Re: [Xen-devel] [PATCH] build: save generated config in /boot

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.01.16 at 13:17, <wei.liu2@xxxxxxxxxx> wrote:
> On Wed, Jan 06, 2016 at 03:38:36AM -0700, Jan Beulich wrote:
>> >>> On 06.01.16 at 11:31, <ian.campbell@xxxxxxxxxx> wrote:
>> > On Wed, 2016-01-06 at 02:22 -0700, Jan Beulich wrote:
>> >> > > > On 05.01.16 at 17:53, <cardoe@xxxxxxxxxx> wrote:
>> >> > On 12/22/15 10:09 AM, Jan Beulich wrote:
>> >> > > > > > On 22.12.15 at 17:02, <cardoe@xxxxxxxxxx> wrote:
>> >> > > > How does it not make sense in this case? That's what Andrew and I
>> >> > > > are
>> >> > > > asking you to explain.
>> >> > > 
>> >> > > But I already explained it: The file isn't needed for booting.
>> >> > 
>> >> > One use of it in /boot would be to check the file in 20_linux_xen like
>> >> > we check the kernel config for different options to add different
>> >> > parameters.
>> >> 
>> >> Which, if you search for it, is a very controversial thing: I agree
>> >> with the side demanding for grub to not inspect the kernel's
>> >> .config.
>> > 
>> > What is the preferred mechanism for determining from the contents of /boot
>> > whether an XSM entry should be produced or not?
>> 
>> I don't think this can be inferred - iirc even an XSM-enabled build
>> can be booted without unless in some kind of strict mode? IOW
>> this needs to be configured on the host, not guessed by
>> inspecting .config. (And as a side note, inspecting .config doesn't
> 
> It's better to lower the hurdle for XSM adoption by instructing grub to
> do sensible default than requiring users to produce entries by hand,
> isn't it?
> 
>> truly require .config to be on the boot partition, unless such
>> inspection would happen at boot time, which I don't think is the
>> case.)
>> 
> 
> Yes and no.
> 
> It's true that it can be placed anywhere on the file system as long as
> grub (or any other tools that need to inspect it) can find it.
> 
> But how would you propose grub to deal with this? The location needs to
> be "fixed" from then on and present forever. Either we need to persuade
> every distro to accept our new less-well-known location to always place
> .config there or we make them patch grub as they package Xen. This is
> just unnecessary work.  Anywhere other than /boot is inferior IMHO.

I think we need to separate the two issues: First we need to
settle on whether inspecting .config for XSM purposes is (a)
necessary and if so (b) the right approach (which I doubt).
See also my other reply to Ian sent a minute or two ago. Only
then do we need to get concerned about whether .config
really has a use when placed on /boot.

Jan


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