VT(7I) Ioctl Requests VT(7I)

vt —
illumos virtual console interface

#include <sys/kd.h>
#include <sys/vt.h>

The virtual console device driver — also known as virtual terminal (VT) — is a layer of management functions that provides facilities to support and switch between multiple screen faces on a single physical device.

VT's are accessed in the same way as other devices. The open(2) system call is used to open the virtual console and read(2), write(2) and ioctl(2) are used in the normal way and support the functionality of the underlying device. In addition, some virtual console-specific ioctls are provided and described below.

The VT provides a link between different screen faces and the device. The active virtual console corresponds to the currently visible screen face. Device input is directed to the active console and any device-specific modes that change on a per virtual terminal basis are set to the characteristics associated with the active console.

You manage VT's by intercepting keyboard sequences (“hot key”). To maintain consistency with Xserver, the virtual console device driver supports the Ctrl, Alt, F# and arrow keys.

The sequence AltL + F# (where AltL represents the left Alt key and F# represents function keys 1 through 12) is used to select virtual console 1-12. The sequence AltGraph + F# (where AltGraph represents the right Alt key and F# represent function keys 1 through 12) is for virtual console 13-24. Alt + F1 chooses the system console (also known as virtual console 1). The sequence Alt + → (where "→" represents the right directional arrow) selects the next VT in a circular ring fashion and Alt + ← (where "←" represents the left directional arrow) changes to the previous console in a circular fashion. The sequence Alt + ↑ (where "↑" represents the up directional arrow) is for the last used console.

Virtual console switching can be done automatically (VT_AUTO) on receipt of a “hot-key” or by the process owning the VT (VT_PROCESS). When performed automatically, the process associated with the virtual console is unaware of the switch. Saving and restoring the device are handled by the underlying device driver and the virtual console manager. Note that automatic switching is the default mode.

When a “hot-key” is sent when in process-controlled switch mode, the process owning the VT is sent a signal (relsig) it has specified to the virtual console manager (see signal(3C)) requesting the process to release the physical device. At this point, the virtual console manager awaits the VT_RELDISP ioctl from the process. If the process refuses to release the device (meaning the switch does not occur), it performs a VT_RELDISP ioctl with an argument of 0 (zero). If the process desires to release the device, it saves the device state (keyboard, display, and I/O registers) and then performs a VT_RELDISP with an argument of 1 to complete the switch.

A ring of VT's can contain intermixed auto mode and process control mode consoles. When an auto mode process becomes active, the underlying device driver and the virtual console manager handle the restoring of the device. Process control mode processes are sent a specified signal (acqsig) when they become the active console. The process then restores the device state (keyboard, display, and I/O registers) and performs VT_RELDISP ioctl with an argument of VT_ACKACQ to complete the switching protocol.

The modify-operations ioctls (VT_SETMODE, VT_RELDISP, VT_WAITACTIVE, KDSETMODE) check if the VT is the controlling tty of the calling process. If not, the sys_devices privilege is enforced. VT_ACTIVATE requires the sys_devices privilege. Note that there is no controlling tty and privilege check for query/view operations.

The following ioctls apply to devices that support virtual consoles:
Queries to determine if VT functionality is available on the system. The argument is a pointer to an integer. If VT functionality is available, the integer is 1, otherwise it is 0.
Finds an available VT. The argument is a pointer to an integer. The integer is filled in with the number of the first available console that no other process has open (and hence, is available to be opened). If there are no available VT's, -1 is filled in.
Determines the VT's current mode, either VT_AUTO or VT_PROCESS. The argument is the address of the following structure, as defined in <sys/vt.h> 
struct vt_mode {
      char mode;     /* VT mode */
      char waitv;    /* not used */
      short relsig;  /* signal to use for release request */
      short acqsig;  /* signal to use for display acquired */
      short frsig;   /* not used */
}

/* Virtual console Modes */
#define	VT_AUTO		0 /* automatic VT switching	*/
#define	VT_PROCESS	1 /* process controls switching */

The structure will be filled in with the current value for each field.

