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