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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 20 Mar 2006, at 08:52, Ewan Mellor wrote:

> 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.
There's no need for special-case blocking in the kernel. The 
libxenstore reader thread will block on read() and then wake up other 
threads as necessary by writing to a pipe. All that's needed in the 
kernel is some bookkeeping to allow demux and teardown if the device 
file is closed. Some of that can be pushed to xenstored if we extend it 
to support multiple connections over a single shared page, but it's not 
really necessary.
 -- Keir


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