Branch data Line data Source code
1 : : #ifndef IOCONTEXT_H
2 : : #define IOCONTEXT_H
3 : :
4 : : #include <linux/radix-tree.h>
5 : : #include <linux/rcupdate.h>
6 : : #include <linux/workqueue.h>
7 : :
8 : : enum {
9 : : ICQ_EXITED = 1 << 2,
10 : : };
11 : :
12 : : /*
13 : : * An io_cq (icq) is association between an io_context (ioc) and a
14 : : * request_queue (q). This is used by elevators which need to track
15 : : * information per ioc - q pair.
16 : : *
17 : : * Elevator can request use of icq by setting elevator_type->icq_size and
18 : : * ->icq_align. Both size and align must be larger than that of struct
19 : : * io_cq and elevator can use the tail area for private information. The
20 : : * recommended way to do this is defining a struct which contains io_cq as
21 : : * the first member followed by private members and using its size and
22 : : * align. For example,
23 : : *
24 : : * struct snail_io_cq {
25 : : * struct io_cq icq;
26 : : * int poke_snail;
27 : : * int feed_snail;
28 : : * };
29 : : *
30 : : * struct elevator_type snail_elv_type {
31 : : * .ops = { ... },
32 : : * .icq_size = sizeof(struct snail_io_cq),
33 : : * .icq_align = __alignof__(struct snail_io_cq),
34 : : * ...
35 : : * };
36 : : *
37 : : * If icq_size is set, block core will manage icq's. All requests will
38 : : * have its ->elv.icq field set before elevator_ops->elevator_set_req_fn()
39 : : * is called and be holding a reference to the associated io_context.
40 : : *
41 : : * Whenever a new icq is created, elevator_ops->elevator_init_icq_fn() is
42 : : * called and, on destruction, ->elevator_exit_icq_fn(). Both functions
43 : : * are called with both the associated io_context and queue locks held.
44 : : *
45 : : * Elevator is allowed to lookup icq using ioc_lookup_icq() while holding
46 : : * queue lock but the returned icq is valid only until the queue lock is
47 : : * released. Elevators can not and should not try to create or destroy
48 : : * icq's.
49 : : *
50 : : * As icq's are linked from both ioc and q, the locking rules are a bit
51 : : * complex.
52 : : *
53 : : * - ioc lock nests inside q lock.
54 : : *
55 : : * - ioc->icq_list and icq->ioc_node are protected by ioc lock.
56 : : * q->icq_list and icq->q_node by q lock.
57 : : *
58 : : * - ioc->icq_tree and ioc->icq_hint are protected by ioc lock, while icq
59 : : * itself is protected by q lock. However, both the indexes and icq
60 : : * itself are also RCU managed and lookup can be performed holding only
61 : : * the q lock.
62 : : *
63 : : * - icq's are not reference counted. They are destroyed when either the
64 : : * ioc or q goes away. Each request with icq set holds an extra
65 : : * reference to ioc to ensure it stays until the request is completed.
66 : : *
67 : : * - Linking and unlinking icq's are performed while holding both ioc and q
68 : : * locks. Due to the lock ordering, q exit is simple but ioc exit
69 : : * requires reverse-order double lock dance.
70 : : */
71 : : struct io_cq {
72 : : struct request_queue *q;
73 : : struct io_context *ioc;
74 : :
75 : : /*
76 : : * q_node and ioc_node link io_cq through icq_list of q and ioc
77 : : * respectively. Both fields are unused once ioc_exit_icq() is
78 : : * called and shared with __rcu_icq_cache and __rcu_head which are
79 : : * used for RCU free of io_cq.
80 : : */
81 : : union {
82 : : struct list_head q_node;
83 : : struct kmem_cache *__rcu_icq_cache;
84 : : };
85 : : union {
86 : : struct hlist_node ioc_node;
87 : : struct rcu_head __rcu_head;
88 : : };
89 : :
90 : : unsigned int flags;
91 : : };
92 : :
93 : : /*
94 : : * I/O subsystem state of the associated processes. It is refcounted
95 : : * and kmalloc'ed. These could be shared between processes.
96 : : */
97 : : struct io_context {
98 : : atomic_long_t refcount;
99 : : atomic_t active_ref;
100 : : atomic_t nr_tasks;
101 : :
102 : : /* all the fields below are protected by this lock */
103 : : spinlock_t lock;
104 : :
105 : : unsigned short ioprio;
106 : :
107 : : /*
108 : : * For request batching
109 : : */
110 : : int nr_batch_requests; /* Number of requests left in the batch */
111 : : unsigned long last_waited; /* Time last woken after wait for request */
112 : :
113 : : struct radix_tree_root icq_tree;
114 : : struct io_cq __rcu *icq_hint;
115 : : struct hlist_head icq_list;
116 : :
117 : : struct work_struct release_work;
118 : : };
119 : :
120 : : /**
121 : : * get_io_context_active - get active reference on ioc
122 : : * @ioc: ioc of interest
123 : : *
124 : : * Only iocs with active reference can issue new IOs. This function
125 : : * acquires an active reference on @ioc. The caller must already have an
126 : : * active reference on @ioc.
127 : : */
128 : : static inline void get_io_context_active(struct io_context *ioc)
129 : : {
130 [ # # ][ # # ]: 0 : WARN_ON_ONCE(atomic_long_read(&ioc->refcount) <= 0);
[ # # ]
131 [ # # ][ # # ]: 0 : WARN_ON_ONCE(atomic_read(&ioc->active_ref) <= 0);
[ # # ]
132 : 0 : atomic_long_inc(&ioc->refcount);
133 : 0 : atomic_inc(&ioc->active_ref);
134 : : }
135 : :
136 : : static inline void ioc_task_link(struct io_context *ioc)
137 : : {
138 : : get_io_context_active(ioc);
139 : :
140 [ # # ][ # # ]: 0 : WARN_ON_ONCE(atomic_read(&ioc->nr_tasks) <= 0);
[ # # ]
141 : 0 : atomic_inc(&ioc->nr_tasks);
142 : : }
143 : :
144 : : struct task_struct;
145 : : #ifdef CONFIG_BLOCK
146 : : void put_io_context(struct io_context *ioc);
147 : : void put_io_context_active(struct io_context *ioc);
148 : : void exit_io_context(struct task_struct *task);
149 : : struct io_context *get_task_io_context(struct task_struct *task,
150 : : gfp_t gfp_flags, int node);
151 : : #else
152 : : struct io_context;
153 : : static inline void put_io_context(struct io_context *ioc) { }
154 : : static inline void exit_io_context(struct task_struct *task) { }
155 : : #endif
156 : :
157 : : #endif
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