This trie implements a longest prefix match algorithm that can be used to match IP addresses to a stored set of ranges. Internally, data is stored in an unbalanced trie of nodes that has a maximum height of n, where n is the prefixlen the trie was created with. Tries may be created with prefix lengths that are multiples of 8, in the range from 8 to 2048. The key used for lookup and update operations is a struct bpf_lpm_trie_key, and the value is a uint64_t. The code carries more information about the internal implementation. Signed-off-by: Daniel Mack <daniel@zonque.org> Reviewed-by: David Herrmann <dh.herrmann@gmail.com> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>tirimbino
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/*
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* Longest prefix match list implementation |
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* |
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* Copyright (c) 2016,2017 Daniel Mack |
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* Copyright (c) 2016 David Herrmann |
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* |
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* This file is subject to the terms and conditions of version 2 of the GNU |
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* General Public License. See the file COPYING in the main directory of the |
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* Linux distribution for more details. |
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*/ |
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#include <linux/bpf.h> |
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#include <linux/err.h> |
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#include <linux/slab.h> |
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#include <linux/spinlock.h> |
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#include <linux/vmalloc.h> |
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#include <net/ipv6.h> |
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|
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/* Intermediate node */ |
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#define LPM_TREE_NODE_FLAG_IM BIT(0) |
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struct lpm_trie_node; |
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struct lpm_trie_node { |
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struct rcu_head rcu; |
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struct lpm_trie_node __rcu *child[2]; |
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u32 prefixlen; |
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u32 flags; |
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u8 data[0]; |
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}; |
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struct lpm_trie { |
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struct bpf_map map; |
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struct lpm_trie_node __rcu *root; |
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size_t n_entries; |
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size_t max_prefixlen; |
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size_t data_size; |
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raw_spinlock_t lock; |
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}; |
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|
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/* This trie implements a longest prefix match algorithm that can be used to
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* match IP addresses to a stored set of ranges. |
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* |
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* Data stored in @data of struct bpf_lpm_key and struct lpm_trie_node is |
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* interpreted as big endian, so data[0] stores the most significant byte. |
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* |
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* Match ranges are internally stored in instances of struct lpm_trie_node |
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* which each contain their prefix length as well as two pointers that may |
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* lead to more nodes containing more specific matches. Each node also stores |
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* a value that is defined by and returned to userspace via the update_elem |
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* and lookup functions. |
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* |
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* For instance, let's start with a trie that was created with a prefix length |
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* of 32, so it can be used for IPv4 addresses, and one single element that |
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* matches 192.168.0.0/16. The data array would hence contain |
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* [0xc0, 0xa8, 0x00, 0x00] in big-endian notation. This documentation will |
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* stick to IP-address notation for readability though. |
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* |
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* As the trie is empty initially, the new node (1) will be places as root |
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* node, denoted as (R) in the example below. As there are no other node, both |
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* child pointers are %NULL. |
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* |
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* +----------------+ |
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* | (1) (R) | |
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* | 192.168.0.0/16 | |
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* | value: 1 | |
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* | [0] [1] | |
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* +----------------+ |
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* |
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* Next, let's add a new node (2) matching 192.168.0.0/24. As there is already |
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* a node with the same data and a smaller prefix (ie, a less specific one), |
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* node (2) will become a child of (1). In child index depends on the next bit |
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* that is outside of what (1) matches, and that bit is 0, so (2) will be |
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* child[0] of (1): |
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* |
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* +----------------+ |
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* | (1) (R) | |
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* | 192.168.0.0/16 | |
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* | value: 1 | |
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* | [0] [1] | |
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* +----------------+ |
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* | |
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* +----------------+ |
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* | (2) | |
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* | 192.168.0.0/24 | |
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* | value: 2 | |
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* | [0] [1] | |
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* +----------------+ |
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* |
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* The child[1] slot of (1) could be filled with another node which has bit #17 |
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* (the next bit after the ones that (1) matches on) set to 1. For instance, |
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* 192.168.128.0/24: |
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* |
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* +----------------+ |
