Re: xm list d flag?

[Anthony Liguori <aliguori@us.ibm.com>]

Christian Limpach wrote:

>>Is changing the order of token and path really necessary?  It's a 
>>considerably simplier change if we maintain the same order.  I've always 
>>thought of the token as an argument so this order makes more sense to me 
>>(and I reckon to Rusty since he did it this way to begin with :-)).
>>    
>>
>
>It's not absolutely necessary, but makes the code simpler sinceat least
>within the kernel, we don't pass the token to the watch callback, only
>the path and as pointed out in a footnote, you can then get the additional
>arguments by adding strlen(path)+1 and so on.
>  
>
So you want to just pass around the path pointer?  And rely on people 
jumping past the end of the string?  Yikes :-)

>>The only adjustment to the userspace API would be that instead of 
>>returning an char *[2] we would return a char *[] that was terminated by 
>>a NULL.  xenbus needs a little more but it's not too bad.
>>    
>>
>
>Wasn't there a patch which got rid of that array?
>
I sent a patch that added a size to the array--Rusty didn't like it.  
Rusty suggested changing the userspace interface to something similiar 
to the kernel interface.

The kernel interface doesn't generalize well--we could hack it to have 
an additional domid_t * parameter but that kind of sucks.

>  Also, with a
>variable number of paths, using an array will become quite complicated
>since you won't know how big to allocate the array.
>  
>
I was thinking of just adding a param to the message that specified the 
number of entries in the array.  That solves that problem.

>Also, I'd like to see something like XS_WATCH_TOKEN and XS_WATCH_PATH
>as indexes into the array instead of sprinking 0/1 althrough the code,
>whether we reverse the order or not...
>  
>
Yes, I had thought of this myself.  I think having xs_read_watch return 
the size of the array is the best solution.  Returning a zero-terminated 
array makes it difficult to determine if the watch has a feature (if you 
know the size, you can check for size < XS_WATCH_* to determine if the 
watch has a given parameter).

I'm going to working something up and submit it.  Rusty can weigh in 
when he gets to Cambridge.

Regards,

Anthony Liguori

>    christian
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