Alexander Graf <ag...@suse.de> writes: > On 22.09.2012, at 15:31, Blue Swirl <blauwir...@gmail.com> wrote: > >> On Fri, Sep 21, 2012 at 3:08 AM, David Gibson >> <da...@gibson.dropbear.id.au> wrote: >>> Below is a patch which implements the (PAPR mandated) NVRAM for the >>> pseries machine. It raises a couple of generic questions. >>> >>> First, this adds a new "nvram" machine option which is used to give a >>> block device id to back the NVRAM so it is persistent. Since some >>> sort of NVRAM is quite common, it seems this might be useful on other >>> machines one day, although obviously nothing else implements it yet. >> >> Yes, there have been discussions earlier since loading NVRAM contents >> from a file would be useful for many architectures too. >> >>> >>> Second, if a block device is not specified, it simply allocates a >>> block of memory to make a non-persistent NVRAM. Obviously that isn't >>> really "NV", but it's enough to make many guests happy most of the >>> time, and doesn't require setting up an image file and drive. It does >>> mean a different set of code paths in the driver though, and it will >>> need special case handling for savevm (not implemented yet). Is this >>> the right approach, or should I be creating a dummy block device for a >>> one-run NVRAM of this kind? I couldn't see an obvious way to do that, >>> but maybe I'm missing something. >> >> That was the problem earlier too, it looks like a generic way for all >> NVRAM/flash devices should be obvious but so far nobody has been able >> to propose something. >> >> What if there are two devices which could use this, for example CMOS >> and flash on x86? >> >> This should be extending -device syntax rather than adding another >> top level option. Something like >> -drive foo,file=nvram.qcow2,format=qcow2,id=main_nvram -device >> spapr-nvram,drive_id=main_nvram > > Could we create a simplified syntax for this in addition? Something like > > -device spapr-nvram,file=nvram.raw > > which would then automatically spawn a drive for the user. Saving the > machine state would obviously save the transparently created drive.
We can't ask people to rewrite half of QEMU just to merge a feature. In this case, what matters is: 0) The device should always be modelled with QOM/qdev 1) If the device is a fundamental part of the machine (i.e. you can't do anything useful with out it), then it's configuration should be specified as a machine parameter. 2) If !(1), the device should be added with -device 3) Devices deal with backends and only with backends. We have a syntax for specifying backends independently of backends. If you want a single option to configure a device, that's a problem to attempt to solve independent of this series. > But I don't want to force people to have to use -device syntax for the > average qemu use cases. Sorry, but that's where we're at today. -device is part of our user interface. It's a management tool only interface and we cannot replicate every option just because you don't like the syntax. Regards, Anthony Liguori
