alloc_skb--分配skb
dev_alloc_skb--分配skb，通常被设备驱动用在中断上下文中，它是alloc_skb的封装函数，因为在中断处理函数中被调用，因此要求原子操作(GFP_ATOMIC)
kfree_skb--减少skb引用，为0则释放，用于出错丢包时释放skb使用；
dev_kfree_skb==consume_skb--减少skb引用，为0则释放，成功状态下释放skb使用；
1 static inline struct sk_buff *alloc_skb(unsigned int size,
2 gfp_t priority)
3 {
4 return __alloc_skb(size, priority, 0, NUMA_NO_NODE);
5 }
1 /**
2 * __alloc_skb - allocate a network buffer
3 * @size: size to allocate
4 * @gfp_mask: allocation mask
5 * @flags: If SKB_ALLOC_FCLONE is set, allocate from fclone cache
6 * instead of head cache and allocate a cloned (child) skb.
7 * If SKB_ALLOC_RX is set, __GFP_MEMALLOC will be used for
8 * allocations in case the data is required for writeback
9 * @node: numa node to allocate memory on
10 *
11 * Allocate a new &sk_buff. The returned buffer has no headroom and a
12 * tail room of at least size bytes. The object has a reference count
13 * of one. The return is the buffer. On a failure the return is %NULL.
14 *
15 * Buffers may only be allocated from interrupts using a @gfp_mask of
16 * %GFP_ATOMIC.
17 */
18 struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
19 int flags, int node)
20 {
21 struct kmem_cache *cache;
22 struct skb_shared_info *shinfo;
23 struct sk_buff *skb;
24 u8 *data;
25 bool pfmemalloc;
26
27 /* 得到分配使用的高速缓存 */
28 cache = (flags & SKB_ALLOC_FCLONE)
29 ? skbuff_fclone_cache : skbuff_head_cache;
30
31 if (sk_memalloc_socks() && (flags & SKB_ALLOC_RX))
32 gfp_mask |= __GFP_MEMALLOC;
33
34 /* Get the HEAD */
35 /* 分配skb */
36 skb = kmem_cache_alloc_node(cache, gfp_mask & ~__GFP_DMA, node);
37 if (!skb)
38 goto out;
39 prefetchw(skb);
40
41 /* We do our best to align skb_shared_info on a separate cache
42 * line. It usually works because kmalloc(X > SMP_CACHE_BYTES) gives
43 * aligned memory blocks, unless SLUB/SLAB debug is enabled.
44 * Both skb->head and skb_shared_info are cache line aligned.
45 */
46 /* 数据对齐 */
47 size = SKB_DATA_ALIGN(size);
48 /* 对齐后的数据加上skb_shared_info对齐后的大小 */
49 size += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
50
51 //分配数据区
52 data = kmalloc_reserve(size, gfp_mask, node, &pfmemalloc);
53 if (!data)
54 goto nodata;
55 /* kmalloc(size) might give us more room than requested.
56 * Put skb_shared_info exactly at the end of allocated zone,
57 * to allow max possible filling before reallocation.
58 */
59 /* 除了skb_shared_info以外的数据大小 */
60 size = SKB_WITH_OVERHEAD(ksize(data));
61 prefetchw(data + size);
62
63 /*
64 * Only clear those fields we need to clear, not those that we will
65 * actually initialise below. Hence, don‘t put any more fields after
66 * the tail pointer in struct sk_buff!
67 */
68 memset(skb, 0, offsetof(struct sk_buff, tail));
69 /* Account for allocated memory : skb + skb->head */
70 /* 总长度= skb大小+ 数据大小+ skb_shared_info大小 */
71 skb->truesize = SKB_TRUESIZE(size);
72 /* PFMEMALLOC分配标记 */
73 skb->pfmemalloc = pfmemalloc;
74 /* 设置引用计数为1 */
75 atomic_set(&skb->users, 1);
76 /*head data tail均指向数据区头部*/
77 skb->head = data;
78 skb->data = data;
79 skb_reset_tail_pointer(skb);
80
81 /* end指向数据区尾部 */
82 skb->end = skb->tail + size;
83 /* 初始化默认各层header偏移值 */
84 skb->mac_header = (typeof(skb->mac_header))~0U;
85 skb->transport_header = (typeof(skb->transport_header))~0U;
86
87 /* make sure we initialize shinfo sequentially */
88 /* 从end开始的区域为skb_shared_info */
89 shinfo = skb_shinfo(skb);
90 memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
91 /* 设置引用计数为1 */
92 atomic_set(&shinfo->dataref, 1);
93 kmemcheck_annotate_variable(shinfo->destructor_arg);
94
95 /* 如果有克隆标记 */
96 if (flags & SKB_ALLOC_FCLONE) {
97 struct sk_buff_fclones *fclones;
98
99 /* 得到clone结构 */
100 fclones = container_of(skb, struct sk_buff_fclones, skb1);
101
102 kmemcheck_annotate_bitfield(&fclones->skb2, flags1);
103
104 /* 设置克隆标记 */
105 skb->fclone = SKB_FCLONE_ORIG;
106
107 /* 设置引用为1 */
108 atomic_set(&fclones->fclone_ref, 1);
109
110 /* 设置skb2的克隆标记 */
111 fclones->skb2.fclone = SKB_FCLONE_CLONE;
112 }
113 out:
114 return skb;
115 nodata:
116 kmem_cache_free(cache, skb);
117 skb = NULL;
118 goto out;
119 }
1 /* legacy helper around netdev_alloc_skb() */
2 static inline struct sk_buff *dev_alloc_skb(unsigned int length)
3 {
4 return netdev_alloc_skb(NULL, length);
5 }
1 /**
2 * netdev_alloc_skb - allocate an skbuff for rx on a specific device
3 * @dev: network device to receive on
4 * @length: length to allocate
5 *
6 * Allocate a new &sk_buff and assign it a usage count of one. The
7 * buffer has unspecified headroom built in. Users should allocate
8 * the headroom they think they need without accounting for the
9 * built in space. The built in space is used for optimisations.
