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 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 } 135 136 static 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 } 143 144 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 158