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.\"	$NetBSD: pathconf.2,v 1.2 1995/02/27 12:35:22 cgd Exp $
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.\"	@(#)pathconf.2	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt PATHCONF 2
.Os BSD 4
.Sh NAME
.Nm fpathconf ,
.Nm pathconf
.Nd get configurable pathname variables
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft long
.Fo fpathconf
.Fa "int fildes"
.Fa "int name"
.Fc
.Ft long
.Fo pathconf
.Fa "const char *path"
.Fa "int name"
.Fc
.Sh DESCRIPTION
.Pp
The
.Fn pathconf
and
.Fn fpathconf
functions provides 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 fildes
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 <unistd.h> .
.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 file name.
.It Li _PC_PATH_MAX
The maximum number of bytes in a pathname.
.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 file names longer than KERN_NAME_MAX are truncated.
.It Li _PC_VDISABLE
Returns the terminal character disabling value.
.It Li _PC_XATTR_SIZE_BITS
Returns the number of bits used to store maximum extended 
attribute size in bytes.  For example, if the maximum 
attribute size supported by a file system is 128K, the 
value returned will be 18.  However a value 18 can mean 
that the maximum attribute size can be anywhere from 
(256KB - 1) to 128KB.  As a special case, the resource 
fork can have much larger size, and some file system 
specific extended attributes can have smaller and preset 
size; for example, Finder Info is always 32 bytes.
.It Li _PC_MIN_HOLE_SIZE
If a file system supports the reporting of holes (see
.Xr lseek 2 ) ,
.Fn pathconf
and
.Fn fpathconf
return a positive number that represents the minimum hole size returned in
bytes.
The offsets of holes returned will be aligned to this same value.
A special value of 1 is returned if the file system does not specify the minimum
hole size but still reports holes.
.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 ENAMETOOLONGAA
.\" ===========
.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.
.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 occurs while reading from or writing to the file system.
.\" ===========
.It Bq Er ELOOP
Too many symbolic links are encountered in translating the pathname.
This is taken to be indicative of a looping symbolic link.
.\" ===========
.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 ENAMETOOLONGAA
.Fn fpathconf
will fail if:
.\" ===========
.It Bq Er EBADF
.Fa fildes
is not a valid open file descriptor.
.\" ===========
.It Bq Er EIO
An I/O error occurs while reading from or writing to the file system.
.El
.Sh SEE ALSO
.Xr sysctl 3
.Sh HISTORY
The
.Nm pathconf
and
.Nm fpathconf
functions first appeared in 4.4BSD.