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* | (1) (R) | |
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* | 192.168.0.0/16 | |
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* | value: 1 | |
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* | [0] [1] | |
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* +----------------+ |
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* | | |
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* +----------------+ +------------------+ |
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* | (2) | | (3) | |
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* | 192.168.0.0/24 | | 192.168.128.0/24 | |
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* | value: 2 | | value: 3 | |
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* | [0] [1] | | [0] [1] | |
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* +----------------+ +------------------+ |
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* |
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* Let's add another node (4) to the game for 192.168.1.0/24. In order to place |
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* it, node (1) is looked at first, and because (4) of the semantics laid out |
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* above (bit #17 is 0), it would normally be attached to (1) as child[0]. |
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* However, that slot is already allocated, so a new node is needed in between. |
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* That node does not have a value attached to it and it will never be |
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* returned to users as result of a lookup. It is only there to differentiate |
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* the traversal further. It will get a prefix as wide as necessary to |
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* distinguish its two children: |
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* |
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* +----------------+ |
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* | (1) (R) | |
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* | 192.168.0.0/16 | |
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* | value: 1 | |
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* | [0] [1] | |
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* +----------------+ |
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* | | |
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* +----------------+ +------------------+ |
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* | (4) (I) | | (3) | |
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* | 192.168.0.0/23 | | 192.168.128.0/24 | |
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* | value: --- | | value: 3 | |
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* | [0] [1] | | [0] [1] | |
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* +----------------+ +------------------+ |
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* | | |
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* +----------------+ +----------------+ |
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* | (2) | | (5) | |
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* | 192.168.0.0/24 | | 192.168.1.0/24 | |
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* | value: 2 | | value: 5 | |
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* | [0] [1] | | [0] [1] | |
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* +----------------+ +----------------+ |
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* |
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* 192.168.1.1/32 would be a child of (5) etc. |
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* |
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* An intermediate node will be turned into a 'real' node on demand. In the |
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* example above, (4) would be re-used if 192.168.0.0/23 is added to the trie. |
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* |
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* A fully populated trie would have a height of 32 nodes, as the trie was |
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* created with a prefix length of 32. |
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* |
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* The lookup starts at the root node. If the current node matches and if there |
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* is a child that can be used to become more specific, the trie is traversed |
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* downwards. The last node in the traversal that is a non-intermediate one is |
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* returned. |
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*/ |
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static inline int extract_bit(const u8 *data, size_t index) |
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{ |
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return !!(data[index / 8] & (1 << (7 - (index % 8)))); |
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} |
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/**
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* longest_prefix_match() - determine the longest prefix |
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* @trie: The trie to get internal sizes from |
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* @node: The node to operate on |
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* @key: The key to compare to @node |
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* |
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* Determine the longest prefix of @node that matches the bits in @key. |
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*/ |
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static size_t longest_prefix_match(const struct lpm_trie *trie, |
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const struct lpm_trie_node *node, |
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const struct bpf_lpm_trie_key *key) |
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{ |
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size_t prefixlen = 0; |
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size_t i; |
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for (i = 0; i < trie->data_size; i++) { |
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size_t b; |
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b = 8 - fls(node->data[i] ^ key->data[i]); |
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prefixlen += b; |
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if (prefixlen >= node->prefixlen || prefixlen >= key->prefixlen) |
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return min(node->prefixlen, key->prefixlen); |
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if (b < 8) |
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break; |
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} |
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return prefixlen; |
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} |
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/* Called from syscall or from eBPF program */ |
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static void *trie_lookup_elem(struct bpf_map *map, void *_key) |
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{ |
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struct lpm_trie *trie = container_of(map, struct lpm_trie, map); |
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struct lpm_trie_node *node, *found = NULL; |
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struct bpf_lpm_trie_key *key = _key; |
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/* Start walking the trie from the root node ... */ |
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for (node = rcu_dereference(trie->root); node;) { |
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unsigned int next_bit; |
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size_t matchlen; |
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/* Determine the longest prefix of @node that matches @key.
