RE: [Xen-devel] [PATCH][RESEND]Nvram patch for IA64

["Yu, Ke" <ke.yu@xxxxxxxxx>]

Ian Pratt  write on 2006?11?1? 16:25:
>> I am not familiar with the xan-api project, so could you please give
>> more info on "trigger a watcher and store it outside of xenstore"?
> 
> See xenbits.xensource.com/ext/xen-api.hg
> 
> Various parts of a domain's runtime config are persisted in a
> database, and the nvram state could be added to this. There's no good
> example to copy as the nvram state is unusual in that its written by
> both qemu rather than the control tools. Xenbus watchers let you do
> this, though. 
> 
>> Does xenstore
>> has the interface to write data outside of xenstore.
> 
> You can register a watcher to be told when someone writes to a section
> of the store then arrange to persist the data. You can add this to
> xend. 
> 
>> Or do you mean having
>> a separate thread to watch, and the thread will write data outside of
>> xenstore. In this way, qemu should have ringbuffer to pass the data
>> to the thread.
> 
> No extra ring buffer is needed or wanted.
> 
> Ian

Thank you for the info. It is clear to me now. we will update the patch as 
following: 

xenstore:
local= " "
   domain = ""
        x = ""                #  domain id
           nvram            #  nvram dir
               file             #  nvram file path
               data_in       # data index + 64 bytes data, 128 characters, for 
qemu write
               data_out     # data index + 64 bytes data, 128 characters, for 
qemu read

xend register two watches on data_in node and data_out node. 
* qemu write data: qemu write "index+data" to data_in node,  xend data_in watch 
handler will copy the data to persisted file. 
* qemu read data: qemu write index to data_out node; xend data_out watch 
handler copy data from persisted file to data_out node; qemu read data_out node.

Best Regards
Ke

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