xref: /freebsd/lib/libc/stdlib/ptsname.3 (revision a5ed6a815e38d6c622cd97a6020592ded579cf7a)

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.Dd October 14, 2023
.Dt PTSNAME 3
.Os
.Sh NAME
.Nm grantpt ,
.Nm ptsname ,
.Nm ptsname_r ,
.Nm unlockpt
.Nd pseudo-terminal access functions
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft int
.Fn grantpt "int fildes"
.Ft "char *"
.Fn ptsname "int fildes"
.Ft "int"
.Fn ptsname_r "int fildes" "char *buffer" "size_t buflen"
.Ft int
.Fn unlockpt "int fildes"
.Sh DESCRIPTION
The
.Fn grantpt ,
.Fn ptsname ,
and
.Fn unlockpt
functions allow access to pseudo-terminal devices.
These three functions accept a file descriptor that references the
master half of a pseudo-terminal pair.
This file descriptor is created with
.Xr posix_openpt 2 .
.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, and the 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 .
.Pp
The
.Fn ptsname
function returns 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
.Xr posix_openpt 2
and
.Fn grantpt
have been called.
.Pp
The
.Fn ptsname_r
function is the thread-safe version of
.Fn ptsname .
The caller must provide storage for the results of the full pathname of
the slave device in the
.Fa buffer
and
.Fa bufsize
arguments.
.Pp
The
.Fn unlockpt
function clears the lock held on the pseudo-terminal pair
for the master device specified with
.Fa fildes .
.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.
.Pp
The
.Fn ptsname_r
function returns the value 0 if successful;
otherwise a nonzero value is returned and the global variable
.Va errno
is set to indicate the error.
Note:
.Fn ptsname_r
was previously documented as returning -1 on error.
In the future it will be changed to return an error number, for POSIX
compatibility.
Therefore, callers should not check for -1.
.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 EBADF
.Fa fildes
is not a valid open file descriptor.
.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 ERANGE
The buffer was too small.
.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
.Sh SEE ALSO
.Xr posix_openpt 2 ,
.Xr pts 4 ,
.Xr tty 4
.Sh STANDARDS
The
.Fn ptsname
function conforms to
.St -p1003.1-2008 .
.Pp
This implementation of
.Fn grantpt
and
.Fn unlockpt
does not conform to
.St -p1003.1-2008 ,
because it depends on
.Xr posix_openpt 2
to create the pseudo-terminal device with proper permissions in place.
It only validates whether
.Fa fildes
is a valid pseudo-terminal master device.
Future revisions of the specification will likely allow this behaviour,
as stated by the Austin Group.
.Sh HISTORY
The
.Fn grantpt ,
.Fn ptsname
and
.Fn unlockpt
functions appeared in
.Fx 5.0 .