Re: [Xen-devel] [PATCH 5/6] libxl: introduce libxl__alloc_vdev

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 27 Mar 2012, Ian Campbell wrote:
> > +static char * libxl__alloc_vdev(libxl__gc *gc, uint32_t domid, 
> > xs_transaction_t t,
> > +        libxl_device_disk *disk)
> > +{
> > +    int rc = 0;
> > +    libxl_device_disk *disks = NULL;
> > +    int num = 0, idx = -1, max_idx = -1, i = 0;
> > +
> > +    rc = libxl__append_disk_list_of_type(gc, domid, t, "vbd", &disks, 
> > &num);
> > +    if (rc) goto out;
> > +
> > +    rc = libxl__append_disk_list_of_type(gc, domid, t, "tap", &disks, 
> > &num);
> > +    if (rc) goto out;
> > +
> > +    rc = libxl__append_disk_list_of_type(gc, domid, t, "qdisk", &disks, 
> > &num);
> > +    if (rc) goto out;
> 
> This is basically an open-coded version of libxl_disk_list, isn't it?

yes it is similar, but as you can see the "smart" bit is in
libxl__append_disk_list_of_type anyway


> For this use though wouldn't it be as easy to simply iterate over idx
> checking if a frontend dir exists?

We could try one at a time: 

xvd(a + idx) -> dev_number -> xs_read * 3

this could work, even though we would still need to read 3 possible
paths (tap, qdisk, vbd) for each one.
It would be more efficient than calling libxl__append_disk_list_of_type
three times, but is it actually simpler?

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