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* If it's the maximum possible prefix for this trie, we have |
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* an exact match and can return it directly. |
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*/ |
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matchlen = longest_prefix_match(trie, node, key); |
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if (matchlen == trie->max_prefixlen) { |
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found = node; |
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break; |
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} |
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/* If the number of bits that match is smaller than the prefix
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* length of @node, bail out and return the node we have seen |
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* last in the traversal (ie, the parent). |
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*/ |
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if (matchlen < node->prefixlen) |
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break; |
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/* Consider this node as return candidate unless it is an
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* artificially added intermediate one. |
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*/ |
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if (!(node->flags & LPM_TREE_NODE_FLAG_IM)) |
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found = node; |
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/* If the node match is fully satisfied, let's see if we can
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* become more specific. Determine the next bit in the key and |
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* traverse down. |
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*/ |
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next_bit = extract_bit(key->data, node->prefixlen); |
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node = rcu_dereference(node->child[next_bit]); |
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} |
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if (!found) |
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return NULL; |
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return found->data + trie->data_size; |
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} |
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static struct lpm_trie_node *lpm_trie_node_alloc(const struct lpm_trie *trie, |
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const void *value) |
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{ |
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struct lpm_trie_node *node; |
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size_t size = sizeof(struct lpm_trie_node) + trie->data_size; |
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if (value) |
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size += trie->map.value_size; |
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node = kmalloc(size, GFP_ATOMIC | __GFP_NOWARN); |
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if (!node) |
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return NULL; |
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node->flags = 0; |
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if (value) |
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memcpy(node->data + trie->data_size, value, |
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trie->map.value_size); |
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return node; |
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} |
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/* Called from syscall or from eBPF program */ |
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static int trie_update_elem(struct bpf_map *map, |
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void *_key, void *value, u64 flags) |
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{ |
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struct lpm_trie *trie = container_of(map, struct lpm_trie, map); |
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struct lpm_trie_node *node, *im_node, *new_node = NULL; |
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struct lpm_trie_node __rcu **slot; |
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struct bpf_lpm_trie_key *key = _key; |
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unsigned long irq_flags; |
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unsigned int next_bit; |
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size_t matchlen = 0; |
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int ret = 0; |
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if (unlikely(flags > BPF_EXIST)) |
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return -EINVAL; |
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if (key->prefixlen > trie->max_prefixlen) |
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return -EINVAL; |
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raw_spin_lock_irqsave(&trie->lock, irq_flags); |
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/* Allocate and fill a new node */ |
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if (trie->n_entries == trie->map.max_entries) { |
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ret = -ENOSPC; |
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goto out; |
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} |
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new_node = lpm_trie_node_alloc(trie, value); |
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if (!new_node) { |
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ret = -ENOMEM; |
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goto out; |
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} |
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trie->n_entries++; |
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new_node->prefixlen = key->prefixlen; |
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RCU_INIT_POINTER(new_node->child[0], NULL); |
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RCU_INIT_POINTER(new_node->child[1], NULL); |
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memcpy(new_node->data, key->data, trie->data_size); |
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/* Now find a slot to attach the new node. To do that, walk the tree
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* from the root and match as many bits as possible for each node until |
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* we either find an empty slot or a slot that needs to be replaced by |
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* an intermediate node. |
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*/ |
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slot = &trie->root; |
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while ((node = rcu_dereference_protected(*slot, |
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lockdep_is_held(&trie->lock)))) { |
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matchlen = longest_prefix_match(trie, node, key); |
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if (node->prefixlen != matchlen || |
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node->prefixlen == key->prefixlen || |
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node->prefixlen == trie->max_prefixlen) |
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break; |
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next_bit = extract_bit(key->data, node->prefixlen); |
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slot = &node->child[next_bit]; |
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} |
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/* If the slot is empty (a free child pointer or an empty root),
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* simply assign the @new_node to that slot and be done. |
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*/ |
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if (!node) { |
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rcu_assign_pointer(*slot, new_node); |
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goto out; |
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} |
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/* If the slot we picked already exists, replace it with @new_node
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* which already has the correct data array set. |
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*/ |
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if (node->prefixlen == matchlen) { |
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new_node->child[0] = node->child[0]; |
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new_node->child[1] = node->child[1]; |
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if (!(node->flags & LPM_TREE_NODE_FLAG_IM)) |
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trie->n_entries--; |
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rcu_assign_pointer(*slot, new_node); |
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kfree_rcu(node, rcu); |
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goto out; |
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} |
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/* If the new node matches the prefix completely, it must be inserted
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* as an ancestor. Simply insert it between @node and *@slot. |
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*/ |
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if (matchlen == key->prefixlen) { |
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next_bit = extract_bit(node->data, matchlen); |
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rcu_assign_pointer(new_node->child[next_bit], node); |
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rcu_assign_pointer(*slot, new_node); |
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goto out; |
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} |
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im_node = lpm_trie_node_alloc(trie, NULL); |
