NAME
vkbd
—
the virtual AT keyboard
interface
SYNOPSIS
device vkbd
DESCRIPTION
Thevkbd
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
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.