Re: [PATCH] Don't attach needless options when launch pygrub

[Zhigang Wang <zhigang.x.wang@oracle.com>]

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On 07/14/2010 04:10 PM, Ian Campbell wrote:
> On Wed, 2010-07-14 at 08:29 +0100, Yu Zhiguo wrote:
>> Hi Ian,
>>
>> Ian Campbell wrote:
>>> On Wed, 2010-07-14 at 07:15 +0100, Yu Zhiguo wrote:
>>>> We should always run grub if bootloader is specified,
>>>> options 'kernel' and 'ramdisk' are needless.
>>>
>>> Not quite. If you specify both bootloader and kernel then this instructs
>>> pygrub to extract the specific named file from the guest file system,
>>> similarly for the ramdisk.
>>>
>>
>>  Do you mean in this case, pygrub will use specified kernel
>> that lie in the filesystem of the DomU?
> 
> I thought so, I looks like I was mistaken though.
> 
>>  I think this is good. But now pygrub's action is using the
>> specified kernel in Dom0, but not run grub.
> 
> Hmm, pygrub is certainly run, regardless of having a kernel configured
> or not. What is in question is what --kernel and --ramdisk actually
> cause pygrub to do and whether that is useful.
> 
> As far as I can see the --kernel and --ramdisk options end up in the
> incfg map which only used in a handful of places, most of which just
> extract incfg["args"]. The only places which do not do this are the
> calls to sniff_solaris and sniff_netware both of which appear to make
> use of incfg["kernel"] (but not incfg["ramdisk"]).
> 
> So it looks like specifying the kernel option in addition to bootloader
> is infact useful if you are booting a Solaris or Netware domU but is
> harmless/ignored otherwise. I think we need to continue to support this
> use case and I don't see any particular reason to force those users to
> change their configuration file syntax for this issue (if it's even an
> issue, I still don't really see the problem).
> 
> Perhaps it would be better to update pygrub so that --kernel actually
> does something consistent in the non-{Solaris,Netware} case, such as
> perhaps selecting the configuration entry with the match kernel path
> instead of defaulting to entry 0? (e.g. make "-q --kernel=/boot/FOO"
> select the entry with kernel /boot/FOO)
> 
> It looks like --ramdisk (and the associated plumbing through xend) may
> in fact be useless at this time. I'd say it is harmless to plumb it
> through for consistency though -- perhaps in the future pygrub (or
> another bootloader) might want to use it.
> 

Yes. Please don't remove --kernel/--ramdisk: pygrub is not the only pv guest
bootloader.

Here is a pv guest boot loader we are using which grab vmlinuz/initrd from
network. It uses --kernle/--ramdisk parameters.

Thanks,

Zhigang

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