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153 lines
4.6 KiB
153 lines
4.6 KiB
/* SPDX-License-Identifier: GPL-2.0 */ |
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#ifndef IOCONTEXT_H |
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#define IOCONTEXT_H |
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#include <linux/radix-tree.h> |
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#include <linux/rcupdate.h> |
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#include <linux/workqueue.h> |
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enum { |
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ICQ_EXITED = 1 << 2, |
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ICQ_DESTROYED = 1 << 3, |
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}; |
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/* |
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* An io_cq (icq) is association between an io_context (ioc) and a |
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* request_queue (q). This is used by elevators which need to track |
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* information per ioc - q pair. |
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* |
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* Elevator can request use of icq by setting elevator_type->icq_size and |
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* ->icq_align. Both size and align must be larger than that of struct |
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* io_cq and elevator can use the tail area for private information. The |
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* recommended way to do this is defining a struct which contains io_cq as |
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* the first member followed by private members and using its size and |
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* align. For example, |
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* |
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* struct snail_io_cq { |
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* struct io_cq icq; |
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* int poke_snail; |
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* int feed_snail; |
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* }; |
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* |
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* struct elevator_type snail_elv_type { |
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* .ops = { ... }, |
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* .icq_size = sizeof(struct snail_io_cq), |
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* .icq_align = __alignof__(struct snail_io_cq), |
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* ... |
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* }; |
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* |
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* If icq_size is set, block core will manage icq's. All requests will |
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* have its ->elv.icq field set before elevator_ops->elevator_set_req_fn() |
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* is called and be holding a reference to the associated io_context. |
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* |
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* Whenever a new icq is created, elevator_ops->elevator_init_icq_fn() is |
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* called and, on destruction, ->elevator_exit_icq_fn(). Both functions |
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* are called with both the associated io_context and queue locks held. |
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* |
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* Elevator is allowed to lookup icq using ioc_lookup_icq() while holding |
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* queue lock but the returned icq is valid only until the queue lock is |
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* released. Elevators can not and should not try to create or destroy |
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* icq's. |
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* |
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* As icq's are linked from both ioc and q, the locking rules are a bit |
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* complex. |
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* |
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* - ioc lock nests inside q lock. |
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* |
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* - ioc->icq_list and icq->ioc_node are protected by ioc lock. |
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* q->icq_list and icq->q_node by q lock. |
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* |
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* - ioc->icq_tree and ioc->icq_hint are protected by ioc lock, while icq |
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* itself is protected by q lock. However, both the indexes and icq |
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* itself are also RCU managed and lookup can be performed holding only |
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* the q lock. |
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* |
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* - icq's are not reference counted. They are destroyed when either the |
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* ioc or q goes away. Each request with icq set holds an extra |
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* reference to ioc to ensure it stays until the request is completed. |
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* |
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* - Linking and unlinking icq's are performed while holding both ioc and q |
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* locks. Due to the lock ordering, q exit is simple but ioc exit |
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* requires reverse-order double lock dance. |
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*/ |
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struct io_cq { |
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struct request_queue *q; |
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struct io_context *ioc; |
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/* |
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* q_node and ioc_node link io_cq through icq_list of q and ioc |
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* respectively. Both fields are unused once ioc_exit_icq() is |
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* called and shared with __rcu_icq_cache and __rcu_head which are |
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* used for RCU free of io_cq. |
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*/ |
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union { |
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struct list_head q_node; |
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struct kmem_cache *__rcu_icq_cache; |
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}; |
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union { |
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struct hlist_node ioc_node; |
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struct rcu_head __rcu_head; |
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}; |
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unsigned int flags; |
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}; |
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/* |
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* I/O subsystem state of the associated processes. It is refcounted |
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* and kmalloc'ed. These could be shared between processes. |
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*/ |
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struct io_context { |
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atomic_long_t refcount; |
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atomic_t active_ref; |
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atomic_t nr_tasks; |
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/* all the fields below are protected by this lock */ |
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spinlock_t lock; |
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unsigned short ioprio; |
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struct radix_tree_root icq_tree; |
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struct io_cq __rcu *icq_hint; |
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struct hlist_head icq_list; |
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struct work_struct release_work; |
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}; |
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/** |
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* get_io_context_active - get active reference on ioc |
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* @ioc: ioc of interest |
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* |
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* Only iocs with active reference can issue new IOs. This function |
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* acquires an active reference on @ioc. The caller must already have an |
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* active reference on @ioc. |
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*/ |
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static inline void get_io_context_active(struct io_context *ioc) |
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{ |
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WARN_ON_ONCE(atomic_long_read(&ioc->refcount) <= 0); |
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WARN_ON_ONCE(atomic_read(&ioc->active_ref) <= 0); |
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atomic_long_inc(&ioc->refcount); |
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atomic_inc(&ioc->active_ref); |
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} |
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static inline void ioc_task_link(struct io_context *ioc) |
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{ |
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get_io_context_active(ioc); |
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WARN_ON_ONCE(atomic_read(&ioc->nr_tasks) <= 0); |
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atomic_inc(&ioc->nr_tasks); |
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} |
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struct task_struct; |
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#ifdef CONFIG_BLOCK |
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void put_io_context(struct io_context *ioc); |
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void put_io_context_active(struct io_context *ioc); |
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void exit_io_context(struct task_struct *task); |
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struct io_context *get_task_io_context(struct task_struct *task, |
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gfp_t gfp_flags, int node); |
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#else |
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struct io_context; |
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static inline void put_io_context(struct io_context *ioc) { } |
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static inline void exit_io_context(struct task_struct *task) { } |
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#endif |
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#endif
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