Re: [Xen-devel] [PATCH V1 08/29] xen/dts: Don't add a fake property "name" in the device tree

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 09/09/2013 10:40 AM, Ian Campbell wrote:
> On Mon, 2013-09-09 at 10:30 +0100, Julien Grall wrote:
> > On 09/06/2013 05:28 PM, Ian Campbell wrote:
> > > On Wed, 2013-08-28 at 15:47 +0100, Julien Grall wrote:
> > > > On new Flat Device Tree version, the property "name" may not exist.
> > > > The property is never used in Xen code except to set the field "name" of
> > > > dt_device_node.
> > > >
> > > > For convenience, remove the fake property. It will save space during the
> > > > creation of the dom0 FDT.
> > > Is it worth diverging from the Linux code this is based on over this
> > > though?
> > If we don't diverge, I need to add some logic in device tree creation to
> > know if the "name" property was generated by Xen.
> Because otherwise it gets included in the DTB given to dom0? Is that
> harmful though?
The current device tree creation code is not able to reallocate memory 
if the device tree is bigger than the real one plus a small constant. I 
don't think it's easy to handle it because we don't have realloc 
function in Xen.
> > The others solutions was:
> >      1) Add the logic during device tree creation
> >      2) Add a boolean to know if the property is a fake
> Would it be possible to reduce the divergence, at the cost of a little
> bit of dead code by not actually removing the code which makes up the
> name, but rather short circuiting it with a "continue" or an "if (0
> &&  ...)" (plus an appropriate comment).
I found this solution a bit ugly, but if we can avoid a divergence and 
some logic in device creation... I will rework the patch with this solution.
> > Currently, the "name" property value is replicated in the name field of
> > dt_device_node. Except staying close to Linux code, I don't see a good
> > reason to create this fake property.
> >
> > > > Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> > > > ---
> > > >    xen/common/device_tree.c |   21 +++++++++------------
> > > >    1 file changed, 9 insertions(+), 12 deletions(-)
> > > >
> > > > diff --git a/xen/common/device_tree.c b/xen/common/device_tree.c
> > > > index be592d2..07a19ac 100644
> > > > --- a/xen/common/device_tree.c
> > > > +++ b/xen/common/device_tree.c
> > > > @@ -1543,6 +1543,7 @@ static unsigned long __init unflatten_dt_node(const void 
> > > > *fdt,
> > > >        if ( !has_name )
> > > >        {
> > > >            char *p1 = pathp, *ps = pathp, *pa = NULL;
> > > > +        char *tmp = NULL;
> > > >            int sz;
> > > >
> > > >            while ( *p1 )
> > > > @@ -1556,25 +1557,21 @@ static unsigned long __init unflatten_dt_node(const 
> > > > void *fdt,
> > > >            if ( pa < ps )
> > > >                pa = p1;
> > > >            sz = (pa - ps) + 1;
> > > > -        pp = unflatten_dt_alloc(&mem, sizeof(struct dt_property) + sz,
> > > > -                                __alignof__(struct dt_property));
> > > > +
> > > > +        tmp = unflatten_dt_alloc(&mem, sz, 1);
> > > >            if ( allnextpp )
> > > >            {
> > > > -            pp->name = "name";
> > > > -            pp->length = sz;
> > > > -            pp->value = pp + 1;
> > > > -            *prev_pp = pp;
> > > > -            prev_pp = &pp->next;
> > > > -            memcpy(pp->value, ps, sz - 1);
> > > > -            ((char *)pp->value)[sz - 1] = 0;
> > > > -            dt_dprintk("fixed up name for %s -> %s\n", pathp,
> > > > -                       (char *)pp->value);
> > > > +            memcpy(tmp, ps, sz - 1);
> > > > +            np->name = tmp;
> > > > +            tmp[sz - 1] = 0;
> > > > +            dt_dprintk("fixed up name for %s -> %s\n", pathp, np->name);
> > > >            }
> > > >        }
> > > > +
> > > >        if ( allnextpp )
> > > >        {
> > > >            *prev_pp = NULL;
> > > > -        np->name = dt_get_property(np, "name", NULL);
> > > > +        np->name = (np->name) ? : dt_get_property(np, "name", NULL);
> > > >            np->type = dt_get_property(np, "device_type", NULL);
> > > >
> > > >            if ( !np->name )

--
Julien Grall

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