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TOMOYO Linux Cross Reference
Linux/block/blk-ioc.c

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  1 /*
  2  * Functions related to io context handling
  3  */
  4 #include <linux/kernel.h>
  5 #include <linux/module.h>
  6 #include <linux/init.h>
  7 #include <linux/bio.h>
  8 #include <linux/blkdev.h>
  9 #include <linux/bootmem.h>      /* for max_pfn/max_low_pfn */
 10 
 11 #include "blk.h"
 12 
 13 /*
 14  * For io context allocations
 15  */
 16 static struct kmem_cache *iocontext_cachep;
 17 
 18 static void cfq_dtor(struct io_context *ioc)
 19 {
 20         if (!hlist_empty(&ioc->cic_list)) {
 21                 struct cfq_io_context *cic;
 22 
 23                 cic = list_entry(ioc->cic_list.first, struct cfq_io_context,
 24                                                                 cic_list);
 25                 cic->dtor(ioc);
 26         }
 27 }
 28 
 29 /*
 30  * IO Context helper functions. put_io_context() returns 1 if there are no
 31  * more users of this io context, 0 otherwise.
 32  */
 33 int put_io_context(struct io_context *ioc)
 34 {
 35         if (ioc == NULL)
 36                 return 1;
 37 
 38         BUG_ON(atomic_long_read(&ioc->refcount) == 0);
 39 
 40         if (atomic_long_dec_and_test(&ioc->refcount)) {
 41                 rcu_read_lock();
 42                 if (ioc->aic && ioc->aic->dtor)
 43                         ioc->aic->dtor(ioc->aic);
 44                 cfq_dtor(ioc);
 45                 rcu_read_unlock();
 46 
 47                 kmem_cache_free(iocontext_cachep, ioc);
 48                 return 1;
 49         }
 50         return 0;
 51 }
 52 EXPORT_SYMBOL(put_io_context);
 53 
 54 static void cfq_exit(struct io_context *ioc)
 55 {
 56         rcu_read_lock();
 57 
 58         if (!hlist_empty(&ioc->cic_list)) {
 59                 struct cfq_io_context *cic;
 60 
 61                 cic = list_entry(ioc->cic_list.first, struct cfq_io_context,
 62                                                                 cic_list);
 63                 cic->exit(ioc);
 64         }
 65         rcu_read_unlock();
 66 }
 67 
 68 /* Called by the exitting task */
 69 void exit_io_context(struct task_struct *task)
 70 {
 71         struct io_context *ioc;
 72 
 73         task_lock(task);
 74         ioc = task->io_context;
 75         task->io_context = NULL;
 76         task_unlock(task);
 77 
 78         if (atomic_dec_and_test(&ioc->nr_tasks)) {
 79                 if (ioc->aic && ioc->aic->exit)
 80                         ioc->aic->exit(ioc->aic);
 81                 cfq_exit(ioc);
 82 
 83         }
 84         put_io_context(ioc);
 85 }
 86 
 87 struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
 88 {
 89         struct io_context *ret;
 90 
 91         ret = kmem_cache_alloc_node(iocontext_cachep, gfp_flags, node);
 92         if (ret) {
 93                 atomic_long_set(&ret->refcount, 1);
 94                 atomic_set(&ret->nr_tasks, 1);
 95                 spin_lock_init(&ret->lock);
 96                 ret->ioprio_changed = 0;
 97                 ret->ioprio = 0;
 98                 ret->last_waited = jiffies; /* doesn't matter... */
 99                 ret->nr_batch_requests = 0; /* because this is 0 */
100                 ret->aic = NULL;
101                 INIT_RADIX_TREE(&ret->radix_root, GFP_ATOMIC | __GFP_HIGH);
102                 INIT_HLIST_HEAD(&ret->cic_list);
103                 ret->ioc_data = NULL;
104         }
105 
106         return ret;
107 }
108 
109 /*
110  * If the current task has no IO context then create one and initialise it.
111  * Otherwise, return its existing IO context.
112  *
113  * This returned IO context doesn't have a specifically elevated refcount,
114  * but since the current task itself holds a reference, the context can be
115  * used in general code, so long as it stays within `current` context.
116  */
117 struct io_context *current_io_context(gfp_t gfp_flags, int node)
118 {
119         struct task_struct *tsk = current;
120         struct io_context *ret;
121 
122         ret = tsk->io_context;
123         if (likely(ret))
124                 return ret;
125 
126         ret = alloc_io_context(gfp_flags, node);
127         if (ret) {
128                 /* make sure set_task_ioprio() sees the settings above */
129                 smp_wmb();
130                 tsk->io_context = ret;
131         }
132 
133         return ret;
134 }
135 
136 /*
137  * If the current task has no IO context then create one and initialise it.
138  * If it does have a context, take a ref on it.
139  *
140  * This is always called in the context of the task which submitted the I/O.
141  */
142 struct io_context *get_io_context(gfp_t gfp_flags, int node)
143 {
144         struct io_context *ret = NULL;
145 
146         /*
147          * Check for unlikely race with exiting task. ioc ref count is
148          * zero when ioc is being detached.
149          */
150         do {
151                 ret = current_io_context(gfp_flags, node);
152                 if (unlikely(!ret))
153                         break;
154         } while (!atomic_long_inc_not_zero(&ret->refcount));
155 
156         return ret;
157 }
158 EXPORT_SYMBOL(get_io_context);
159 
160 void copy_io_context(struct io_context **pdst, struct io_context **psrc)
161 {
162         struct io_context *src = *psrc;
163         struct io_context *dst = *pdst;
164 
165         if (src) {
166                 BUG_ON(atomic_long_read(&src->refcount) == 0);
167                 atomic_long_inc(&src->refcount);
168                 put_io_context(dst);
169                 *pdst = src;
170         }
171 }
172 EXPORT_SYMBOL(copy_io_context);
173 
174 static int __init blk_ioc_init(void)
175 {
176         iocontext_cachep = kmem_cache_create("blkdev_ioc",
177                         sizeof(struct io_context), 0, SLAB_PANIC, NULL);
178         return 0;
179 }
180 subsys_initcall(blk_ioc_init);
181 

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