Re: [Xen-devel] [PATCH] Add an ioctl interface for simple xenstore access

[Ewan Mellor <ewan@xxxxxxxxxxxxx>]

On Mon, Mar 20, 2006 at 09:38:22AM +0100, Gerd Hoffmann wrote:

> > We had discussed this in a previous thread and I thought you were okay
> > with this approach.  The /proc/xen/xenbus interface requires full
> > parsing of the XenBus protocol.  This requires libxenstore in domU. 
> > Today, libxenstore is shipped with the rest of the tools package on most
> > distros.  
> 
> Changing this and move libxenstore to another package (to avoid pulling
> in xend with python if everything you want is xenstore access) isn't a
> big problem ...
> 
> btw: are xenstore watches supposed to work inside domU?

Watches work in kernel space in domU (the frontends to the split device
drivers use them), but they don't work in userspace there.  The problem is
that there is no support in xenbus for blocking a userspace process waiting
for a watch to fire.

In domain 0, Xend uses a unix domain socket straight to Xenstored: it can
block on that, as it's not going through the Xenbus kernel-level driver.

If someone wanted to add such support, that would be appreciated.

Ewan.

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