/*
 * Functions related to tagged command queuing
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/slab.h>

#include "blk.h"

/**
 * blk_queue_find_tag - find a request by its tag and queue
 * @q:   The request queue for the device
 * @tag: The tag of the request
 *
 * Notes:
 *    Should be used when a device returns a tag and you want to match
 *    it with a request.
 *
 *    no locks need be held.
 **/
struct request *blk_queue_find_tag(struct request_queue *q, int tag)
{
        return blk_map_queue_find_tag(q->queue_tags, tag);
}
EXPORT_SYMBOL(blk_queue_find_tag);

/**
 * __blk_free_tags - release a given set of tag maintenance info
 * @bqt:        the tag map to free
 *
 * Tries to free the specified @bqt.  Returns true if it was
 * actually freed and false if there are still references using it
 */
static int __blk_free_tags(struct blk_queue_tag *bqt)
{
        int retval;

        retval = atomic_dec_and_test(&bqt->refcnt);
        if (retval) {
                BUG_ON(find_first_bit(bqt->tag_map, bqt->max_depth) <
                                                        bqt->max_depth);

                kfree(bqt->tag_index);
                bqt->tag_index = NULL;

                kfree(bqt->tag_map);
                bqt->tag_map = NULL;

                kfree(bqt);
        }

        return retval;
}

/**
 * __blk_queue_free_tags - release tag maintenance info
 * @q:  the request queue for the device
 *
 *  Notes:
 *    blk_cleanup_queue() will take care of calling this function, if tagging
 *    has been used. So there's no need to call this directly.
 **/
void __blk_queue_free_tags(struct request_queue *q)
{
        struct blk_queue_tag *bqt = q->queue_tags;

        if (!bqt)
                return;

        __blk_free_tags(bqt);

        q->queue_tags = NULL;
        queue_flag_clear_unlocked(QUEUE_FLAG_QUEUED, q);
}

/**
 * blk_free_tags - release a given set of tag maintenance info
 * @bqt:        the tag map to free
 *
 * For externally managed @bqt frees the map.  Callers of this
 * function must guarantee to have released all the queues that
 * might have been using this tag map.
 */
void blk_free_tags(struct blk_queue_tag *bqt)
{
        if (unlikely(!__blk_free_tags(bqt)))
                BUG();
}
EXPORT_SYMBOL(blk_free_tags);

/**
 * blk_queue_free_tags - release tag maintenance info
 * @q:  the request queue for the device
 *
 *  Notes:
 *      This is used to disable tagged queuing to a device, yet leave
 *      queue in function.
 **/
void blk_queue_free_tags(struct request_queue *q)
{
        queue_flag_clear_unlocked(QUEUE_FLAG_QUEUED, q);
}
EXPORT_SYMBOL(blk_queue_free_tags);

static int
init_tag_map(struct request_queue *q, struct blk_queue_tag *tags, int depth)
{
        struct request **tag_index;
        unsigned long *tag_map;
        int nr_ulongs;

        if (q && depth > q->nr_requests * 2) {
                depth = q->nr_requests * 2;
                printk(KERN_ERR "%s: adjusted depth to %d\n",
                       __func__, depth);
        }

        tag_index = kzalloc(depth * sizeof(struct request *), GFP_ATOMIC);
        if (!tag_index)
                goto fail;

        nr_ulongs = ALIGN(depth, BITS_PER_LONG) / BITS_PER_LONG;
        tag_map = kzalloc(nr_ulongs * sizeof(unsigned long), GFP_ATOMIC);
        if (!tag_map)
                goto fail;

        tags->real_max_depth = depth;
        tags->max_depth = depth;
        tags->tag_index = tag_index;
        tags->tag_map = tag_map;

        return 0;
fail:
        kfree(tag_index);
        return -ENOMEM;
}

static struct blk_queue_tag *__blk_queue_init_tags(struct request_queue *q,
                                                   int depth)
{
        struct blk_queue_tag *tags;

        tags = kmalloc(sizeof(struct blk_queue_tag), GFP_ATOMIC);
        if (!tags)
                goto fail;

        if (init_tag_map(q, tags, depth))
                goto fail;

        atomic_set(&tags->refcnt, 1);
        return tags;
fail:
        kfree(tags);
        return NULL;
}

