root/block/blk-ioc.c

DEFINITIONS

1. cfq_dtor
2. put_io_context
3. cfq_exit
4. exit_io_context
5. alloc_io_context
6. current_io_context
7. get_io_context
8. copy_io_context
9. blk_ioc_init

/*
 * Functions related to io context handling
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/bootmem.h>      /* for max_pfn/max_low_pfn */

#include "blk.h"

/*
 * For io context allocations
 */
static struct kmem_cache *iocontext_cachep;

static void cfq_dtor(struct io_context *ioc)
{
        if (!hlist_empty(&ioc->cic_list)) {
                struct cfq_io_context *cic;

                cic = list_entry(ioc->cic_list.first, struct cfq_io_context,
                                                                cic_list);
                cic->dtor(ioc);
        }
}

/*
 * IO Context helper functions. put_io_context() returns 1 if there are no
 * more users of this io context, 0 otherwise.
 */
int put_io_context(struct io_context *ioc)
{
        if (ioc == NULL)
                return 1;

        BUG_ON(atomic_read(&ioc->refcount) == 0);

        if (atomic_dec_and_test(&ioc->refcount)) {
                rcu_read_lock();
                if (ioc->aic && ioc->aic->dtor)
                        ioc->aic->dtor(ioc->aic);
                cfq_dtor(ioc);
                rcu_read_unlock();

                kmem_cache_free(iocontext_cachep, ioc);
                return 1;
        }
        return 0;
}
EXPORT_SYMBOL(put_io_context);

static void cfq_exit(struct io_context *ioc)
{
        rcu_read_lock();

        if (!hlist_empty(&ioc->cic_list)) {
                struct cfq_io_context *cic;

                cic = list_entry(ioc->cic_list.first, struct cfq_io_context,
                                                                cic_list);
                cic->exit(ioc);
        }
        rcu_read_unlock();
}

/* Called by the exitting task */
void exit_io_context(void)
{
        struct io_context *ioc;

        task_lock(current);
        ioc = current->io_context;
        current->io_context = NULL;
        task_unlock(current);

        if (atomic_dec_and_test(&ioc->nr_tasks)) {
                if (ioc->aic && ioc->aic->exit)
                        ioc->aic->exit(ioc->aic);
                cfq_exit(ioc);

                put_io_context(ioc);
        }
}

struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
{
        struct io_context *ret;

        ret = kmem_cache_alloc_node(iocontext_cachep, gfp_flags, node);
        if (ret) {
                atomic_set(&ret->refcount, 1);
                atomic_set(&ret->nr_tasks, 1);
                spin_lock_init(&ret->lock);
                ret->ioprio_changed = 0;
                ret->ioprio = 0;
                ret->last_waited = jiffies; /* doesn't matter... */
                ret->nr_batch_requests = 0; /* because this is 0 */
                ret->aic = NULL;
                INIT_RADIX_TREE(&ret->radix_root, GFP_ATOMIC | __GFP_HIGH);
                INIT_HLIST_HEAD(&ret->cic_list);
                ret->ioc_data = NULL;
        }

        return ret;
}

/*
 * If the current task has no IO context then create one and initialise it.
 * Otherwise, return its existing IO context.
 *
 * This returned IO context doesn't have a specifically elevated refcount,
 * but since the current task itself holds a reference, the context can be
 * used in general code, so long as it stays within `current` context.
 */
struct io_context *current_io_context(gfp_t gfp_flags, int node)
{
        struct task_struct *tsk = current;
        struct io_context *ret;

        ret = tsk->io_context;
        if (likely(ret))
                return ret;

        ret = alloc_io_context(gfp_flags, node);
        if (ret) {
                /* make sure set_task_ioprio() sees the settings above */
                smp_wmb();
                tsk->io_context = ret;
        }

        return ret;
}

/*
 * If the current task has no IO context then create one and initialise it.
 * If it does have a context, take a ref on it.
 *
 * This is always called in the context of the task which submitted the I/O.
 */
struct io_context *get_io_context(gfp_t gfp_flags, int node)
{
        struct io_context *ret = NULL;

        /*
         * Check for unlikely race with exiting task. ioc ref count is
         * zero when ioc is being detached.
         */
        do {
                ret = current_io_context(gfp_flags, node);
                if (unlikely(!ret))
                        break;
        } while (!atomic_inc_not_zero(&ret->refcount));

        return ret;
}
EXPORT_SYMBOL(get_io_context);

void copy_io_context(struct io_context **pdst, struct io_context **psrc)
{
        struct io_context *src = *psrc;
        struct io_context *dst = *pdst;

        if (src) {
                BUG_ON(atomic_read(&src->refcount) == 0);
                atomic_inc(&src->refcount);
                put_io_context(dst);
                *pdst = src;
        }
}
EXPORT_SYMBOL(copy_io_context);

static int __init blk_ioc_init(void)
{
        iocontext_cachep = kmem_cache_create("blkdev_ioc",
                        sizeof(struct io_context), 0, SLAB_PANIC, NULL);
        return 0;
}
subsys_initcall(blk_ioc_init);