Re: [Xen-users] Got permission denied error when calling xenbus_printf function in the frontend driver

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Tue, 2015-08-04 at 07:07 -0400, Jintack Lim wrote:
> After I added a few lines to give read/write permission of some keys to 
> domU,
> then "permission denied" error was gone, and the driver worked fine.

Great!

> They look like this.
> 
> xenstore-chmod /local/domain/${2}/device/${1}/0/state b
> xenstore-chmod /local/domain/${2}/device/${1}/0/ring-ref b
> xenstore-chmod /local/domain/${2}/device/${1}/0/event-channel b

I think that has likely given r/w access to all domains, probably OK if you
are just benchmarking but don't deploy this :-)

"n${2} r0" AKA owned by the frontend, read-only for the backend (hardcoded
as dom0 here) might be more appropriate in real life.

> /* then fire up the frontend driver */
> 
> >  
> > What is creating /local/domain/<domid>/device/vsimple/<devid> and
> > /local/domain/<be>/backend/vsimple/<domid>/<devid>?
>  
> They are created by the script on dom0.
> As far as I know, 
>  /local/domain/<domid>/device/vsimple/<devid> is automatically created 
> when creating
>  /local/domain/<domid>/device/vsimple/<devid>/backend-id in the script.
> 
> I think the other one is also automatically created when creating 
> frontend-id in the script.

Correct, writing a key creates any intervening "directories". I believe
they inherit there permissions from their parent at the time of creation.

Ian.

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