[patch] Re: [Qemu-devel] Suggestion - trap window-close of VM

[Struan Bartlett <struan@praguespringpeople.org>]

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Hi,

I've attached a patch against the 2005-03-26 snapshot that implements 
two '-on-quit' options for the emulator window: ignore-unless-halted and 
suspend-unless-halted, that aim to make it safe to allow naive users to 
(try to) close the VM window by trapping requests to shutdown and either 
ignoring them or forcing a save of the VM state before obeying them.

Caveat: I'll come clean straight away that the patch is implemented 
using a nasty TARGET_i386-specific hack that detects whether the guest 
operating system has permanently halted by looking to see if the last 
instruction executed was 0xF4 and, if so, whether the IF flag is 
cleared. Saying that, this system appears to work reasonably well on my 
Pentium host running a Windows 2000 guest, but I have not tested it on 
any other systems.

Usage:

1. If you provide naive users with a variation on the following command 
line, then you can let your naive users (try to) close the VM window as 
much as they like. Unless the guest has permanently halted, attempts to 
close the VM window should save the VM state to 'suspended.qemu' in the 
current working directory before qemu exits. The same command line will 
restart the VM where it left off. Then, once the guest has permanently 
halted, qemu will delete the suspended.qemu file so that the next launch 
of qemu will boot afresh:

qemu -hda win2k.raw -m 64 -monitor null -loadvm suspended.qemu -on-quit 
suspend-unless-halted

2. Alternatively, the following command will make qemu ignore the user's 
request to close the emulator window unless the guest has already 
permanently halted:

qemu -hda win2k.raw -m 64 -monitor null -on-quit ignore-unless-halted

3. If you combine this with a test of whether qemu is already running, 
then it should be safe to let naive users try to both launch and to 
close qemu as much as they like. e.g.

killall -0 qemu 2>/dev/null; if [ $? == 1 ]; then qemu -hda win2k.raw -m 
64 -monitor null -loadvm suspended.qemu -on-quit suspend-unless-halted; fi &

4. Finally, if your leave out the -on-quit option altogether, then 
qemu's behaviour should remain completely unchanged.

I hope this is useful for some i386/W2K users out there. Any 
constructive criticism appreciated. If you know how I could improve 
permanent halt detection (that doesn't require in-depth knowledge of APM 
or ACPI) then please let me know.

Struan

Struan Bartlett wrote:

> Ryan Rempel wrote:
>
>>On Mon, Nov 29, 2004 at 21:46:54 +0100, Lennert Buytenhek wrote
>>  
>>
>>>On Mon, Nov 29, 2004 at 08:43:56PM +0000, Richard Neill wrote:
>>>    
>>>
>>>>A thought that occurred to me. If one is running a virtual machine (eg 
>>>>copy of WinXP), then simply closing the qemu window is a really bad 
>>>>idea, since it will effectively crash the guest.
>>>>      
>>>>
>>>Related thought -- it would be way cool if we could make killing qemu
>>>do exactly happens when you press the power button on an ACPI-capable
>>>machine with any recent OS on it (auto shutdown.)
>>>    
>>>
>>I was wondering if anyone has followed up on this suggestion. I'm
>>putting together a Qemu-based setup for some relatively naive users,
>>and ideally I'd like to be able to deal with this in a reasonable
>>elegant way (the ACPI hook sounds very elegant indeed).
>>
>>Alternatively, how do people deal with the problem of naive users who
>>might just close the Qemu window without shutting down the guest
>>properly? I'm working in a KDE environment -- perhaps there is a way
>>in KDE to prevent the close button from appearing? But that wouldn't
>>catch every case either (for instance, if the user were to shut down
>>the host).
>>
> This sounds like a good idea. An alternative solution, that might be 
> more straightforward to implement if Qemu doesn't implement ACPI yet, 
> would be for the kill signal to simply cause Qemu to do the equivalent 
> of entering 'stop' and 'savevm <somefilepath>' into the monitor.
>
>------------------------------------------------------------------------
>
>_______________________________________________
>Qemu-devel mailing list
>Qemu-devel@nongnu.org
>http://lists.nongnu.org/mailman/listinfo/qemu-devel
>  
>

