[Xen-devel] Block device configuration

[Rusty Russell <rusty@xxxxxxxxxxxxxxx>]

Hi all,

        Am trying to write a skeleton driver, so I'm trying to understand the
store interface for block devices.  Is this correct, and what it's going
to be in 3.0?

Tool (eg. xend) creates two directories (with a single transaction ?):

        <backend>/backend/vbd/<per-frontend-dir>/<device-id>/
                domain: name of frontend domain
                type: "phy" or "file"
                params: path of device (type=phy) or file (type=file)?
                dev: the device the frontend is going to see
                frontend: path of frontend device directory
                frontend-id: domain id of frontend directory.

        <frontend>/device/vbd/<device-id>/
                virtual-device: same as "dev" in backend dir
                backend: path of backend device directory
                backend-id: domain id of backend

Now, under Linux, the following happens on the backend:
        xenbus notices new backend device appear, calls vbd backend
        driver (which places a watch on itself), and invokes hotplug
        script (or udev) in userspace.
        
        hotplug script reads parameters from directory, and writes
        physical-device node.
        
        vbd backend notices creation of physical-device node.  It then
        looks at frontend to "ring-ref" and "event-channel" values, then
        and writes "sectors", "info" and "sector-size".

Under Linux, the following happens on the frontend:
        xenbus notices new device appear, calls vbd frontend driver, and
        invokes hotplug/udev.
        
        driver places watch on backend, reads "virtual-device" and
        creates writes "ring-ref" and "event-channel".  Tries to read
        "sectors", "info" and "sector-size" from backend.

Is this the model the skeleton driver should follow, or are more changes
anticipated?

Rusty.
-- 
A bad analogy is like a leaky screwdriver -- Richard Braakman


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