On 05.10.2012, at 02:34, David Gibson wrote: > On Thu, Oct 04, 2012 at 04:25:28PM +0530, Avik Sil wrote: >> On 09/27/2012 03:21 PM, Gleb Natapov wrote: >>> On Thu, Sep 27, 2012 at 11:33:31AM +0200, Alexander Graf wrote: >>>> >>>> On 27.09.2012, at 11:29, Benjamin Herrenschmidt wrote: >>>> >>>>> On Thu, 2012-09-27 at 14:51 +0530, Avik Sil wrote: >>>>>> Hi, >>>>>> >>>>>> We would like to get a method to boot from devices provided in -boot >>>>>> arguments in qemu when the 'boot-device' is set in nvram for pseries >>>>>> machine. I mean the boot device specified in -boot should get a >>>>>> precedence over the 'boot-device' specified in nvram. >>>>>> >>>>>> At the same time, when -boot is not provided, i.e., the default boot >>>>>> order "cad" is present, the device specified in nvram 'boot-device' >>>>>> should get precedence if it is set. >>>>>> >>>>>> What should be the elegant way to implement this requirement? >>>>>> Suggestions welcome. >>>>> >>>>> Actually I think it's a more open question. We have essentially two >>>>> things at play here: >>>>> >>>>> - With the new nvram model, the firmware can store a boot device >>>>> reference in it, which is standard OF practice, and in fact the various >>>>> distro installers are going to do just that >>>>> >>>>> - Qemu has its own boot order thingy via -boot, which we loosely >>>>> translate as c = first bootable disk we find (actually first disk we >>>>> find, we should probably make the algorithm a bit smarter), d = first >>>>> cdrom we find, n = network , ... We pass that selection (boot list) down >>>>> to SLOF via a device-tree property. >>>>> >>>>> The question is thus what precedence should we give them. I was >>>>> initially thinking that an explicit qemu boot list should override the >>>>> firmware nvram setting but I'm now not that sure anymore. >>>>> >>>>> The -boot list is at best a "blurry" indication of what type of device >>>>> the user wants ... The firmware setting in nvram is precise. >>>> >>>> IIRC gleb had implemented a specific boot order thing. Gleb, mind to >>>> enlighten us? :) >>>> >>> Yes, forget about -boot. It is deprecated :) You should use bootindex >>> (device property) to set boot priority. It constructs OF device path >>> and passes it to firmware. There is nothing "blurry" about OF device >>> path. The problem is that it works reasonably well with legacy BIOS >>> since it is enough to specify device to boot from, but with EFI (OF is >>> the same I guess) it is not enough to point to a device to boot from, >>> but you also need to specify a file you want to boot and this is where >>> bootindex approach fails. If EFI would specify default file to boot from >>> firmware could have used it, but EFI specifies it only for removable media >>> (what media is not removable this days, especially with virtualization?). >>> We can add qemu parameter to specify file to boot, but how users should >>> know the name of the file? >>> >> I looked at the bootindex stuff and found that when the bootindex is >> specified for the disk and cdrom it generates a string like: >> >> "/spapr-vio-bridge/spapr-vscsi/channel@0/disk@0,1 >> /spapr-vio-bridge/spapr-vscsi/channel@0/disk@0,0" > > Ok, so I've just started looking at the bootindex stuff. What > function is generating these strings? > > We should also be able to get the raw bootindex values for a qdev, > yes? I was thinking we could instead copy those values into the > device tree when we populate it. The trouble is that we don't > actually generate (in qemu) nodes for individual disks under a vscsi, > or for individual PCI devices under the host bridge (that's done by > SLOF). Still thinking...
Well. You can track it down to the device level and you know the drive index. Maybe you could be clever if you had a device property that contains the drive index and boot index to it? > > An aside, I'm thinking that once we do get bootindex working, then > boot devices specified in NVRAM should have priority below all devices > with explicit supplied bootindex, but above any that don't. Does that > seem right to you? Yes, that sounds exactly right :). > >> Now converting/translating this to OF device path is going to be >> much trickier and might not be proper. So I propose a simple >> solution by introducing a global flag that checks if explicit -boot >> parameter is provided or not. The presence of this parameter is >> verified in SLOF firmware. The flag had to be introduced as >> boot_devices defaults to "cad" instead of null and passed to >> machine->init(). > > So, personally, I think this is quite a reasonable interim measure > until we figure out how to do bootindex. I will fold it into our > internal tree for now, even if the qemu people are going to bitch and > moan about its imperfections. Can you send me a clean copy with > commit message, please? I actually don't remember having seen a patch at all :). Alex