Re: [PATCH 1/2] fdt: Allow stacked overlays phandle references

On Thu, Jul 13, 2017 at 08:38:10PM +0100, Phil Elwell wrote:

Can we also consider a mechanism for overlay-local symbols, i.e. symbols
that are used purely to create links within an overlay - perhaps using a
particular naming convention? This would make it easier to instantiate an
overlay multiple times without having to uniquify all symbols, and it would
avoid polluting the global namespace without reason.

I'd really prefer not to add yet more features and complexity to the
existing shoddily designed overlay mechanism.  I'd prefer for people
to focus on a better replacement - which includes considering these
sorts of use cases and how to handle them.

Phil

On 13 Jul 2017 8:32 pm, "Frank Rowand" [off-list ref] wrote:

quoted

On 07/03/17 02:06, David Gibson wrote:

quoted

On Wed, Jun 14, 2017 at 05:52:25PM +0300, Pantelis Antoniou wrote:

quoted

This patch enables an overlay to refer to a previous overlay's
labels by performing a merge of symbol information at application
time.

This seems to be doing things the hard way.

You're essentially extending the semantics of overlay application to
add the symbol merging.  You've implemented these extended semantics
in libfdt, which is all very well, but that's not the only overlay
application implementation.


It seems to me a better approach would be to change dtc's -@
implementation, so that in /plugin/ mode instead of making a global
__symbols__ node, it puts it into the individual fragments.  That way
the existing overlay application semantics will update the __symbols__
node.

If the __symbols__ node was inside a fragment, then the existing
code would add (or update) a __symbols__ node located at the location
pointed to by the fragment's target path, instead of updating the
node /__symbols__.

It makes sense to me to have only one global __symbols__ node instead
of several.

If there is a global __symbols__ node then we have a single name
space for symbols.

If there are multiple __symbols__ nodes spread throughout the tree,
then to me that would imply different name spaces spread throughout
the tree, where namespaces are determined by fragments.  This sounds
confusing to me.  Or if the intent is to have a single name space
then the __symbols__ information would be scattered throughout the
tree instead of located in a single node.

My current patch (under review), targeted for Linux 4.13-rc1, puts
an overlay's __symbols__ node properties into the overlay's
changeset, so they get added when the overlay is loaded and
removed when the overlay is unloaded.

-Frank

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson