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TOMOYO Linux Cross Reference
Linux/include/linux/iocontext.h

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  1 /* SPDX-License-Identifier: GPL-2.0 */
  2 #ifndef IOCONTEXT_H
  3 #define IOCONTEXT_H
  4 
  5 #include <linux/radix-tree.h>
  6 #include <linux/rcupdate.h>
  7 #include <linux/workqueue.h>
  8 
  9 enum {
 10         ICQ_EXITED              = 1 << 2,
 11 };
 12 
 13 /*
 14  * An io_cq (icq) is association between an io_context (ioc) and a
 15  * request_queue (q).  This is used by elevators which need to track
 16  * information per ioc - q pair.
 17  *
 18  * Elevator can request use of icq by setting elevator_type->icq_size and
 19  * ->icq_align.  Both size and align must be larger than that of struct
 20  * io_cq and elevator can use the tail area for private information.  The
 21  * recommended way to do this is defining a struct which contains io_cq as
 22  * the first member followed by private members and using its size and
 23  * align.  For example,
 24  *
 25  *      struct snail_io_cq {
 26  *              struct io_cq    icq;
 27  *              int             poke_snail;
 28  *              int             feed_snail;
 29  *      };
 30  *
 31  *      struct elevator_type snail_elv_type {
 32  *              .ops =          { ... },
 33  *              .icq_size =     sizeof(struct snail_io_cq),
 34  *              .icq_align =    __alignof__(struct snail_io_cq),
 35  *              ...
 36  *      };
 37  *
 38  * If icq_size is set, block core will manage icq's.  All requests will
 39  * have its ->elv.icq field set before elevator_ops->elevator_set_req_fn()
 40  * is called and be holding a reference to the associated io_context.
 41  *
 42  * Whenever a new icq is created, elevator_ops->elevator_init_icq_fn() is
 43  * called and, on destruction, ->elevator_exit_icq_fn().  Both functions
 44  * are called with both the associated io_context and queue locks held.
 45  *
 46  * Elevator is allowed to lookup icq using ioc_lookup_icq() while holding
 47  * queue lock but the returned icq is valid only until the queue lock is
 48  * released.  Elevators can not and should not try to create or destroy
 49  * icq's.
 50  *
 51  * As icq's are linked from both ioc and q, the locking rules are a bit
 52  * complex.
 53  *
 54  * - ioc lock nests inside q lock.
 55  *
 56  * - ioc->icq_list and icq->ioc_node are protected by ioc lock.
 57  *   q->icq_list and icq->q_node by q lock.
 58  *
 59  * - ioc->icq_tree and ioc->icq_hint are protected by ioc lock, while icq
 60  *   itself is protected by q lock.  However, both the indexes and icq
 61  *   itself are also RCU managed and lookup can be performed holding only
 62  *   the q lock.
 63  *
 64  * - icq's are not reference counted.  They are destroyed when either the
 65  *   ioc or q goes away.  Each request with icq set holds an extra
 66  *   reference to ioc to ensure it stays until the request is completed.
 67  *
 68  * - Linking and unlinking icq's are performed while holding both ioc and q
 69  *   locks.  Due to the lock ordering, q exit is simple but ioc exit
 70  *   requires reverse-order double lock dance.
 71  */
 72 struct io_cq {
 73         struct request_queue    *q;
 74         struct io_context       *ioc;
 75 
 76         /*
 77          * q_node and ioc_node link io_cq through icq_list of q and ioc
 78          * respectively.  Both fields are unused once ioc_exit_icq() is
 79          * called and shared with __rcu_icq_cache and __rcu_head which are
 80          * used for RCU free of io_cq.
 81          */
 82         union {
 83                 struct list_head        q_node;
 84                 struct kmem_cache       *__rcu_icq_cache;
 85         };
 86         union {
 87                 struct hlist_node       ioc_node;
 88                 struct rcu_head         __rcu_head;
 89         };
 90 
 91         unsigned int            flags;
 92 };
 93 
 94 /*
 95  * I/O subsystem state of the associated processes.  It is refcounted
 96  * and kmalloc'ed. These could be shared between processes.
 97  */
 98 struct io_context {
 99         atomic_long_t refcount;
100         atomic_t active_ref;
101         atomic_t nr_tasks;
102 
103         /* all the fields below are protected by this lock */
104         spinlock_t lock;
105 
106         unsigned short ioprio;
107 
108         /*
109          * For request batching
110          */
111         int nr_batch_requests;     /* Number of requests left in the batch */
112         unsigned long last_waited; /* Time last woken after wait for request */
113 
114         struct radix_tree_root  icq_tree;
115         struct io_cq __rcu      *icq_hint;
116         struct hlist_head       icq_list;
117 
118         struct work_struct release_work;
119 };
120 
121 /**
122  * get_io_context_active - get active reference on ioc
123  * @ioc: ioc of interest
124  *
125  * Only iocs with active reference can issue new IOs.  This function
126  * acquires an active reference on @ioc.  The caller must already have an
127  * active reference on @ioc.
128  */
129 static inline void get_io_context_active(struct io_context *ioc)
130 {
131         WARN_ON_ONCE(atomic_long_read(&ioc->refcount) <= 0);
132         WARN_ON_ONCE(atomic_read(&ioc->active_ref) <= 0);
133         atomic_long_inc(&ioc->refcount);
134         atomic_inc(&ioc->active_ref);
135 }
136 
137 static inline void ioc_task_link(struct io_context *ioc)
138 {
139         get_io_context_active(ioc);
140 
141         WARN_ON_ONCE(atomic_read(&ioc->nr_tasks) <= 0);
142         atomic_inc(&ioc->nr_tasks);
143 }
144 
145 struct task_struct;
146 #ifdef CONFIG_BLOCK
147 void put_io_context(struct io_context *ioc);
148 void put_io_context_active(struct io_context *ioc);
149 void exit_io_context(struct task_struct *task);
150 struct io_context *get_task_io_context(struct task_struct *task,
151                                        gfp_t gfp_flags, int node);
152 #else
153 struct io_context;
154 static inline void put_io_context(struct io_context *ioc) { }
155 static inline void exit_io_context(struct task_struct *task) { }
156 #endif
157 
158 #endif
159 

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