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[Qemu-devel] Re: [PATCH] Add monitor command for system_reboot


From: Anthony Liguori
Subject: [Qemu-devel] Re: [PATCH] Add monitor command for system_reboot
Date: Fri, 08 May 2009 12:38:17 -0500
User-agent: Thunderbird 2.0.0.21 (X11/20090320)

Ryan Harper wrote:
* Anthony Liguori <address@hidden> [2009-05-08 12:00]:
Ryan Harper wrote:
Add a new monitor command (system_reboot) for a soft reboot which uses
system_powerdown to trigger ACPI shutdown in the guest and once shutdown is
complete, trigger a reset instead of exiting qemu.

Depends on commit a6d6552426dcbf726e5549f08b70c9318d6be14b which enabled ACPI
power button support.

Tested with Ubuntu 9.04 64-bit guest.

Signed-off-by: Ryan Harper <address@hidden>

diff --git a/hw/acpi.c b/hw/acpi.c
index dbaf18a..346d100 100644
--- a/hw/acpi.c
+++ b/hw/acpi.c
@@ -151,7 +151,13 @@ static void pm_ioport_writew(void *opaque, uint32_t addr, uint32_t val)
                sus_typ = (val >> 10) & 7;
                switch(sus_typ) {
                case 0: /* soft power off */
-                    qemu_system_shutdown_request();
+ /* after powerdown, if on system_reboot path, call reset + instead of shutdown */
+                    if (qemu_reboot_requested()) {
+                        qemu_system_reset_request();
+                    } else {
+                        qemu_system_shutdown_request();
+                    }
                    break;
If qemu_shutdown_requested(), then we'll immediately shutdown the system.

Right, but this request happens after we've sent the ACPI powerdown
event.  After we've done the powerdown (acpi aware guests can do a
shutdown), instead of then calling shutdown, which exits, we call
reset.

I'm saying, semantically, if you call 'qemu_shutdown_requested()', if it returns 1, it means, immediately shutdown the VM--regardless of where it's called.

The semantics of qemu_reboot_requested() are, if it returns 1, then only when you see an ACPI soft power off, reset the VM. It's that difference in semantics that I think could lead to confusion.

Also, the soft reset flag ought to get reset whenever a VM changes it's state. That is, if you do a system_reboot, then a system_reset (imagine that the reboot fails), then you do a normal powerdown in the guest, instead of shutting off like the user would expect, we'll reboot because the qemu_reboot_requested() is still true.

A good way to do that would be by registering a reset handler in hw/acpi.c. In fact, I think that the whole functionality probably should live in hw/acpi.c.

OK

And I think this also needs to be stored as part of the savevm state for hw/acpi.c. If you do a system_reboot followed by an immediate live migration, without the savevm handler, the VM will shutdown completely after the migration instead of rebooting as expected.

Would it? I don't see that we are saving powerdown|shutdown|reset
request flags?  Sounds like all of those flags need to be in the save
state, and separate patch IMHO.

No, they don't.

A qemu_powerdown_request() call happens from the monitor. This is to allow a graceful shutdown (as opposed to exiting from the monitor). This will trigger the TCG loop to immediately exit. The state doesn't need to be saved because you cannot do a migration in between when qemu_powerdown_request() is called and when the shutdown actually happens.

--
Regards,

Anthony Liguori





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