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.\" $FreeBSD: src/lib/libc/stdlib/grantpt.3,v 1.3 2003/09/14 13:41:57 ru Exp $
.\"
.Dd February 2, 2005
.Os
.Dt GRANTPT 3
.Sh NAME
.Nm grantpt ,
.Nm posix_openpt ,
.Nm ptsname ,
.Nm ptsname_r ,
.Nm unlockpt
.Nd pseudo-terminal access functions
.Sh SYNOPSIS
.In stdlib.h
.Ft int
.Fo grantpt
.Fa "int fildes"
.Fc
.Ft "char *"
.Fo ptsname
.Fa "int fildes"
.Fc
.Ft "int"
.Fo ptsname_r
.Fa "int fildes"
.Fa "char *buffer"
.Fa "size_t buflen"
.Fc
.Ft int
.Fo unlockpt
.Fa "int fildes"
.Fc
.In stdlib.h
.In fcntl.h
.Ft int
.Fo posix_openpt
.Fa "int oflag"
.Fc
.Sh DESCRIPTION
The
.Fn grantpt ,
.Fn ptsname ,
.Fn ptsname_r ,
.Fn unlockpt ,
and
.Fn posix_openpt
functions allow access to pseudo-terminal devices.
The first four functions accept a file descriptor
that references the master half of a pseudo-terminal pair.
This file descriptor is created with
.Fn posix_openpt .
.Pp
The
.Fn grantpt
function is used to establish ownership and permissions
of the slave device counterpart to the master device
specified with
.Fa fildes .
The slave device's ownership is set to the real user ID
of the calling process; its permissions are set to
user readable-writable and group writable.
The group owner of the slave device is also set to the group
.Dq Li tty
if it exists on the system; otherwise, it
is left untouched.
.Pp
The
.Fn ptsname
and
.Fn ptsname_r
functions return the full pathname of the slave device
counterpart to the master device specified with
.Fa fildes .
This value can be used
to subsequently open the appropriate slave after
.Fn posix_openpt
and
.Fn grantpt
have been called. The
.Fn ptsname
function is not guaranteed to be reentrant or thread safe. The
.Fn ptsname_r
function takes a buffer and length as arguments to avoid this problem.
.Pp
The
.Fn unlockpt
function unlocks the slave pseudo-terminal device associated
with the master device to which
.Fa fildes
refers.
.Pp
The
.Fn posix_openpt
function opens the first available master pseudo-terminal
device and returns a descriptor to it.
The
.Fa oflag
argument
specifies the flags used for opening the device:
.Bl -tag -width ".Dv O_NOCTTY"
.It Dv O_RDWR
Open for reading and writing.
.It Dv O_NOCTTY
If set, do not allow the terminal to become
the controlling terminal for the calling process.
.El
.Sh RETURN VALUES
.Rv -std grantpt unlockpt
.Pp
The
.Fn ptsname
function returns a pointer to the name
of the slave device on success; otherwise a
.Dv NULL
pointer is returned and the global variable
.Va errno
is set to indicate the error.
.Pp
The
.Fn ptsname_r
function returns 0 if successful.  On failure, it returns -1 and the global variable
.Va errno
is set to indicate the error.
.Pp
The
.Fn posix_openpt
function returns a file descriptor to the first
available master pseudo-terminal device on success;
otherwise \-1 is returned and the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn grantpt ,
.Fn ptsname ,
.Fn ptsname_r ,
and
.Fn unlockpt
functions may fail and set
.Va errno
to:
.Bl -tag -width Er
.It Bq Er EINVAL
.Fa fildes
is not a master pseudo-terminal device.
.El
.Pp
In addition, the
.Fn ptsname_r
function may set
.Va errno
to:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Va buffer
argument is NULL.
.El
.Bl -tag -width Er
.It Bq Er ERANGE
The
.Va bufsize
argument is smaller than the length of the string to be returned.
.El
.Pp
In addition, the
.Fn grantpt
function may set
.Va errno
to:
.Bl -tag -width Er
.It Bq Er EACCES
The slave pseudo-terminal device could not be accessed.
.El
.Pp
The
.Fn posix_openpt
function may fail and set
.Va errno
to:
.Bl -tag -width Er
.It Bq Er EINVAL
.Fa oflag
consists of an invalid mode bit.
.It Bq Er EAGAIN
The system has no available pseudo-terminal devices.
.El
.Pp
The
.Fn grantpt ,
.Fn ptsname ,
.Fn ptsname_r ,
and
.Fn unlockpt
functions may also fail and set
.Va errno
for any of the errors specified for the
.Xr fstat 2
system call.
.Pp
The
.Fn posix_openpt
function may also fail and set
.Va errno
for any of the errors specified for the
.Xr open 2
system call.
.Sh LEGACY SYNOPSIS
.Fd #include <stdlib.h>
.Fd #include <fcntl.h>
.Pp
.Ft int
.br
.Fo grantpt
.Fa "int fildes"
.Fc ;
.Pp
.Ft "char *"
.br
.Fo ptsname
.Fa "int fildes"
.Fc ;
.Pp
.Ft int
.br
.Fo unlockpt
.Fa "int fildes"
.Fc ;
.Pp
.Fd #include <fcntl.h>
.Pp
.Ft int
.br
.Fo posix_openpt
.Fa "int oflag"
.Fc ;
.Sh SEE ALSO
.Xr open 2 ,
.Xr pty 4 ,
.Xr tty 4 ,
.Xr compat 5
.Sh STANDARDS
The
.Fn grantpt ,
.Fn ptsname ,
.Fn unlockpt ,
and
.Fn posix_openpt
functions conform to
.St -p1003.1-2001 .