Sets the VT mode. The argument is a pointer to a vt_mode structure as defined above. The structure should be filled in with the desired mode. If process-control mode is specified, the signals used to communicate with the process should be specified. If any signals are not specified (value is zero), the signal default is SIGUSR1 (for relsig and acqsig).
Tells the VT manager if the process releases (or refuses to release) the display. An argument of 1 indicates the VT is released. An argument of 0 indicates refusal to release. The VT_ACKACQ argument indicates if acquisition of the VT has been completed.
Makes the VT specified in the argument the active VT (in the same manner as if a hotkey initiated the switch). If the specified VT is not open or does not exist, the call fails and errno is set to ENXIO.
If the specified VT is currently active, this call returns immediately. Otherwise, it sleeps until the specified VT becomes active, at which point it returns.
Obtains the active VT number and a list of open VTs. The argument is an address to the following structure: 
struct vt_stat {
    unsigned short v_active, /* number of the active VT */
	           v_signal, /* not used */
                   /*
                    * count of open VTs.  For every 1 in this
                    * field, there is an open VT
                    */
	           v_state;
}

With VT_GETSTATE, the VT manager first gets the number of the active VT, then determines the number of open VTs in the system and sets a 1 for each open VT in v_state. Next, the VT manager transfers the information in structure vt_stat passed by the user process.

Obtains the text/graphics mode associated with the VT. 
#define KD_TEXT         0
#define KD_GRAPHICS     1
Sets the text/graphics mode to the VT.
indicates that console text is displayed on the screen. Normally KD_TEXT is combined with VT_AUTO mode for text console terminals, so that the console text display automatically is saved and restored on the hot key screen switches.

KD_GRAPHICS indicates that the user/application (usually Xserver) has direct control of the display for this VT in graphics mode. Normally KD_GRAPHICS is combined with VT_PROCESS mode for this VT indicating direct control of the display in graphics mode. In this mode, all writes to the VT using the write system call are ignored, and you must save and restore the display on the hot key screen switches.

When the mode of the active VT is changed from KD_TEXT to KD_GRAPHICS or a VT of KD_GRAPHICS mode is made active from a previous active VT of KD_TEXT mode, the virtual console manager initiates a KDSETMODE ioctl with KD_GRAPHICS as the argument to the underlying console frame buffer device indicating that current display is running into graphics mode.

When the mode of the active VT is changed from KD_GRAPHICS to KD_TEXT or a VT of KD_TEXT mode is actived from a previous active VT of KD_GRAPHICS mode, the virtual console manager initiates a KDSETMODE ioctl with KD_TEXT as the argument to the underlying console frame buffer device indicating that current display is running into console text mode.

/dev/vt/#
VT devices.

ioctl(2), signal(3C), wscons(7D)

By default, there are only five virtual console instance login prompts running on /dev/vt/# (where "#" represents 2 to 6) in addition to the system console running on /dev/console. Normally Xorg uses the seventh virtual console (/dev/vt/7). To switch from consoles to Xserver (which normally picks up the first available virtual console), use [ Ctrl + ] Alt + F7 . 
# svcs | grep login
online         17:49:11 svc:/system/console-login:default
online         17:49:11 svc:/system/console-login:vt2
online         17:49:11 svc:/system/console-login:vt3
online         17:49:11 svc:/system/console-login:vt4
online         17:49:11 svc:/system/console-login:vt5
online         17:49:11 svc:/system/console-login:vt6

console-login:default is for the system console, others for virtual consoles.

You can manage virtual consoles using the service management facility, smf(5):

# svccfg -s console-login add vt8
# svccfg -s console-login:vt8 setprop \
  ttymon/device=astring: "/dev/vt/8"
# svcadm enable console-login:vt8
February 17, 2020 illumos