/**
 * blk_init_tags - initialize the tag info for an external tag map
 * @depth:      the maximum queue depth supported
 **/
struct blk_queue_tag *blk_init_tags(int depth)
{
        return __blk_queue_init_tags(NULL, depth);
}
EXPORT_SYMBOL(blk_init_tags);

/**
 * blk_queue_init_tags - initialize the queue tag info
 * @q:  the request queue for the device
 * @depth:  the maximum queue depth supported
 * @tags: the tag to use
 *
 * Queue lock must be held here if the function is called to resize an
 * existing map.
 **/
int blk_queue_init_tags(struct request_queue *q, int depth,
                        struct blk_queue_tag *tags)
{
        int rc;

        BUG_ON(tags && q->queue_tags && tags != q->queue_tags);

        if (!tags && !q->queue_tags) {
                tags = __blk_queue_init_tags(q, depth);

                if (!tags)
                        goto fail;
        } else if (q->queue_tags) {
                rc = blk_queue_resize_tags(q, depth);
                if (rc)
                        return rc;
                queue_flag_set(QUEUE_FLAG_QUEUED, q);
                return 0;
        } else
                atomic_inc(&tags->refcnt);

        /*
         * assign it, all done
         */
        q->queue_tags = tags;
        queue_flag_set_unlocked(QUEUE_FLAG_QUEUED, q);
        INIT_LIST_HEAD(&q->tag_busy_list);
        return 0;
fail:
        kfree(tags);
        return -ENOMEM;
}
EXPORT_SYMBOL(blk_queue_init_tags);

/**
 * blk_queue_resize_tags - change the queueing depth
 * @q:  the request queue for the device
 * @new_depth: the new max command queueing depth
 *
 *  Notes:
 *    Must be called with the queue lock held.
 **/
int blk_queue_resize_tags(struct request_queue *q, int new_depth)
{
        struct blk_queue_tag *bqt = q->queue_tags;
        struct request **tag_index;
        unsigned long *tag_map;
        int max_depth, nr_ulongs;

        if (!bqt)
                return -ENXIO;

        /*
         * if we already have large enough real_max_depth.  just
         * adjust max_depth.  *NOTE* as requests with tag value
         * between new_depth and real_max_depth can be in-flight, tag
         * map can not be shrunk blindly here.
         */
        if (new_depth <= bqt->real_max_depth) {
                bqt->max_depth = new_depth;
                return 0;
        }

        /*
         * Currently cannot replace a shared tag map with a new
         * one, so error out if this is the case
         */
        if (atomic_read(&bqt->refcnt) != 1)
                return -EBUSY;

        /*
         * save the old state info, so we can copy it back
         */
        tag_index = bqt->tag_index;
        tag_map = bqt->tag_map;
        max_depth = bqt->real_max_depth;

        if (init_tag_map(q, bqt, new_depth))
                return -ENOMEM;

        memcpy(bqt->tag_index, tag_index, max_depth * sizeof(struct request *));
        nr_ulongs = ALIGN(max_depth, BITS_PER_LONG) / BITS_PER_LONG;
        memcpy(bqt->tag_map, tag_map, nr_ulongs * sizeof(unsigned long));

        kfree(tag_index);
        kfree(tag_map);
        return 0;
}
EXPORT_SYMBOL(blk_queue_resize_tags);

/**
 * blk_queue_end_tag - end tag operations for a request
 * @q:  the request queue for the device
 * @rq: the request that has completed
 *
 *  Description:
 *    Typically called when end_that_request_first() returns %0, meaning
 *    all transfers have been done for a request. It's important to call
 *    this function before end_that_request_last(), as that will put the
 *    request back on the free list thus corrupting the internal tag list.
 *
 *  Notes:
 *   queue lock must be held.
 **/
void blk_queue_end_tag(struct request_queue *q, struct request *rq)
{
        struct blk_queue_tag *bqt = q->queue_tags;
        int tag = rq->tag;

