linux/block/blk-tag.c
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   1/*
   2 * Functions related to tagged command queuing
   3 */
   4#include <linux/kernel.h>
   5#include <linux/module.h>
   6#include <linux/bio.h>
   7#include <linux/blkdev.h>
   8
   9#include "blk.h"
  10
  11/**
  12 * blk_queue_find_tag - find a request by its tag and queue
  13 * @q:   The request queue for the device
  14 * @tag: The tag of the request
  15 *
  16 * Notes:
  17 *    Should be used when a device returns a tag and you want to match
  18 *    it with a request.
  19 *
  20 *    no locks need be held.
  21 **/
  22struct request *blk_queue_find_tag(struct request_queue *q, int tag)
  23{
  24        return blk_map_queue_find_tag(q->queue_tags, tag);
  25}
  26EXPORT_SYMBOL(blk_queue_find_tag);
  27
  28/**
  29 * __blk_free_tags - release a given set of tag maintenance info
  30 * @bqt:        the tag map to free
  31 *
  32 * Tries to free the specified @bqt.  Returns true if it was
  33 * actually freed and false if there are still references using it
  34 */
  35static int __blk_free_tags(struct blk_queue_tag *bqt)
  36{
  37        int retval;
  38
  39        retval = atomic_dec_and_test(&bqt->refcnt);
  40        if (retval) {
  41                BUG_ON(find_first_bit(bqt->tag_map, bqt->max_depth) <
  42                                                        bqt->max_depth);
  43
  44                kfree(bqt->tag_index);
  45                bqt->tag_index = NULL;
  46
  47                kfree(bqt->tag_map);
  48                bqt->tag_map = NULL;
  49
  50                kfree(bqt);
  51        }
  52
  53        return retval;
  54}
  55
  56/**
  57 * __blk_queue_free_tags - release tag maintenance info
  58 * @q:  the request queue for the device
  59 *
  60 *  Notes:
  61 *    blk_cleanup_queue() will take care of calling this function, if tagging
  62 *    has been used. So there's no need to call this directly.
  63 **/
  64void __blk_queue_free_tags(struct request_queue *q)
  65{
  66        struct blk_queue_tag *bqt = q->queue_tags;
  67
  68        if (!bqt)
  69                return;
  70
  71        __blk_free_tags(bqt);
  72
  73        q->queue_tags = NULL;
  74        queue_flag_clear_unlocked(QUEUE_FLAG_QUEUED, q);
  75}
  76
  77/**
  78 * blk_free_tags - release a given set of tag maintenance info
  79 * @bqt:        the tag map to free
  80 *
  81 * For externally managed @bqt frees the map.  Callers of this
  82 * function must guarantee to have released all the queues that
  83 * might have been using this tag map.
  84 */
  85void blk_free_tags(struct blk_queue_tag *bqt)
  86{
  87        if (unlikely(!__blk_free_tags(bqt)))
  88                BUG();
  89}
  90EXPORT_SYMBOL(blk_free_tags);
  91
  92/**
  93 * blk_queue_free_tags - release tag maintenance info
  94 * @q:  the request queue for the device
  95 *
  96 *  Notes:
  97 *      This is used to disable tagged queuing to a device, yet leave
  98 *      queue in function.
  99 **/
 100void blk_queue_free_tags(struct request_queue *q)
 101{
 102        queue_flag_clear_unlocked(QUEUE_FLAG_QUEUED, q);
 103}
 104EXPORT_SYMBOL(blk_queue_free_tags);
 105
 106static int
 107init_tag_map(struct request_queue *q, struct blk_queue_tag *tags, int depth)
 108{
 109        struct request **tag_index;
 110        unsigned long *tag_map;
 111        int nr_ulongs;
 112
 113        if (q && depth > q->nr_requests * 2) {
 114                depth = q->nr_requests * 2;
 115                printk(KERN_ERR "%s: adjusted depth to %d\n",
 116                       __func__, depth);
 117        }
 118
 119        tag_index = kzalloc(depth * sizeof(struct request *), GFP_ATOMIC);
 120        if (!tag_index)
 121                goto fail;
 122
 123        nr_ulongs = ALIGN(depth, BITS_PER_LONG) / BITS_PER_LONG;
 124        tag_map = kzalloc(nr_ulongs * sizeof(unsigned long), GFP_ATOMIC);
 125        if (!tag_map)
 126                goto fail;
 127
 128        tags->real_max_depth = depth;
 129        tags->max_depth = depth;
 130        tags->tag_index = tag_index;
 131        tags->tag_map = tag_map;
 132
 133        return 0;
 134fail:
 135        kfree(tag_index);
 136        return -ENOMEM;
 137}
 138
 139static struct blk_queue_tag *__blk_queue_init_tags(struct request_queue *q,
 140                                                   int depth)
 141{
 142        struct blk_queue_tag *tags;
 143
 144        tags = kmalloc(sizeof(struct blk_queue_tag), GFP_ATOMIC);
 145        if (!tags)
 146                goto fail;
 147
 148        if (init_tag_map(q, tags, depth))
 149                goto fail;
 150
 151        atomic_set(&tags->refcnt, 1);
 152        return tags;
 153fail:
 154        kfree(tags);
 155        return NULL;
 156}
 157
 158/**
 159 * blk_init_tags - initialize the tag info for an external tag map
 160 * @depth:      the maximum queue depth supported
 161 **/
 162struct blk_queue_tag *blk_init_tags(int depth)
 163{
 164        return __blk_queue_init_tags(NULL, depth);
 165}
 166EXPORT_SYMBOL(blk_init_tags);
 167
 168/**
 169 * blk_queue_init_tags - initialize the queue tag info
 170 * @q:  the request queue for the device
 171 * @depth:  the maximum queue depth supported
 172 * @tags: the tag to use
 173 *
 174 * Queue lock must be held here if the function is called to resize an
 175 * existing map.
