Xen devel - Jul 2006 - [PATCH] xenmon: remove magic number "31" (the idle domain)

Hi,

This patch removes the magic number "31" for readability. The number
"31" means the idle domain ID.

In detail:
- display the idle domain ID with "Idle" instead of "31" 
- write to the file "log-idle.log" instead of
"log-dom31.log".

Signed-off-by: KUWAMURA Shin''ya <kuwa@jp.fujitsu.com>

Thanks,
-- 
  KUWAMURA Shin''ya


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On 4 Jul 2006, at 06:37, KUWAMURA Shin''ya wrote:
> This patch removes the magic number "31" for readability. The
number
> "31" means the idle domain ID.
>
> In detail:
> - display the idle domain ID with "Idle" instead of
"31"
> - write to the file "log-idle.log" instead of
"log-dom31.log".
>
> Signed-off-by: KUWAMURA Shin''ya <kuwa@jp.fujitsu.com>
Where does the magic number ''31'' come from in the first place?
That''s
not the number Xen uses. It could conflict with the domain id of a 
non-idle domain.

  -- Keir


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Hi Keir,
>>>>> On Tue, 4 Jul 2006 08:06:57 +0100
>>>>> Keir.Fraser@cl.cam.ac.uk(Keir Fraser)  said:
> 
> 
> On 4 Jul 2006, at 06:37, KUWAMURA Shin''ya wrote:
> 
> > This patch removes the magic number "31" for readability.
The number
> > "31" means the idle domain ID.
> 
> Where does the magic number ''31'' come from in the first
place? That''s
> not the number Xen uses. It could conflict with the domain id of a 
> non-idle domain.
"31" comes from xenmon.py and xenbaked.h.
xenmon.py:38:
  NDOMAINS = 32

xenbaked.h:42
  #define NDOMAINS 32

Notice that 31 is NDOMAINS-1.

Therefore, xenmon supports only up to 32 domains.

Thanks,
-- 
  KUWAMURA Shin''ya

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On 4 Jul 2006, at 08:48, KUWAMURA Shin''ya wrote:
>> Where does the magic number ''31'' come from in the
first place? That''s
>> not the number Xen uses. It could conflict with the domain id of a
>> non-idle domain.
>
> "31" comes from xenmon.py and xenbaked.h.
> xenmon.py:38:
>   NDOMAINS = 32
>
> xenbaked.h:42
>   #define NDOMAINS 32
>
> Notice that 31 is NDOMAINS-1.
>
> Therefore, xenmon supports only up to 32 domains.
That''s poor, since it in fact only really supports the first 31 domains
created on a system (domain ids don''t necessarily quickly get reused; 
and 32nd domid is used as sentinel to indicate idle). It shouldn''t be 
hard to use a data structure more complicated than (presumably) a small 
array indexed by domid.

  -- Keir


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Keir Fraser wrote:
>> Therefore, xenmon supports only up to 32 domains.
>
> That''s poor, since it in fact only really supports the first 31 
> domains created on a system (domain ids don''t necessarily quickly
get
> reused; and 32nd domid is used as sentinel to indicate idle). It 
> shouldn''t be hard to use a data structure more complicated than 
> (presumably) a small array indexed by domid. 
I know about this problem. I''ve got a fix for it I prepared some time 
ago but never got around to submitting. I''ll integrate it with the 
latest source and get it sent out this week.

Rob



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