        BUG_ON(tag == -1);

        if (unlikely(tag >= bqt->real_max_depth))
                /*
                 * This can happen after tag depth has been reduced.
                 * FIXME: how about a warning or info message here?
                 */
                return;

        list_del_init(&rq->queuelist);
        rq->cmd_flags &= ~REQ_QUEUED;
        rq->tag = -1;

        if (unlikely(bqt->tag_index[tag] == NULL))
                printk(KERN_ERR "%s: tag %d is missing\n",
                       __func__, tag);

        bqt->tag_index[tag] = NULL;

        if (unlikely(!test_bit(tag, bqt->tag_map))) {
                printk(KERN_ERR "%s: attempt to clear non-busy tag (%d)\n",
                       __func__, tag);
                return;
        }
        /*
         * The tag_map bit acts as a lock for tag_index[bit], so we need
         * unlock memory barrier semantics.
         */
        clear_bit_unlock(tag, bqt->tag_map);
}
EXPORT_SYMBOL(blk_queue_end_tag);

/**
 * blk_queue_start_tag - find a free tag and assign it
 * @q:  the request queue for the device
 * @rq:  the block request that needs tagging
 *
 *  Description:
 *    This can either be used as a stand-alone helper, or possibly be
 *    assigned as the queue &prep_rq_fn (in which case &struct request
 *    automagically gets a tag assigned). Note that this function
 *    assumes that any type of request can be queued! if this is not
 *    true for your device, you must check the request type before
 *    calling this function.  The request will also be removed from
 *    the request queue, so it's the drivers responsibility to readd
 *    it if it should need to be restarted for some reason.
 *
 *  Notes:
 *   queue lock must be held.
 **/
int blk_queue_start_tag(struct request_queue *q, struct request *rq)
{
        struct blk_queue_tag *bqt = q->queue_tags;
        unsigned max_depth;
        int tag;

        if (unlikely((rq->cmd_flags & REQ_QUEUED))) {
                printk(KERN_ERR
                       "%s: request %p for device [%s] already tagged %d",
                       __func__, rq,
                       rq->rq_disk ? rq->rq_disk->disk_name : "?", rq->tag);
                BUG();
        }

        /*
         * Protect against shared tag maps, as we may not have exclusive
         * access to the tag map.
         *
         * We reserve a few tags just for sync IO, since we don't want
         * to starve sync IO on behalf of flooding async IO.
         */
        max_depth = bqt->max_depth;
        if (!rq_is_sync(rq) && max_depth > 1) {
                max_depth -= 2;
                if (!max_depth)
                        max_depth = 1;
                if (q->in_flight[BLK_RW_ASYNC] > max_depth)
                        return 1;
        }

        do {
                tag = find_first_zero_bit(bqt->tag_map, max_depth);
                if (tag >= max_depth)
                        return 1;

        } while (test_and_set_bit_lock(tag, bqt->tag_map));
        /*
         * We need lock ordering semantics given by test_and_set_bit_lock.
         * See blk_queue_end_tag for details.
         */

        rq->cmd_flags |= REQ_QUEUED;
        rq->tag = tag;
        bqt->tag_index[tag] = rq;
        blk_start_request(rq);
        list_add(&rq->queuelist, &q->tag_busy_list);
        return 0;
}
EXPORT_SYMBOL(blk_queue_start_tag);

/**
 * blk_queue_invalidate_tags - invalidate all pending tags
 * @q:  the request queue for the device
 *
 *  Description:
 *   Hardware conditions may dictate a need to stop all pending requests.
 *   In this case, we will safely clear the block side of the tag queue and
 *   readd all requests to the request queue in the right order.
 *
 *  Notes:
 *   queue lock must be held.
 **/
void blk_queue_invalidate_tags(struct request_queue *q)
{
        struct list_head *tmp, *n;

        list_for_each_safe(tmp, n, &q->tag_busy_list)
                blk_requeue_request(q, list_entry_rq(tmp));
}
EXPORT_SYMBOL(blk_queue_invalidate_tags);