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if (!im_node) { |
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ret = -ENOMEM; |
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goto out; |
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} |
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im_node->prefixlen = matchlen; |
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im_node->flags |= LPM_TREE_NODE_FLAG_IM; |
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memcpy(im_node->data, node->data, trie->data_size); |
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/* Now determine which child to install in which slot */ |
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if (extract_bit(key->data, matchlen)) { |
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rcu_assign_pointer(im_node->child[0], node); |
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rcu_assign_pointer(im_node->child[1], new_node); |
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} else { |
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rcu_assign_pointer(im_node->child[0], new_node); |
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rcu_assign_pointer(im_node->child[1], node); |
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} |
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/* Finally, assign the intermediate node to the determined spot */ |
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rcu_assign_pointer(*slot, im_node); |
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out: |
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if (ret) { |
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if (new_node) |
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trie->n_entries--; |
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kfree(new_node); |
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kfree(im_node); |
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} |
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raw_spin_unlock_irqrestore(&trie->lock, irq_flags); |
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return ret; |
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} |
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static int trie_delete_elem(struct bpf_map *map, void *key) |
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{ |
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/* TODO */ |
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return -ENOSYS; |
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} |
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static struct bpf_map *trie_alloc(union bpf_attr *attr) |
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{ |
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size_t cost, cost_per_node; |
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struct lpm_trie *trie; |
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int ret; |
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if (!capable(CAP_SYS_ADMIN)) |
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return ERR_PTR(-EPERM); |
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/* check sanity of attributes */ |
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if (attr->max_entries == 0 || |
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attr->map_flags != BPF_F_NO_PREALLOC || |
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attr->key_size < sizeof(struct bpf_lpm_trie_key) + 1 || |
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attr->key_size > sizeof(struct bpf_lpm_trie_key) + 256 || |
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attr->value_size == 0) |
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return ERR_PTR(-EINVAL); |
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trie = kzalloc(sizeof(*trie), GFP_USER | __GFP_NOWARN); |
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if (!trie) |
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return ERR_PTR(-ENOMEM); |
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|
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/* copy mandatory map attributes */ |
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trie->map.map_type = attr->map_type; |
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trie->map.key_size = attr->key_size; |
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trie->map.value_size = attr->value_size; |
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trie->map.max_entries = attr->max_entries; |
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trie->data_size = attr->key_size - |
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offsetof(struct bpf_lpm_trie_key, data); |
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trie->max_prefixlen = trie->data_size * 8; |
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|
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cost_per_node = sizeof(struct lpm_trie_node) + |
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attr->value_size + trie->data_size; |
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cost = sizeof(*trie) + attr->max_entries * cost_per_node; |
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trie->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT; |
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|
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ret = bpf_map_precharge_memlock(trie->map.pages); |
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if (ret) { |
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kfree(trie); |
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return ERR_PTR(ret); |
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} |
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|
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raw_spin_lock_init(&trie->lock); |
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return &trie->map; |
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} |
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static void trie_free(struct bpf_map *map) |
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{ |
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struct lpm_trie *trie = container_of(map, struct lpm_trie, map); |
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struct lpm_trie_node __rcu **slot; |
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struct lpm_trie_node *node; |
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|
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raw_spin_lock(&trie->lock); |
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|
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/* Always start at the root and walk down to a node that has no
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* children. Then free that node, nullify its reference in the parent |
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* and start over. |
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*/ |
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|
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for (;;) { |
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slot = &trie->root; |
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for (;;) { |
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node = rcu_dereference_protected(*slot, |
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lockdep_is_held(&trie->lock)); |
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if (!node) |
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goto unlock; |
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|
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if (rcu_access_pointer(node->child[0])) { |
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slot = &node->child[0]; |
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continue; |
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} |
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|
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if (rcu_access_pointer(node->child[1])) { |
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slot = &node->child[1]; |
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continue; |
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} |
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|
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kfree(node); |
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RCU_INIT_POINTER(*slot, NULL); |
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break; |
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} |
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} |
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|
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unlock: |
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raw_spin_unlock(&trie->lock); |
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} |
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|
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static const struct bpf_map_ops trie_ops = { |
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.map_alloc = trie_alloc, |
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.map_free = trie_free, |
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.map_lookup_elem = trie_lookup_elem, |
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.map_update_elem = trie_update_elem, |
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.map_delete_elem = trie_delete_elem, |
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}; |
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|
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static struct bpf_map_type_list trie_type __read_mostly = { |
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.ops = &trie_ops, |
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.type = BPF_MAP_TYPE_LPM_TRIE, |
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}; |
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|
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static int __init register_trie_map(void) |
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{ |
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bpf_register_map_type(&trie_type); |
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return 0; |
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} |
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late_initcall(register_trie_map); |
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Reference in new issue