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
8enum {
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 */
71struct 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 */
97struct 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 */
128static inline void get_io_context_active(struct io_context *ioc)
129{
130	WARN_ON_ONCE(atomic_long_read(&ioc->refcount) <= 0);
131	WARN_ON_ONCE(atomic_read(&ioc->active_ref) <= 0);
132	atomic_long_inc(&ioc->refcount);
133	atomic_inc(&ioc->active_ref);
134}
135
136static inline void ioc_task_link(struct io_context *ioc)
137{
138	get_io_context_active(ioc);
139
140	WARN_ON_ONCE(atomic_read(&ioc->nr_tasks) <= 0);
141	atomic_inc(&ioc->nr_tasks);
142}
143
144struct task_struct;
145#ifdef CONFIG_BLOCK
146void put_io_context(struct io_context *ioc);
147void put_io_context_active(struct io_context *ioc);
148void exit_io_context(struct task_struct *task);
149struct io_context *get_task_io_context(struct task_struct *task,
150				       gfp_t gfp_flags, int node);
151#else
152struct io_context;
153static inline void put_io_context(struct io_context *ioc) { }
154static inline void exit_io_context(struct task_struct *task) { }
155#endif
156
157#endif
158