pathconf "const char *path" "int name"
.Ft long
.Fn fpathconf "int fd" "int name"
.Sh DESCRIPTION
The
.Fn pathconf
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
.Nm pathconf ,
the
.Fa path
argument is the name of a file or directory.
For
.Nm 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
.Li \*[Lt]unistd.h\*[Gt] .
.Pp
The available values are as follows:
.Pp
.Bl -tag -width "123456"
.Pp
.It Li _PC_LINK_MAX
The maximum file link count.
.It Li _PC_MAX_CANON
The maximum number of bytes in terminal canonical input line.
.It Li _PC_MAX_INPUT
The minimum maximum number of bytes for which space is available in
a terminal input queue.
.It Li _PC_NAME_MAX
The maximum number of bytes in a filename,
not including a terminating null character.
.It Li _PC_PATH_MAX
The maximum number of bytes in a pathname,
including the terminating null character.
.It Li _PC_PIPE_BUF
The maximum number of bytes which will be written atomically to a pipe.
.It Li _PC_CHOWN_RESTRICTED
Return 1 if appropriate privileges are required for the
.Xr chown 2
system call, otherwise 0.
.It Li _PC_NO_TRUNC
Return 1 if filenames longer than
.Dv {NAME_MAX}
are truncated.
.It Li _PC_VDISABLE
Returns the terminal character disabling value.
.It Li _PC_SYNC_IO
Returns 1 if synchronized I/O is supported, otherwise 0.
.It Li _PC_FILESIZEBITS
If the maximum size file that could ever exist on the mounted file system is
.Dv maxsize ,
then the returned value is 2 plus the floor of the base 2 logarithm of
.Dv maxsize .
.It Li _PC_SYMLINK_MAX
The maximum number of bytes in a symbolic link.
.It Li _PC_2_SYMLINKS
When referring to a directory the system supports the creation of symbolic
links within that directory; for nondirectory files, the meaning of
.Dv {_PC_2_SYMLINKS}
is undefined.
.El
.Sh RETURN VALUES
If the call to
.Nm pathconf
or
.Nm 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
.Nm pathconf
and
.Nm 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, or
the implementation does not support an association of the variable
name with the associated file.
.El
.Pp
.Fn pathconf
will fail if:
.Bl -tag -width ENAMETOOLONGAA
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 255 characters,
or an entire path name exceeded 1023 characters.
.It Bq Er ENOENT
The named file does not exist.
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.El
.Pp
.Bl -tag -width [EFAULT]
.Fn fpathconf
will fail if:
.It Bq Er EBADF
.Fa fd
is not a valid open file descriptor.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.El
.Sh SEE ALSO
.Xr sysctl 3
.Sh STANDARDS
The
.Fn pathconf
and
.Fn fpathconf
functions conform to
.St -p1003.1-90 .
.Sh HISTORY
The
.Nm pathconf
and
.Nm fpathconf
functions first appeared in
.Bx 4.4 .