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--- qemu-snapshot-2005-03-26_23/vl.c	Sun Mar 13 17:59:37 2005
+++ qemu-snapshot-2005-03-26_23-on-quit/vl.c	Mon Mar 28 02:06:52 2005
@@ -139,6 +139,9 @@
 int graphic_height = 600;
 int graphic_depth = 15;
 int full_screen = 0;
+#ifdef TARGET_I386
+int on_quit = 0;
+#endif
 TextConsole *vga_console;
 CharDriverState *serial_hds[MAX_SERIAL_PORTS];
 CharDriverState *parallel_hds[MAX_PARALLEL_PORTS];
@@ -2675,6 +2678,17 @@
                         qemu_get_clock(rt_clock));
 }
 
+#ifdef TARGET_I386
+int ishalted() {
+   uint8_t buf[16];
+   uint64_t v;
+	
+   cpu_memory_rw_debug(cpu_single_env, cpu_single_env->eip-1, buf, 16, 0);
+   v = ldub_raw(buf);
+   return (v == 0xf4) && ( !(cpu_single_env->eflags & 0x200) );
+}
+#endif
+
 int main_loop(void)
 {
     int ret, timeout;
@@ -2684,9 +2698,16 @@
         if (vm_running) {
             ret = cpu_exec(env);
             if (shutdown_requested) {
+#ifdef TARGET_I386	       
+	       if( on_quit == 0 || on_quit == 2 || ( on_quit == 1 && ishalted() ) ) {
+#endif		  
                 ret = EXCP_INTERRUPT; 
                 break;
             }
+#ifdef TARGET_I386	       
+ 	       shutdown_requested = 0;
+ 	    }
+#endif
             if (reset_requested) {
                 reset_requested = 0;
                 qemu_system_reset();
@@ -2783,6 +2804,11 @@
            "-std-vga        simulate a standard VGA card with VESA Bochs Extensions\n"
            "                (default is CL-GD5446 PCI VGA)\n"
 #endif
+#ifdef TARGET_I386
+	   "-on-quit [ignore-unless-halted|suspend-unless-halted]\n"
+	   "                select the behaviour when the emulator window is asked to quit\n"
+	   "                (default is none)\n"
+#endif
            "-loadvm file    start right away with a saved state (loadvm in monitor)\n"
            "\n"
            "During emulation, the following keys are useful:\n"
@@ -2864,6 +2890,10 @@
     QEMU_OPTION_full_screen,
     QEMU_OPTION_pidfile,
     QEMU_OPTION_no_kqemu,
+
+#ifdef TARGET_I386	       
+    QEMU_OPTION_on_quit
+#endif     
 };
 
 typedef struct QEMUOption {
@@ -2932,6 +2962,9 @@
     { "loadvm", HAS_ARG, QEMU_OPTION_loadvm },
     { "full-screen", 0, QEMU_OPTION_full_screen },
     { "pidfile", HAS_ARG, QEMU_OPTION_pidfile },
+#ifdef TARGET_I386
+    { "on-quit", HAS_ARG, QEMU_OPTION_on_quit },
+#endif   
 
     /* temporary options */
     { "pci", 0, QEMU_OPTION_pci },
@@ -3383,6 +3416,19 @@
             case QEMU_OPTION_pidfile:
                 create_pidfile(optarg);
                 break;
+#ifdef TARGET_I386   	       
+            case QEMU_OPTION_on_quit:
+	        if(!strcmp(optarg, "ignore-unless-halted")) {
+		   fprintf(stderr, "%s enabled\n", optarg);
+		   on_quit = 1;
+		}
+		else if(!strcmp(optarg, "suspend-unless-halted")) {
+		   fprintf(stderr, "%s enabled\n", optarg);
+		   on_quit = 2;
+		}
+	        else on_quit = 0;
+	        break;
+#endif	       
 #ifdef USE_KQEMU
             case QEMU_OPTION_no_kqemu:
                 kqemu_allowed = 0;
@@ -3696,6 +3742,23 @@
         }
     }
     main_loop();
+
+#ifdef TARGET_I386   
+    if( on_quit == 2 ) {
+       char *f = "suspended.qemu";
+       if( ishalted() ) {
+ 	
+ 	 fprintf(stderr, "VM is halted: removing suspend file %s\n",f);
+ 	 unlink(f);
+ 	 /* qemu_savevm(f); */
+       }
+       else {
+ 	 fprintf(stderr, "Autosaving VM to file %s\n",f);
+ 	 qemu_savevm(f);
+       }
+    }
+#endif   
+   
     quit_timers();
     return 0;
 }