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

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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