Re: [PATCH 6/8] libxl: Allow local access for block devices with hotplug scripts

[Ian Jackson <Ian.Jackson@eu.citrix.com>]

George Dunlap writes ("[PATCH 6/8] libxl: Allow local access for block devices with hotplug scripts"):
> pygrub and qemuu need to be able to access a VM's disks locally in
> order to be able to pull out the kernel and provide emulated disk
> access, respectively.  This can be done either by accessing the local
> disk directly, or by plugging the target disk into dom0 to allow
> access.

Some long lines, `if(', etc., in this patch, I'm afraid.

> Unfortunately, while the plugging machinery works for pygrub, it does
> not yet work for qemuu; meaning that disk hotplug scripts cannot be
> used with HVM domains.
> 
> Fortunately, disks using hotplug scripts created in dom0 do create a
> block device as part of set-up, which can be accessed locally; and if
> they use block-common.sh:write_dev, this path will bre written to
> physical-device-path.
> 
> Modify libxl__device_disk_setdefault() to be able to fish this path
> out of xenstore and pass it back.
> 
> We need the target domid to find the appropriate xenstore node, so add
> that to libxl__disk_local_state.

I couldn't find that change in this patch.

> +    /* 
> +     * If the format isn't raw and / or we're using a script, then see
> +     * if the script has written a path to the "cooked" node
> +     */
> +    if(disk->script && domid != INVALID_DOMID) {
> +        libxl__device device;
> +        char *be_path, *pdpath;
> +        int rc;

I don't see where you check that the disk is not being provided by a
driver domain - in which case the hotplug script ran in the driver
domain and the device path is also only in the driver domain.

(By `driver domain' I mean, really, a domain other than this one.)

>  _hidden char * libxl__device_disk_find_local_path(libxl__gc *gc, 
> +                                                  libxl_domid domid,

This new parameter would maybe be a little less confusing if it were
explicitly `guest_domid'; after all it might be the driver domain
domid.

Thanks,
Ian.

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