 176 **/
 177int blk_queue_init_tags(struct request_queue *q, int depth,
 178                        struct blk_queue_tag *tags)
 179{
 180        int rc;
 181
 182        BUG_ON(tags && q->queue_tags && tags != q->queue_tags);
 183
 184        if (!tags && !q->queue_tags) {
 185                tags = __blk_queue_init_tags(q, depth);
 186
 187                if (!tags)
 188                        goto fail;
 189        } else if (q->queue_tags) {
 190                rc = blk_queue_resize_tags(q, depth);
 191                if (rc)
 192                        return rc;
 193                queue_flag_set(QUEUE_FLAG_QUEUED, q);
 194                return 0;
 195        } else
 196                atomic_inc(&tags->refcnt);
 197
 198        /*
 199         * assign it, all done
 200         */
 201        q->queue_tags = tags;
 202        queue_flag_set_unlocked(QUEUE_FLAG_QUEUED, q);
 203        INIT_LIST_HEAD(&q->tag_busy_list);
 204        return 0;
 205fail:
 206        kfree(tags);
 207        return -ENOMEM;
 208}
 209EXPORT_SYMBOL(blk_queue_init_tags);
 210
 211/**
 212 * blk_queue_resize_tags - change the queueing depth
 213 * @q:  the request queue for the device
 214 * @new_depth: the new max command queueing depth
 215 *
 216 *  Notes:
 217 *    Must be called with the queue lock held.
 218 **/
 219int blk_queue_resize_tags(struct request_queue *q, int new_depth)
 220{
 221        struct blk_queue_tag *bqt = q->queue_tags;
 222        struct request **tag_index;
 223        unsigned long *tag_map;
 224        int max_depth, nr_ulongs;
 225
 226        if (!bqt)
 227                return -ENXIO;
 228
 229        /*
 230         * if we already have large enough real_max_depth.  just
 231         * adjust max_depth.  *NOTE* as requests with tag value
 232         * between new_depth and real_max_depth can be in-flight, tag
 233         * map can not be shrunk blindly here.
 234         */
 235        if (new_depth <= bqt->real_max_depth) {
 236                bqt->max_depth = new_depth;
 237                return 0;
 238        }
 239
 240        /*
 241         * Currently cannot replace a shared tag map with a new
 242         * one, so error out if this is the case
 243         */
 244        if (atomic_read(&bqt->refcnt) != 1)
 245                return -EBUSY;
 246
 247        /*
 248         * save the old state info, so we can copy it back
 249         */
 250        tag_index = bqt->tag_index;
 251        tag_map = bqt->tag_map;
 252        max_depth = bqt->real_max_depth;
 253
 254        if (init_tag_map(q, bqt, new_depth))
 255                return -ENOMEM;
 256
 257        memcpy(bqt->tag_index, tag_index, max_depth * sizeof(struct request *));
 258        nr_ulongs = ALIGN(max_depth, BITS_PER_LONG) / BITS_PER_LONG;
 259        memcpy(bqt->tag_map, tag_map, nr_ulongs * sizeof(unsigned long));
 260
 261        kfree(tag_index);
 262        kfree(tag_map);
 263        return 0;
 264}
 265EXPORT_SYMBOL(blk_queue_resize_tags);
 266
 267/**
 268 * blk_queue_end_tag - end tag operations for a request
 269 * @q:  the request queue for the device
 270 * @rq: the request that has completed
 271 *
 272 *  Description:
 273 *    Typically called when end_that_request_first() returns %0, meaning
 274 *    all transfers have been done for a request. It's important to call
 275 *    this function before end_that_request_last(), as that will put the
 276 *    request back on the free list thus corrupting the internal tag list.
