Re: [Qemu-devel] [PATCH] Flush pending AIO on reboot and shutdown.

[Gleb Natapov <gleb@qumranet.com>]

On Wed, Aug 13, 2008 at 03:06:41PM +0100, Samuel Thibault wrote:
> Gleb Natapov, le Wed 13 Aug 2008 16:59:41 +0300, a écrit :
> > On Wed, Aug 13, 2008 at 02:46:08PM +0100, Samuel Thibault wrote:
> > > Gleb Natapov, le Wed 13 Aug 2008 16:23:58 +0300, a écrit :
> > > > If there is outstanding IDE IO when BIOS starts execution then IDE
> > > > commands sent by BIOS will interfere with it and will leave IDE
> > > > subsystem in unpredictable state. This can happen when system reboots
> > > > unexpectedly without waiting for IO completion. Flushing IO before exit
> > > > prevents data lose.
> > > 
> > > I'm wondering: isn't that what happens with real machines?
> > > 
> > With shutdown yes, but why not try harder. With reboot I don't think
> > that in real HW you can hang IDE interface after reboot ;)
> 
> Mmm, I couldn't understand.
> 
> With real hardware, if you reboot into the bios the board is not
> resetted either, and thus the interference is the same.
> 
On real hardware if you press reset button then HW reset is performed
(not power up reset) and qemu HW handles this in reset notifiers. I have
no idea what IDE does during reset with outstanding IO. It should either
cancel it or complete it. Currently BOCHS BIOS doesn't check that IDE is
busy (it doesn't even know that HW is present) and sends overlapping
command.

--
			Gleb.