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<table class="head">
<tr>
<td class="head-ltitle">VKBD(4)</td>
<td class="head-vol">Device Drivers Manual</td>
<td class="head-rtitle">VKBD(4)</td>
</tr>
</table>
<div class="manual-text">
<section class="Sh">
<h1 class="Sh" id="NAME"><a class="permalink" href="#NAME">NAME</a></h1>
<p class="Pp"><code class="Nm">vkbd</code> — <span class="Nd">the virtual
AT keyboard interface</span></p>
</section>
<section class="Sh">
<h1 class="Sh" id="SYNOPSIS"><a class="permalink" href="#SYNOPSIS">SYNOPSIS</a></h1>
<p class="Pp"><code class="Cd">device vkbd</code></p>
</section>
<section class="Sh">
<h1 class="Sh" id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">DESCRIPTION</a></h1>
<p class="Pp">The <code class="Nm">vkbd</code> interface is a software loopback
mechanism that can be loosely described as the virtual AT keyboard analog of
the <a class="Xr">pty(4)</a>, that is, <code class="Nm">vkbd</code> does for
virtual AT keyboards what the <a class="Xr">pty(4)</a> driver does for
terminals.</p>
<p class="Pp">The <code class="Nm">vkbd</code> driver, like the
<a class="Xr">pty(4)</a> driver, provides two interfaces: a keyboard
interface like the usual facility it is simulating (a virtual AT keyboard in
the case of <code class="Nm">vkbd</code>, or a terminal for
<a class="Xr">pty(4)</a>), and a character-special device
“control” interface.</p>
<p class="Pp">The virtual AT keyboards are named <span class="Pa">vkbd0</span>,
<span class="Pa">vkbd1</span>, etc., one for each control device that has
been opened.</p>
<p class="Pp">The <code class="Nm">vkbd</code> interface permits opens on the
special control device <span class="Pa">/dev/vkbdctl</span>. When this
device is opened, <code class="Nm">vkbd</code> will return a handle for the
lowest unused <span class="Pa">vkbdctl</span> device (use
<a class="Xr">devname(3)</a> to determine which).</p>
<p class="Pp">Each virtual AT keyboard supports the usual keyboard interface
<a class="Xr">ioctl(2)</a>s, and thus can be used with
<a class="Xr">kbdcontrol(1)</a> like any other keyboard. The control device
supports exactly the same <a class="Xr">ioctl(2)</a>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.</p>
<p class="Pp">The virtual AT keyboard control device, normally
<span class="Pa">/dev/vkbdctl</span>⟨<var class="Ar">N</var>⟩,
is exclusive-open (it cannot be opened if it is already open) and is
restricted to the super-user. A <a class="Xr">read(2)</a> call will return
the virtual AT keyboard status structure (defined in
<code class="In"><<a class="In">dev/vkbd/vkbd_var.h</a>></code>) if
one is available; if not, it will either block until one is or return
<code class="Er">EWOULDBLOCK</code>, depending on whether non-blocking I/O
has been enabled.</p>
<p class="Pp">A <a class="Xr">write(2)</a> call passes AT scan codes to be
“received” from the virtual AT keyboard. Each AT scan code
must be passed as <var class="Vt">unsigned int</var>. Although AT scan codes
must be passes as <var class="Vt">unsigned int</var>s, the size of the
buffer passed to <a class="Xr">write(2)</a> still should be in bytes,
i.e.,</p>
<div class="Bd Pp Bd-indent Li">
<pre>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);
}</pre>
</div>
<p class="Pp">Write will block if there is not enough space in the input
queue.</p>
<p class="Pp">The control device also supports <a class="Xr">select(2)</a> for
read and write.</p>
<p class="Pp">On the last close of the control device, the virtual AT keyboard
is removed. All queued scan codes are thrown away.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="SEE_ALSO"><a class="permalink" href="#SEE_ALSO">SEE
ALSO</a></h1>
<p class="Pp"><a class="Xr">kbdcontrol(1)</a>, <a class="Xr">atkbdc(4)</a>,
<a class="Xr">psm(4)</a>, <a class="Xr">syscons(4)</a>,
<a class="Xr">vt(4)</a></p>
</section>
<section class="Sh">
<h1 class="Sh" id="HISTORY"><a class="permalink" href="#HISTORY">HISTORY</a></h1>
<p class="Pp">The <code class="Nm">vkbd</code> module was implemented in
<span class="Ux">FreeBSD 6.0</span>.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="AUTHORS"><a class="permalink" href="#AUTHORS">AUTHORS</a></h1>
<p class="Pp"><span class="An">Maksim Yevmenkin</span>
<<a class="Mt" href="mailto:m_evmenkin@yahoo.com">m_evmenkin@yahoo.com</a>></p>
</section>
<section class="Sh">
<h1 class="Sh" id="CAVEATS"><a class="permalink" href="#CAVEATS">CAVEATS</a></h1>
<p class="Pp">The <code class="Nm">vkbd</code> interface is a software loopback
mechanism, and, thus <a class="Xr">ddb(4)</a> will not work with it. Current
implementation of the <a class="Xr">syscons(4)</a> 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.</p>
</section>
</div>
<table class="foot">
<tr>
<td class="foot-date">August 12, 2004</td>
<td class="foot-os">FreeBSD 15.0</td>
</tr>
</table>
|
