Re: [Xen-devel] xm list d flag?

[Anthony Liguori <aliguori@xxxxxxxxxx>]

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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