scripts/gdb: add rb tree iterating utilities

Implement gdb functions for rb_first(), rb_last(), rb_next(), and
rb_prev().  These can be useful to iterate through the kernel's
red-black trees.

[swboyd@chromium.org: v2]
  Link: http://lkml.kernel.org/r/20190329220844.38234-4-swboyd@chromium.org
Link: http://lkml.kernel.org/r/20190325184522.260535-4-swboyd@chromium.orgSigned-off-by: Stephen Boyd <swboyd@chromium.org>
Cc: Douglas Anderson <dianders@chromium.org>
Cc: Nikolay Borisov <n.borisov.lkml@gmail.com>
Cc: Kieran Bingham <kbingham@kernel.org>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Jackie Liu <liuyun01@kylinos.cn>
Cc: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/gdb/linux/rbtree.py

+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright 2019 Google LLC.
+
+import gdb
+
+from linux import utils
+
+rb_root_type = utils.CachedType("struct rb_root")
+rb_node_type = utils.CachedType("struct rb_node")
+
+
+def rb_first(root):
+    if root.type == rb_root_type.get_type():
+        node = node.address.cast(rb_root_type.get_type().pointer())
+    elif root.type != rb_root_type.get_type().pointer():
+        raise gdb.GdbError("Must be struct rb_root not {}".format(root.type))
+
+    node = root['rb_node']
+    if node is 0:
+        return None
+
+    while node['rb_left']:
+        node = node['rb_left']
+
+    return node
+
+
+def rb_last(root):
+    if root.type == rb_root_type.get_type():
+        node = node.address.cast(rb_root_type.get_type().pointer())
+    elif root.type != rb_root_type.get_type().pointer():
+        raise gdb.GdbError("Must be struct rb_root not {}".format(root.type))
+
+    node = root['rb_node']
+    if node is 0:
+        return None
+
+    while node['rb_right']:
+        node = node['rb_right']
+
+    return node
+
+
+def rb_parent(node):
+    parent = gdb.Value(node['__rb_parent_color'] & ~3)
+    return parent.cast(rb_node_type.get_type().pointer())
+
+
+def rb_empty_node(node):
+    return node['__rb_parent_color'] == node.address
+
+
+def rb_next(node):
+    if node.type == rb_node_type.get_type():
+        node = node.address.cast(rb_node_type.get_type().pointer())
+    elif node.type != rb_node_type.get_type().pointer():
+        raise gdb.GdbError("Must be struct rb_node not {}".format(node.type))
+
+    if rb_empty_node(node):
+        return None
+
+    if node['rb_right']:
+        node = node['rb_right']
+        while node['rb_left']:
+            node = node['rb_left']
+        return node
+
+    parent = rb_parent(node)
+    while parent and node == parent['rb_right']:
+            node = parent
+            parent = rb_parent(node)
+
+    return parent
+
+
+def rb_prev(node):
+    if node.type == rb_node_type.get_type():
+        node = node.address.cast(rb_node_type.get_type().pointer())
+    elif node.type != rb_node_type.get_type().pointer():
+        raise gdb.GdbError("Must be struct rb_node not {}".format(node.type))
+
+    if rb_empty_node(node):
+        return None
+
+    if node['rb_left']:
+        node = node['rb_left']
+        while node['rb_right']:
+            node = node['rb_right']
+        return node.dereference()
+
+    parent = rb_parent(node)
+    while parent and node == parent['rb_left'].dereference():
+            node = parent
+            parent = rb_parent(node)
+
+    return parent
+
+
+class LxRbFirst(gdb.Function):
+    """Lookup and return a node from an RBTree
+
+$lx_rb_first(root): Return the node at the given index.
+If index is omitted, the root node is dereferenced and returned."""
+
+    def __init__(self):
+        super(LxRbFirst, self).__init__("lx_rb_first")
+
+    def invoke(self, root):
+        result = rb_first(root)
+        if result is None:
+            raise gdb.GdbError("No entry in tree")
+
+        return result
+
+
+LxRbFirst()
+
+
+class LxRbLast(gdb.Function):
+    """Lookup and return a node from an RBTree.
+
+$lx_rb_last(root): Return the node at the given index.
+If index is omitted, the root node is dereferenced and returned."""
+
+    def __init__(self):
+        super(LxRbLast, self).__init__("lx_rb_last")
+
+    def invoke(self, root):
+        result = rb_last(root)
+        if result is None:
+            raise gdb.GdbError("No entry in tree")
+
+        return result
+
+
+LxRbLast()
+
+
+class LxRbNext(gdb.Function):
+    """Lookup and return a node from an RBTree.
+
+$lx_rb_next(node): Return the node at the given index.
+If index is omitted, the root node is dereferenced and returned."""
+
+    def __init__(self):
+        super(LxRbNext, self).__init__("lx_rb_next")
+
+    def invoke(self, node):
+        result = rb_next(node)
+        if result is None:
+            raise gdb.GdbError("No entry in tree")
+
+        return result
+
+
+LxRbNext()
+
+
+class LxRbPrev(gdb.Function):
+    """Lookup and return a node from an RBTree.
+
+$lx_rb_prev(node): Return the node at the given index.
+If index is omitted, the root node is dereferenced and returned."""
+
+    def __init__(self):
+        super(LxRbPrev, self).__init__("lx_rb_prev")
+
+    def invoke(self, node):
+        result = rb_prev(node)
+        if result is None:
+            raise gdb.GdbError("No entry in tree")
+
+        return result
+
+
+LxRbPrev()

scripts/gdb/vmlinux-gdb.py

@@ -30,5 +30,6 @@ else:
     import linux.config
     import linux.cpus
     import linux.lists
+    import linux.rbtree
     import linux.proc
     import linux.constants