NAME

     vkbd — the virtual AT keyboard interface

SYNOPSIS

     device vkbd

DESCRIPTION

     The vkbd interface is a software loopback mechanism that can be loosely described as the virtual AT
     keyboard analog of the pty(4), that is, vkbd does for virtual AT keyboards what the pty(4) driver does for
     terminals.

     The vkbd driver, like the pty(4) driver, provides two interfaces: a keyboard interface like the usual
     facility it is simulating (a virtual AT keyboard in the case of vkbd, or a terminal for pty(4)), and a
     character-special device “control” interface.

     The virtual AT keyboards are named vkbd0, vkbd1, etc., one for each control device that has been opened.

     The vkbd interface permits opens on the special control device /dev/vkbdctl.  When this device is opened,
     vkbd will return a handle for the lowest unused vkbdctl device (use devname(3) to determine which).

     Each virtual AT keyboard supports the usual keyboard interface ioctl(2)s, and thus can be used with
     kbdcontrol(1) like any other keyboard.  The control device supports exactly the same ioctl(2)s as the
     virtual AT keyboard device.  Writing AT scan codes to the control device generates an input on the virtual
     AT keyboard, as if the (non-existent) hardware had just received it.

     The virtual AT keyboard control device, normally /dev/vkbdctl⟨N⟩, is exclusive-open (it cannot be opened if
     it is already open) and is restricted to the super-user.  A read(2) call will return the virtual AT
     keyboard status structure (defined in <dev/vkbd/vkbd_var.h>) if one is available; if not, it will either
     block until one is or return EWOULDBLOCK, depending on whether non-blocking I/O has been enabled.

     A write(2) call passes AT scan codes to be “received” from the virtual AT keyboard.  Each AT scan code must
     be passed as unsigned int.  Although AT scan codes must be passes as unsigned ints, the size of the buffer
     passed to write(2) still should be in bytes, i.e.,

           static unsigned int     codes[] =
           {
           /*      Make    Break */
                   0x1e,   0x9e
           };

           int
           main(void)
           {
                   int     fd, len;

                   fd = open("/dev/vkbdctl0", O_RDWR);
                   if (fd < 0)
                           err(1, "open");

                   /* Note sizeof(codes) - not 2! */
                   len = write(fd, codes, sizeof(codes));
                   if (len < 0)
                           err(1, "write");

                   close(fd);

                   return (0);
           }

     Write will block if there is not enough space in the input queue.

     The control device also supports select(2) for read and write.

     On the last close of the control device, the virtual AT keyboard is removed.  All queued scan codes are
     thrown away.

SEE ALSO

     kbdcontrol(1), atkbdc(4), psm(4), syscons(4), vt(4)

HISTORY

     The vkbd module was implemented in FreeBSD 6.0.

AUTHORS

     Maksim Yevmenkin <m_evmenkin@yahoo.com>

CAVEATS

     The vkbd interface is a software loopback mechanism, and, thus ddb(4) will not work with it.  Current
     implementation of the syscons(4) driver can accept input from only one keyboard, even if it is virtual.
     Thus it is not possible to have both wired and virtual keyboard to be active at the same time.  It is,
     however, in principal possible to obtain AT scan codes from the different sources and write them into the
     same virtual keyboard.  The virtual keyboard state synchronization is the user's responsibility.