10 *
11 * %NULL is returned if there is no free memory. Although this function
12 * allocates memory it can be called from an interrupt.
13 */
14 static inline struct sk_buff *netdev_alloc_skb(struct net_device *dev,
15 unsigned int length)
16 {
17 return __netdev_alloc_skb(dev, length, GFP_ATOMIC);
18 }
1 /**
2 * __netdev_alloc_skb - allocate an skbuff for rx on a specific device
3 * @dev: network device to receive on
4 * @len: length to allocate
5 * @gfp_mask: get_free_pages mask, passed to alloc_skb
6 *
7 * Allocate a new &sk_buff and assign it a usage count of one. The
8 * buffer has NET_SKB_PAD headroom built in. Users should allocate
9 * the headroom they think they need without accounting for the
10 * built in space. The built in space is used for optimisations.
11 *
12 * %NULL is returned if there is no free memory.
13 */
14 struct sk_buff *__netdev_alloc_skb(struct net_device *dev, unsigned int len,
15 gfp_t gfp_mask)
16 {
17 struct page_frag_cache *nc;
18 unsigned long flags;
19 struct sk_buff *skb;
20 bool pfmemalloc;
21 void *data;
22
23 len += NET_SKB_PAD;
24
25 /*
26 分配长度+ skb_shared_info长度> 一页
27 有__GFP_DIRECT_RECLAIM | GFP_DMA 标记
28 */
29 if ((len > SKB_WITH_OVERHEAD(PAGE_SIZE)) ||
30 (gfp_mask & (__GFP_DIRECT_RECLAIM | GFP_DMA))) {
31 /* 通过__alloc_skb分配内存*/
32 skb = __alloc_skb(len, gfp_mask, SKB_ALLOC_RX, NUMA_NO_NODE);
33 if (!skb)
34 goto skb_fail;
35
36 /* 分配成功 */
37 goto skb_success;
38 }
39
40 /* 分配长度+ skb_shared_info长度*/
41 len += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
42 /* 对整个长度进行对齐 */
43 len = SKB_DATA_ALIGN(len);
44
45 if (sk_memalloc_socks())
46 gfp_mask |= __GFP_MEMALLOC;
47
48 /* 保存中断 */
49 local_irq_save(flags);
50
51 nc = this_cpu_ptr(&netdev_alloc_cache);
52 /* 分配空间 */
53 data = page_frag_alloc(nc, len, gfp_mask);
54 pfmemalloc = nc->pfmemalloc;
55
56 /* 恢复中断 */
57 local_irq_restore(flags);
58
59 if (unlikely(!data))
60 return NULL;
61
62 /* 构建skb */
63 skb = __build_skb(data, len);
64 if (unlikely(!skb)) {
65 skb_free_frag(data);
66 return NULL;
67 }
68
69 /* use OR instead of assignment to avoid clearing of bits in mask */
70 /* 设置PFMEMALLOC标记 */
71 if (pfmemalloc)
72 skb->pfmemalloc = 1;
73
74 //打内存分配标记
75 skb->head_frag = 1;
76
77 skb_success:
78 /* 保留空间 */
79 skb_reserve(skb, NET_SKB_PAD);
80 /* 设置输入设备 */
81 skb->dev = dev;
82
83 skb_fail:
84 return skb;
85 }
---free系列---
1 /**
2 * kfree_skb - free an sk_buff
3 * @skb: buffer to free
4 *
5 * Drop a reference to the buffer and free it if the usage count has
6 * hit zero.
7 */
8 /*
9 释放skb
10 */
11 void kfree_skb(struct sk_buff *skb)
12 {
13 if (unlikely(!skb))
14 return;
15 /* 引用为1，可直接释放 */
16 if (likely(atomic_read(&skb->users) == 1))
17 smp_rmb();
18 /*
19 对引用减1，并且判断，如果结果不为0
20 说明还有引用，返回
21 */
22 else if (likely(!atomic_dec_and_test(&skb->users)))
23 return;
24 trace_kfree_skb(skb, __builtin_return_address(0));
25
26 //真正的skb释放
27 __kfree_skb(skb);
28 }
1 /**
2 * __kfree_skb - private function
3 * @skb: buffer
4 *
5 * Free an sk_buff. Release anything attached to the buffer.
6 * Clean the state. This is an internal helper function. Users should
7 * always call kfree_skb
8 */
9 /* 释放skb */
10 void __kfree_skb(struct sk_buff *skb)
11 {
12 /* 释放skb附带的所有数据 */
13 skb_release_all(skb);
14 /* 释放skb */
15 kfree_skbmem(skb);
16 }
1 #define dev_kfree_skb(a) consume_skb(a)
1 /**
2 * consume_skb - free an skbuff
3 * @skb: buffer to free
4 *
5 * Drop a ref to the buffer and free it if the usage count has hit zero
6 * Functions identically to kfree_skb, but kfree_skb assumes that the frame
7 * is being dropped after a failure and notes that
8 */
9 /* 释放skb，与kfree_skb区别是，kfree_skb用于失败时丢包释放 */
10 void consume_skb(struct sk_buff *skb)
11 {
12 if (unlikely(!skb))
13 return;
14 if (likely(atomic_read(&skb->users) == 1))
15 smp_rmb();
16 else if (likely(!atomic_dec_and_test(&skb->users)))
17 return;
18 trace_consume_skb(skb);
19 __kfree_skb(skb);
20 }
时间： 2024-10-27 18:03:27