Hi Keir,
I am sorry for the delayed response. 
This is the patch reflecting yourI'd like to post the patch 
that reflects your advice in the mail below.
http://lists.xensource.com/archives/html/xen-devel/2006-07/msg00307.html
It becomes possible to put Xen console message into syslog 
and to know the time stamp. 
> Yes, that is an out-of-range input index gets 'rounded up' to the first 
> in-range index. I think that seems a sensible method for bootstrapping 
> a caller with no knowledge about current ring indexes -- they'd pass 
> zero as input and then get back information about the first valid 
> index. Another way would be to have an input flag or unique input index 
> value that means 'just get me characters from the first valid index'. I 
> somewhat prefer the method I already described though.
You are right. 
If the index that specified by the caller program is older than 
the oldest readable character index, Xen returns the current oldest index 
in this patch.
The policy of the change is as follows. 
1. The existing library interface is not changed 
 except "xen_sysctl_readconsole" structure. 
2. A new library interface is designed to hand over the index managed by
 the program that reads console messages. 
3. "xen_sysctl_readconsole" structure is changed as follows: 
 - The type of "clear" menber is moved to int32_t.
 - "cindex" member is added.
Signed-off-by: Katsuhito Minai <minai@xxxxxxxxxxxxxx>
Best Regards,
Katsuhito Minai
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