Re: [Xen-devel] [RFC] KEXEC: Clean up logic to choose a range for the crash kernel

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 25/11/11 17:03, Andrew Cooper wrote:
>
> On 25/11/11 16:49, Jan Beulich wrote:
>>>>> On 25.11.11 at 17:03, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>>> On 25/11/11 15:36, Jan Beulich wrote:
>>>>>>> On 25.11.11 at 16:12, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>>>> Where's that happening? Are you perhaps mis-interpreting the
>>>> purpose of these ranges?
>>> I might possibly be misinterpreting these ranges as the only
>>> documentation is the code, but I believe I have got it correct based on
>>> the upstream Linux code.  What are your interpretations of the ranges?
>> The ranges are to say "if the system has between <start> and <end>
>> amount of memory, then allocate a <size> block (possibly located at
>> <offset>).
> Ah ok.  That actually makes more logical sense.  Is there some
> documentation as to exactly what is permitted to specify? I have not
> been able to find any.
>
>>>>> 4) Remove the kexec reservation code when considering modules
>>>>>     This code only had any effect for people using the "newer" syntax
>>>>>     on the command line, as people using the "classic" syntax would
>>>>>     reserve a memory region before considering modules.
>>>> Are you sure? How do you prevent the kexec area from overlapping
>>>> any of the modules (in particular the initrd, which can get passed in
>>>> place to Dom0)?
>>> Good point, which is why this is an RFC.  Note that the "classic"
>>> syntax, which everyone refers to in documents on the subject, will never
>>> consider any of the modules.
>> It won't in either case when addresses are specified. It will in
>> both cases when only sizes are provided.
> How can you specify an offset while using the range syntax?  This leaves
> the classic syntax as the only way to specific an exact location in memory.
>
>>> I am not really sure which is best, but I
>>> would consider positioning the kdump kernel more important than the
>>> location of initrd.  The user is likely to know more about why their
>>> kdump kernel needs to be located where specified than Xen does.  Perhaps
>>> after deciding where the kdump kernel should go, we should move any
>>> overlapping modules?
>> And that's already happening (or is at least supposed to be).
>>
>> Jan

After comparing the Xen parsing code with the Linux parsing code, with
the correct idea of what we are trying to do, Xen still lacks the
ability to specify an exact offset using the newer style.  I will
implement this.

-- 
Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com


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