[U-Boot-Users] RFA & Update: Using libfdt in u-boot for fdt command

Jerry Van Baren
2007-03-02T12:31:39Z

David Gibson wrote:
> On Fri, Mar 02, 2007 at 12:25:17AM -0500, Jerry Van Baren wrote:
>> David Gibson wrote:
>>> On Thu, Mar 01, 2007 at 11:08:38PM -0500, Jerry Van Baren wrote:
>> [snip]
>>
>>>> to give me a pointer to the node name for node tags and property name
>>>> for property tags. Now that I have it working, it would be trivial to
>>>> change the calls to _fdt_next_tag() to instead call fdt_next_tag()
>>>> passing NULL for the new fourth parameter **namep. ;-)
>>>>
>>>> The reason I need it, I'm printing an unknown tree by stepping through
>>>> the tree discovering the node and property names. I need to have
>>>> fdt_next_tag() return the *name* of the node/property as well as the tag
>>>> so that I can print and indent for nodes or look up the property value
>>>> and print the name=value combination.
>>> Hrm. And it returns NULL for tags without a name?
>> I was unable to generate a tag without a name using dtc (other than the
>> root node). It should/would return null, which would be a problem. :-/
>
> I was thinking more of tag types which don't have a name, to wit,
> FDT_END_NODE and FDT_NOP.
>
>>> That might be a useful extension for the next_tag function. The one
>>> thing I'm concerned about is who's responsible for verifying the name
>>> pointer. I'm trying to keep libfdt robust enough that evern if
>>> presented with a badly corrupt blob it will fail relatively
>>> gracefully. Ideally, no matter what it's presented with, it will
>>> always return at worst FDT_ERR_BADSTRUCTURE rather than crashing and
>>> will under no circumstances access memory outside the given blob
>>> size.
>> [snip]
>>
>>>> Oh gaak! What I hear you saying... if you have node a with subnode b
>>>> and property b, subnode b has a property c:
>>>> /a => node
>>>> /a/b => node
>>>> /a/b => property (inside node a)
>>>> /a/b/c => property (inside node b)
>>> Well, yes. Except that in OF and derived terminology, properties are
>>> *never* referred to by path in this way. It's always:
>>> "property 'fred' of node /foo/bar/baz"
>> I'm coming from a human interface syntax point of view and assumed that
>> the human interface is paths like linux where the last item is a
>> directory or file with the computer guessing what you really meant
>> (which _isn't_ ambiguous in file/dir paths). Is there a better syntax
>> for distinguishing between node paths and properties?
>
> You assumed incorrectly. Well, unless you count /proc/device-tree as
> a human interface to the device tree, which isn't entirely
> unreasonable. OF certainly doesn't use that approach, it uses state
> instead, first "dev /foo/bar/baz" then ".properties" or "setprop ....".

OF is a programming language that has some crude elements of interaction
(wouldn't that be "/foo/bar/baz" dev in Forthspeak? ;-). Making user
interface commands have state, where you do "fdt dev /foo/bar/baz"
(remembering the offset of the node) and then "fdt .properties"
implicitly working on /foo/bar/baz is ugly ugly ugly.

We need a usable human interface syntax, replacing the last "/" with
some other character that is not a legal character for a name and thus
won't cause confusion. I am not familiar enough with OF to know if
there is a unique character that can be used for the node path vs.
property separator. If someone has a good one, hollar, otherwise I'll
do some more research when I have time.

Lacking a good property separator character, I will be sticking with the
convention that the stuff after the last "/" is a node unless that
assumption is wrong, in which case it is a property.

Best regards,
gvb