切换虚拟终端简介(053556)

1、切换虚拟终端概述linux 使用虚拟终端，这些虚拟终端对应 /dev/tty1/dev/tty8, 它们由系统初始化时翻开。 这个过程也在键盘的中断效劳程序中完成。用户用ALT+1.8 或 ALT+ 箭头来切换终端。每个虚拟终端对应一个 tty_struct 和一个 termios 结构。 Termios 结构存储输入输出及控制模式， 一些底层参数。 Tty_struct 和终端的关系如同 task_struct 和进程的关系。一个 tty 被翻开， 就对应一个tty_stract,对终端的一切处理都围绕tty_strct进行。Termios也被tty_struct的一个指针指向。当然， tt

2、y_struct 和 termios 结构相对独立， tty 被完全关闭时， tty_struct 也就不 在存在，而 termios 依然存在。另：1 与虚拟终端相对的是实终端。它对应/dev/tty0 或 /dev/console 二者设备号均为4,02 0 35系统初始时 tty 的初始化分早期和晚期。早期初始化支持实终端，晚期初始化 支持虚拟终端。此时 /dev/tty0 或 /dev/console 对应当前终端。2 伪终端正如其名， 与控制台终端除了最高层的输入输出功能类似外， 底层的实现大相 径庭。终端切换的流程：Keyboard, in terruptKey_ha ndler(

3、do_c ons)Set_c on slewant_con sole = nr; mark_bh(CONSOLE_BH);static void keyboard_ in terrupt(i nt irq, void *dev_id, struct pt_regs *regs) han dle_sca ncode(sca ncode);(*key_handlertype)(keysym & Oxff, up_flag);k_hand key_handlerkeyboard.c键盘特殊输入的特殊处理函数数组。static k_ha nd key_ha ndler16 = do_self,

4、 do_fn, do_spec, do_pad, do_dead, do_c ons, do_cur, do_shift, do_meta, do_ascii, do_lock, do_lowercase, do_slock,do_ignore, do_ignore, do_ignore ;do_cons()改变终端的最上层函数 keyboard.c static void do_cons(unsigned char value, char up_flag) if (up_flag) return;set_console(value);set_console设置 want_console 为欲

5、切换到的终端。设置 console 的 bottom half 标志。kbd_kern.hextern inline void set_console(int nr) want_console = nr; mark_bh(CONSOLE_BH);console_bh ()console.cstatic void console_bh(void)是否要切换 consoleif (want_console >= 0) if (want_console != fg_console) change_console(want_console);/* we only changed when the

6、 console had already been allocated - a new console is not created in an interrupt routine */want_console = -1;if (do_poke_blanked_console) /* do not unblank for a LED change */ do_poke_blanked_console = 0;poke_blanked_console();change_console ()tty_io.c 切换终端的实际动作。 void change_console(unsigned int n

7、ew_console) if (new_console = fg_console) | (vt_dont_switch)return;if (!vc_cons_allocated(new_console)return;/*If this vt is in process mode, then we need to handshake with什么模式？ 在此模式下，不能直接切换，要等待！* that process before switching. Essentially, we store where that* vt wants to switch to and wait for it

8、to tell us when it's done* (via VT_RELDISP ioctl).* We also check to see if the controlling process still exists.控制进程* If it doesn't, we reset this vt to auto mode and continue.AAAAAAAAAA什么模式？* This is a cheap way to track process control. The worst thing* that can happen is: we send a signa

9、l to a process, it dies, and* the switch gets "lost" waiting for a response; hopefully, the* user will try again, we'll detect the process is gone (unless* the user waits just the right amount of time :-) and revert the* vt to auto control.*/VT_PROCESS 模式的处理。在此模式下，不能直接切换，要等待！if (vt_con

10、sfg_console->vt_mode.mode = VT_PROCESS)/* Send the signal as privileged - kill_proc() will* tell us if the process has gone or something else* is awry */ if (kill_proc(vt_consfg_console->vt_pid, vt_consfg_console->vt_mode.relsig, 1) = 0)/* It worked. Mark the vt to switch to and* return. Th

