--- /dev/null
+#ifndef IOCONTEXT_H
+#define IOCONTEXT_H
+
+#include <linux/radix-tree.h>
+#include <linux/rcupdate.h>
+#include <linux/workqueue.h>
+
+enum {
+ ICQ_EXITED = 1 << 2,
+};
+
+/*
+ * An io_cq (icq) is association between an io_context (ioc) and a
+ * request_queue (q). This is used by elevators which need to track
+ * information per ioc - q pair.
+ *
+ * Elevator can request use of icq by setting elevator_type->icq_size and
+ * ->icq_align. Both size and align must be larger than that of struct
+ * io_cq and elevator can use the tail area for private information. The
+ * recommended way to do this is defining a struct which contains io_cq as
+ * the first member followed by private members and using its size and
+ * align. For example,
+ *
+ * struct snail_io_cq {
+ * struct io_cq icq;
+ * int poke_snail;
+ * int feed_snail;
+ * };
+ *
+ * struct elevator_type snail_elv_type {
+ * .ops = { ... },
+ * .icq_size = sizeof(struct snail_io_cq),
+ * .icq_align = __alignof__(struct snail_io_cq),
+ * ...
+ * };
+ *
+ * If icq_size is set, block core will manage icq's. All requests will
+ * have its ->elv.icq field set before elevator_ops->elevator_set_req_fn()
+ * is called and be holding a reference to the associated io_context.
+ *
+ * Whenever a new icq is created, elevator_ops->elevator_init_icq_fn() is
+ * called and, on destruction, ->elevator_exit_icq_fn(). Both functions
+ * are called with both the associated io_context and queue locks held.
+ *
+ * Elevator is allowed to lookup icq using ioc_lookup_icq() while holding
+ * queue lock but the returned icq is valid only until the queue lock is
+ * released. Elevators can not and should not try to create or destroy
+ * icq's.
+ *
+ * As icq's are linked from both ioc and q, the locking rules are a bit
+ * complex.
+ *
+ * - ioc lock nests inside q lock.
+ *
+ * - ioc->icq_list and icq->ioc_node are protected by ioc lock.
+ * q->icq_list and icq->q_node by q lock.
+ *
+ * - ioc->icq_tree and ioc->icq_hint are protected by ioc lock, while icq
+ * itself is protected by q lock. However, both the indexes and icq
+ * itself are also RCU managed and lookup can be performed holding only
+ * the q lock.
+ *
+ * - icq's are not reference counted. They are destroyed when either the
+ * ioc or q goes away. Each request with icq set holds an extra
+ * reference to ioc to ensure it stays until the request is completed.
+ *
+ * - Linking and unlinking icq's are performed while holding both ioc and q
+ * locks. Due to the lock ordering, q exit is simple but ioc exit
+ * requires reverse-order double lock dance.
+ */
+struct io_cq {
+ struct request_queue *q;
+ struct io_context *ioc;
+
+ /*
+ * q_node and ioc_node link io_cq through icq_list of q and ioc
+ * respectively. Both fields are unused once ioc_exit_icq() is
+ * called and shared with __rcu_icq_cache and __rcu_head which are
+ * used for RCU free of io_cq.
+ */
+ union {
+ struct list_head q_node;
+ struct kmem_cache *__rcu_icq_cache;
+ };
+ union {
+ struct hlist_node ioc_node;
+ struct rcu_head __rcu_head;
+ };
+
+ unsigned int flags;
+};
+
+/*
+ * I/O subsystem state of the associated processes. It is refcounted
+ * and kmalloc'ed. These could be shared between processes.
+ */
+struct io_context {
+ atomic_long_t refcount;
+ atomic_t active_ref;
+ atomic_t nr_tasks;
+
+ /* all the fields below are protected by this lock */
+ spinlock_t lock;
+
+ unsigned short ioprio;
+
+ /*
+ * For request batching
+ */
+ int nr_batch_requests; /* Number of requests left in the batch */
+ unsigned long last_waited; /* Time last woken after wait for request */
+
+ struct radix_tree_root icq_tree;
+ struct io_cq __rcu *icq_hint;
+ struct hlist_head icq_list;
+
+ struct work_struct release_work;
+};
+
+/**
+ * get_io_context_active - get active reference on ioc
+ * @ioc: ioc of interest
+ *
+ * Only iocs with active reference can issue new IOs. This function
+ * acquires an active reference on @ioc. The caller must already have an
+ * active reference on @ioc.
+ */
+static inline void get_io_context_active(struct io_context *ioc)
+{
+ WARN_ON_ONCE(atomic_long_read(&ioc->refcount) <= 0);
+ WARN_ON_ONCE(atomic_read(&ioc->active_ref) <= 0);
+ atomic_long_inc(&ioc->refcount);
+ atomic_inc(&ioc->active_ref);
+}
+
+static inline void ioc_task_link(struct io_context *ioc)
+{
+ get_io_context_active(ioc);
+
+ WARN_ON_ONCE(atomic_read(&ioc->nr_tasks) <= 0);
+ atomic_inc(&ioc->nr_tasks);
+}
+
+struct task_struct;
+#ifdef CONFIG_BLOCK
+void put_io_context(struct io_context *ioc);
+void put_io_context_active(struct io_context *ioc);
+void exit_io_context(struct task_struct *task);
+struct io_context *get_task_io_context(struct task_struct *task,
+ gfp_t gfp_flags, int node);
+#else
+struct io_context;
+static inline void put_io_context(struct io_context *ioc) { }
+static inline void exit_io_context(struct task_struct *task) { }
+#endif
+
+#endif
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