[Crash-utility] Adding a new command rbtree

[Dave Anderson]

----- Original Message -----
> At 2012-5-22 23:15, Dave Anderson wrote:
> > Doing it that way really confuses two different "offset" issues that are associated
> > with this command:
> >
> >   (1) the offset of an rb_root or radix_tree_node within a containing
> >       data structure, and
> >   (2) the offset of an rb_node within a containing data structure.
> >
> > And in both cases, forget trying to implement the "the -o is not necessary" and
> > "the -o is only necessary..." optimizations, because it would be almost impossible
> > to do.
> 
> Hello Dave,
> 
> I will list all the situations I was concerning.
> 
> First red-black tree:
> 1. rb_node is embedded in a structure. Address is the address of the
> structure, and -o shows the offset of rb_node to the structure.
> 
> 2. same as 1., but the address is the address of rb_node when using -N
> in command line.
> 
> rb_root was not concering. I will recall the reason. I can get the root
> node from rb_root. And then the offspring of the root node. Then I still
> need a offset that shows the offset of the offspring node to its related
> structure to get the structure's information.
> 
> Then radix tree:
> 3. radix_tree_root's address is specified.
> 
> 4. radix_tree_node's address is specified.
> 
> According to your reply, "-r offset" indicates rb_root and radix_tree_root,

Correct, but only if the rb_root or radix_tree_root are embedded in a
data structure, and the address argument points to the data stucture.
 
> and "-n offset" indicates rb_node and radix_tree_node.

No -- the "-n offset" would only applicable to rb_nodes.
 
radix_tree_node structures data are standalone entities that are allocated
from the "radix_tree_node" slab cache, correct?  When would a radix_tree_node
ever be embedded in a containing data structure?

> And if I use "-r offset", then I need another option to show the offset
> of rb_node. And when using "-n offset" together with an address, which
> can only be one of rb_node's address and address of the structure
> rb_node embedded in, I may need another option to indicate the address's
> type.

The address is either that of an rb_root or radix_tree_root, or the 
address of the containing data structure, in which case it would 
require the "-r offset" option.

> 
> So I think "tree -t type -r offset -n offset -m addr..." is a good
> choice. "-r offset" indicates the rb_root or radix_tree_root's offset,
> and "-n offset" indicates the rb_node or radix_tree_node's offset. 

Again, what is a "radix_tree_node offset"?  

> only using "-n offset" indicates the addr is related to rb_node or
> radix_tree_node, but if "-r offset" is also specified, the addr is
> related to rb_root or radix_tree_root. When "-m" is specified, the addr
> is the address of the root(when specified "-r offset") or the node.  If
> "-m" is not specified, the addr is the address of the structure that
> containing the root(when specified "-r offset") or the node.
> 
> Do you think it's OK?

No, that confuses the hell out me...

I really don't understand the need for the additional "-m" option?

To me it's simple -- but I may be missing something.  The address argument
can be either:

 (1) A pointer to an rb_root or radix_tree_root. 
     The "-r offset" is not required.

 (2) A pointer to a data structure containing an rb_root or radix_tree_root.
     The "-r offset" option is required if the member offset is non-zero.
      
That being the case, this should work:

 red-black tree:  tree -t type [-r offset] [-n offset] address
     radix tree:  tree -t type [-r offset] address

In the case of a red-black tree, it seems that you are also trying to
support the bypassing of the rb_root entirely, and point to an rb_node
directly?  That would seem to be an odd-ball case, because the list 
would be truncated if you don't point to the topmost rb_node.  Is that
what you have in mind?  If so, I suppose that you could also have a
additional "-N" option or something like that to signal that the address
argument is a pointer to an rb_node (and not applicable to radix trees). 
 
Dave