Line data    Source code

       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             :         ICQ_DESTROYED           = 1 << 3,
      12             : };
      13             : 
      14             : /*
      15             :  * An io_cq (icq) is association between an io_context (ioc) and a
      16             :  * request_queue (q).  This is used by elevators which need to track
      17             :  * information per ioc - q pair.
      18             :  *
      19             :  * Elevator can request use of icq by setting elevator_type->icq_size and
      20             :  * ->icq_align.  Both size and align must be larger than that of struct
      21             :  * io_cq and elevator can use the tail area for private information.  The
      22             :  * recommended way to do this is defining a struct which contains io_cq as
      23             :  * the first member followed by private members and using its size and
      24             :  * align.  For example,
      25             :  *
      26             :  *      struct snail_io_cq {
      27             :  *              struct io_cq    icq;
      28             :  *              int             poke_snail;
      29             :  *              int             feed_snail;
      30             :  *      };
      31             :  *
      32             :  *      struct elevator_type snail_elv_type {
      33             :  *              .ops =          { ... },
      34             :  *              .icq_size =     sizeof(struct snail_io_cq),
      35             :  *              .icq_align =    __alignof__(struct snail_io_cq),
      36             :  *              ...
      37             :  *      };
      38             :  *
      39             :  * If icq_size is set, block core will manage icq's.  All requests will
      40             :  * have its ->elv.icq field set before elevator_ops->elevator_set_req_fn()
      41             :  * is called and be holding a reference to the associated io_context.
      42             :  *
      43             :  * Whenever a new icq is created, elevator_ops->elevator_init_icq_fn() is
      44             :  * called and, on destruction, ->elevator_exit_icq_fn().  Both functions
      45             :  * are called with both the associated io_context and queue locks held.
      46             :  *
      47             :  * Elevator is allowed to lookup icq using ioc_lookup_icq() while holding
      48             :  * queue lock but the returned icq is valid only until the queue lock is
      49             :  * released.  Elevators can not and should not try to create or destroy
      50             :  * icq's.
      51             :  *
      52             :  * As icq's are linked from both ioc and q, the locking rules are a bit
      53             :  * complex.
      54             :  *
      55             :  * - ioc lock nests inside q lock.
      56             :  *
      57             :  * - ioc->icq_list and icq->ioc_node are protected by ioc lock.
      58             :  *   q->icq_list and icq->q_node by q lock.
      59             :  *
      60             :  * - ioc->icq_tree and ioc->icq_hint are protected by ioc lock, while icq
      61             :  *   itself is protected by q lock.  However, both the indexes and icq
      62             :  *   itself are also RCU managed and lookup can be performed holding only
      63             :  *   the q lock.
      64             :  *
      65             :  * - icq's are not reference counted.  They are destroyed when either the
      66             :  *   ioc or q goes away.  Each request with icq set holds an extra
      67             :  *   reference to ioc to ensure it stays until the request is completed.
      68             :  *
      69             :  * - Linking and unlinking icq's are performed while holding both ioc and q
      70             :  *   locks.  Due to the lock ordering, q exit is simple but ioc exit
      71             :  *   requires reverse-order double lock dance.
      72             :  */
      73             : struct io_cq {
      74             :         struct request_queue    *q;
      75             :         struct io_context       *ioc;
      76             : 
      77             :         /*
      78             :          * q_node and ioc_node link io_cq through icq_list of q and ioc
      79             :          * respectively.  Both fields are unused once ioc_exit_icq() is
      80             :          * called and shared with __rcu_icq_cache and __rcu_head which are
      81             :          * used for RCU free of io_cq.
      82             :          */
      83             :         union {
      84             :                 struct list_head        q_node;
      85             :                 struct kmem_cache       *__rcu_icq_cache;
      86             :         };
      87             :         union {
      88             :                 struct hlist_node       ioc_node;
      89             :                 struct rcu_head         __rcu_head;
      90             :         };
      91             : 
      92             :         unsigned int            flags;
      93             : };
      94             : 
      95             : /*
      96             :  * I/O subsystem state of the associated processes.  It is refcounted
      97             :  * and kmalloc'ed. These could be shared between processes.
      98             :  */
      99             : struct io_context {
     100             :         atomic_long_t refcount;
     101             :         atomic_t active_ref;
     102             : 
     103             :         unsigned short ioprio;
     104             : 
     105             : #ifdef CONFIG_BLK_ICQ
     106             :         /* all the fields below are protected by this lock */
     107             :         spinlock_t lock;
     108             : 
     109             :         struct radix_tree_root  icq_tree;
     110             :         struct io_cq __rcu      *icq_hint;
     111             :         struct hlist_head       icq_list;
     112             : 
     113             :         struct work_struct release_work;
     114             : #endif /* CONFIG_BLK_ICQ */
     115             : };
     116             : 
     117             : struct task_struct;
     118             : #ifdef CONFIG_BLOCK
     119             : void put_io_context(struct io_context *ioc);
     120             : void exit_io_context(struct task_struct *task);
     121             : int __copy_io(unsigned long clone_flags, struct task_struct *tsk);
     122             : static inline int copy_io(unsigned long clone_flags, struct task_struct *tsk)
     123             : {
     124         175 :         if (!current->io_context)
     125             :                 return 0;
     126           0 :         return __copy_io(clone_flags, tsk);
     127             : }
     128             : #else
     129             : struct io_context;
     130             : static inline void put_io_context(struct io_context *ioc) { }
     131             : static inline void exit_io_context(struct task_struct *task) { }
     132             : static inline int copy_io(unsigned long clone_flags, struct task_struct *tsk)
     133             : {
     134             :         return 0;
     135             : }
     136             : #endif /* CONFIG_BLOCK */
     137             : 
     138             : #endif /* IOCONTEXT_H */