 277 *
 278 *  Notes:
 279 *   queue lock must be held.
 280 **/
 281void blk_queue_end_tag(struct request_queue *q, struct request *rq)
 282{
 283        struct blk_queue_tag *bqt = q->queue_tags;
 284        int tag = rq->tag;
 285
 286        BUG_ON(tag == -1);
 287
 288        if (unlikely(tag >= bqt->real_max_depth))
 289                /*
 290                 * This can happen after tag depth has been reduced.
 291                 * FIXME: how about a warning or info message here?
 292                 */
 293                return;
 294
 295        list_del_init(&rq->queuelist);
 296        rq->cmd_flags &= ~REQ_QUEUED;
 297        rq->tag = -1;
 298
 299        if (unlikely(bqt->tag_index[tag] == NULL))
 300                printk(KERN_ERR "%s: tag %d is missing\n",
 301                       __func__, tag);
 302
 303        bqt->tag_index[tag] = NULL;
 304
 305        if (unlikely(!test_bit(tag, bqt->tag_map))) {
 306                printk(KERN_ERR "%s: attempt to clear non-busy tag (%d)\n",
 307                       __func__, tag);
 308                return;
 309        }
 310        /*
 311         * The tag_map bit acts as a lock for tag_index[bit], so we need
 312         * unlock memory barrier semantics.
 313         */
 314        clear_bit_unlock(tag, bqt->tag_map);
 315}
 316EXPORT_SYMBOL(blk_queue_end_tag);
 317
 318/**
 319 * blk_queue_start_tag - find a free tag and assign it
 320 * @q:  the request queue for the device
 321 * @rq:  the block request that needs tagging
 322 *
 323 *  Description:
 324 *    This can either be used as a stand-alone helper, or possibly be
 325 *    assigned as the queue &prep_rq_fn (in which case &struct request
 326 *    automagically gets a tag assigned). Note that this function
 327 *    assumes that any type of request can be queued! if this is not
 328 *    true for your device, you must check the request type before
 329 *    calling this function.  The request will also be removed from
 330 *    the request queue, so it's the drivers responsibility to readd
 331 *    it if it should need to be restarted for some reason.
 332 *
 333 *  Notes:
 334 *   queue lock must be held.
 335 **/
 336int blk_queue_start_tag(struct request_queue *q, struct request *rq)
 337{
 338        struct blk_queue_tag *bqt = q->queue_tags;
 339        unsigned max_depth, offset;
 340        int tag;
 341
 342        if (unlikely((rq->cmd_flags & REQ_QUEUED))) {
 343                printk(KERN_ERR
 344                       "%s: request %p for device [%s] already tagged %d",
 345                       __func__, rq,
 346                       rq->rq_disk ? rq->rq_disk->disk_name : "?", rq->tag);
 347                BUG();
 348        }
 349
 350        /*
 351         * Protect against shared tag maps, as we may not have exclusive
 352         * access to the tag map.
 353         *
 354         * We reserve a few tags just for sync IO, since we don't want
 355         * to starve sync IO on behalf of flooding async IO.
 356         */
 357        max_depth = bqt->max_depth;
 358        if (rq_is_sync(rq))
 359                offset = 0;
 360        else
 361                offset = max_depth >> 2;
 362
 363        do {
 364                tag = find_next_zero_bit(bqt->tag_map, max_depth, offset);
 365                if (tag >= max_depth)
 366                        return 1;
 367
 368        } while (test_and_set_bit_lock(tag, bqt->tag_map));
 369        /*
 370         * We need lock ordering semantics given by test_and_set_bit_lock.
 371         * See blk_queue_end_tag for details.
 372         */
 373
 374        rq->cmd_flags |= REQ_QUEUED;
 375        rq->tag = tag;
 376        bqt->tag_index[tag] = rq;
 377        blkdev_dequeue_request(rq);
 378        list_add(&rq->queuelist, &q->tag_busy_list);
 379        return 0;
 380}
 381EXPORT_SYMBOL(blk_queue_start_tag);
 382
 383/**
 384 * blk_queue_invalidate_tags - invalidate all pending tags
 385 * @q:  the request queue for the device
 386 *
 387 *  Description:
 388 *   Hardware conditions may dictate a need to stop all pending requests.
 389 *   In this case, we will safely clear the block side of the tag queue and
 390 *   readd all requests to the request queue in the right order.
 391 *
 392 *  Notes:
 393 *   queue lock must be held.
 394 **/
 395void blk_queue_invalidate_tags(struct request_queue *q)
 396{
 397        struct list_head *tmp, *n;
 398
 399        list_for_each_safe(tmp, n, &q->tag_busy_list)
 400                blk_requeue_request(q, list_entry_rq(tmp));
 401}
 402EXPORT_SYMBOL(blk_queue_invalidate_tags);
 403