1 +l4( (  fB- >_I|+?/* SPDX-License-Identifier: GPL-2.0+ */ #ifndef _LINUX_MAPLE_TREE_H #define _LINUX_MAPLE_TREE_H /* * Maple Tree - An RCU-safe adaptive tree for storing ranges * Copyright (c) 2018-2022 Oracle * Authors: Liam R. Howlett * Matthew Wilcox */ #include #include #include /* #define CONFIG_MAPLE_RCU_DISABLED */ /* * Allocated nodes are mutable until they have been inserted into the tree, * at which time they cannot change their type until they have been removed * from the tree and an RCU grace period has passed. * * Removed nodes have their ->parent set to point to themselves. RCU readers * check ->parent before relying on the value that they loaded from the * slots array. This lets us reuse the slots array for the RCU head. * * Nodes in the tree point to their parent unless bit 0 is set. */ #if defined(CONFIG_64BIT) || defined(BUILD_VDSO32_64) /* 64bit sizes */ #define MAPLE_NODE_SLOTS 31 /* 256 bytes including ->parent */ #define MAPLE_RANGE64_SLOTS 16 /* 256 bytes */ #define MAPLE_ARANGE64_SLOTS 10 /* 240 bytes */ #define MAPLE_ALLOC_SLOTS (MAPLE_NODE_SLOTS - 1) #else /* 32bit sizes */ #define MAPLE_NODE_SLOTS 63 /* 256 bytes including ->parent */ #define MAPLE_RANGE64_SLOTS 32 /* 256 bytes */ #define MAPLE_ARANGE64_SLOTS 21 /* 240 bytes */ #define MAPLE_ALLOC_SLOTS (MAPLE_NODE_SLOTS - 2) #endif /* defined(CONFIG_64BIT) || defined(BUILD_VDSO32_64) */ #define MAPLE_NODE_MASK 255UL /* * The node->parent of the root node has bit 0 set and the rest of the pointer * is a pointer to the tree itself. No more bits are available in this pointer * (on m68k, the data structure may only be 2-byte aligned). * * Internal non-root nodes can only have maple_range_* nodes as parents. The * parent pointer is 256B aligned like all other tree nodes. When storing a 32 * or 64 bit values, the offset can fit into 4 bits. The 16 bit values need an * extra bit to store the offset. This extra bit comes from a reuse of the last * bit in the node type. This is possible by using bit 1 to indicate if bit 2 * is part of the type or the slot. * * Once the type is decided, the decision of an allocation range type or a range * type is done by examining the immutable tree flag for the MAPLE_ALLOC_RANGE * flag. * * Node types: * 0x??1 = Root * 0x?00 = 16 bit nodes * 0x010 = 32 bit nodes * 0x110 = 64 bit nodes * * Slot size and location in the parent pointer: * type : slot location * 0x??1 : Root * 0x?00 : 16 bit values, type in 0-1, slot in 2-6 * 0x010 : 32 bit values, type in 0-2, slot in 3-6 * 0x110 : 64 bit values, type in 0-2, slot in 3-6 */ /* * This metadata is used to optimize the gap updating code and in reverse * searching for gaps or any other code that needs to find the end of the data. */ struct maple_metadata { unsigned char end; unsigned char gap; }; /* * Leaf nodes do not store pointers to nodes, they store user data. Users may * store almost any bit pattern. As noted above, the optimisation of storing an * entry at 0 in the root pointer cannot be done for data which have the bottom * two bits set to '10'. We also reserve values with the bottom two bits set to * '10' which are below 4096 (ie 2, 6, 10 .. 4094) for internal use. Some APIs * return errnos as a negative errno shifted right by two bits and the bottom * two bits set to '10', and while choosing to store these values in the array * is not an error, it may lead to confusion if you're testing for an error with * mas_is_err(). * * Non-leaf nodes store the type of the node pointed to (enum maple_type in bits * 3-6), bit 2 is reserved. That leaves bits 0-1 unused for now. * * In regular B-Tree terms, pivots are called keys. The term pivot is used to * indicate that the tree is specifying ranges, Pivots may appear in the * subtree with an entry attached to the value whereas keys are unique to a * specific p