11、e process needs to send us a* VT_RELDISP ioctl to complete the switch.*/ vt_consfg_console->vt_newvt = new_console; return;/* The controlling process has died, so we revert back to* normal operation. In this case, we'll also change back* to KD_TEXT mode. I'm not sure if this is strictly c

12、orrect* but it saves the agony when the X server dies and the screen* remains blanked due to KD_GRAPHICS! It would be nice to do* this outside of VT_PROCESS but there is no single process* to account for and tracking tty count may be undesirable.*/reset_vc(fg_console);/* Fall through to normal (VT_A

13、UTO) handling of the switch.*/在 KD_GRAPHICS+VT_AUTO 模式下忽略所有终端切换。if (vt_consfg_console->vc_mode = KD_GRAPHICS)return;complete_change_console(new_console);相关函数与变量判断新的虚拟终端是否存在。int vc_cons_allocated(unsigned int i)/console.creturn (i < MAX_NR_CONSOLES && vc_consi.d);重设新的虚拟终端的 vc_date 结构。vo

14、id reset_vc(unsigned int new_console)/tty_io.c vt_consnew_console->vc_mode = KD_TEXT; kbd_tablenew_console.kbdmode = VC_XLATE; vt_consnew_console->vt_mode.mode = VT_AUTO; vt_consnew_console->vt_mode.waitv = 0; vt_consnew_console->vt_mode.relsig = 0; vt_consnew_console->vt_mode.acqsig

15、= 0; vt_consnew_console->vt_mode.frsig = 0; vt_consnew_console->vt_pid = -1; vt_consnew_console->vt_newvt = -1; reset_palette (new_console) ;complete_change_console ()切换终端的实际动作。tty_io.cvoid complete_change_console(unsigned int new_console)unsigned char old_vc_mode;if (new_console = fg_conso

16、le) | (vt_dont_switch) return;if (!vc_cons_allocated(new_console)return;l ast_console = fg_console;/* If we're switching, we could be going from KD_GRAPHICS to* KD_TEXT mode or vice versa, which means we need to blank or* unblank the screen later.*/old_vc_mode = vt_consfg_console->vc_mode;根据

17、new_console 重设显示器。update_screen(new_console);/* If this new console is under process control, send it a signal* telling it that it has acquired. Also check if it has died and* clean up (similar to logic employed in change_console()*/if (vt_consnew_console->vt_mode.mode = VT_PROCESS)/* Send the si

18、gnal as privileged - kill_proc() will* tell us if the process has gone or something else* is awry*/if (kill_proc(vt_consnew_console->vt_pid,vt_consnew_console->vt_mode.acqsig,1) != 0)/* The controlling process has died, so we revert back to* normal operation. In this case, we'll also chang

19、e back* to KD_TEXT mode. I'm not sure if this is strictly correct* but it saves the agony when the X server dies and the screen* remains blanked due to KD_GRAPHICS! It would be nice to do* this outside of VT_PROCESS but there is no single process* to account for and tracking tty count may be und

20、esirable.*/reset_vc(new_console);/* We do this here because the controlling process above may have* gone, and so there is now a new vc_mode*/if (old_vc_mode != vt_consnew_console->vc_mode)if (vt_consnew_console->vc_mode = KD_TEXT)文本模式do_unblank_screen();else图形模式do_blank_screen(1);/* Set the co

21、lour palette for this VT */if (vt_consnew_console->vc_mode = KD_TEXT)set_palette() ;/* Wake anyone waiting for their VT to activate*/ vt_wake_waitactive(); return; 相关函数与变量 #define vt_wake_waitactive() wake_up(&vt_activate_queue)update_screen ()console.c 重设屏幕。void update_screen(int new_console)static int lock = 0; lock 保证该函数不会被重入。if (new_console = fg_console | lock) return;if (!vc_cons_allocated(new_console) /* strange . */printk("update_screen: tty %d not alloca