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kcopyd.c

/*
 * Copyright (C) 2002 Sistina Software (UK) Limited.
 * Copyright (C) 2006 Red Hat GmbH
 *
 * This file is released under the GPL.
 *
 * Kcopyd provides a simple interface for copying an area of one
 * block-device to one or more other block-devices, with an asynchronous
 * completion notification.
 */

#include <asm/types.h>
#include <asm/atomic.h>

#include <linux/blkdev.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/mempool.h>
#include <linux/module.h>
#include <linux/pagemap.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/workqueue.h>
#include <linux/mutex.h>

#include "kcopyd.h"

static struct workqueue_struct *_kcopyd_wq;
static struct work_struct _kcopyd_work;

static void wake(void)
{
      queue_work(_kcopyd_wq, &_kcopyd_work);
}

/*-----------------------------------------------------------------
 * Each kcopyd client has its own little pool of preallocated
 * pages for kcopyd io.
 *---------------------------------------------------------------*/
struct kcopyd_client {
      struct list_head list;

      spinlock_t lock;
      struct page_list *pages;
      unsigned int nr_pages;
      unsigned int nr_free_pages;

      struct dm_io_client *io_client;

      wait_queue_head_t destroyq;
      atomic_t nr_jobs;
};

static struct page_list *alloc_pl(void)
{
      struct page_list *pl;

      pl = kmalloc(sizeof(*pl), GFP_KERNEL);
      if (!pl)
            return NULL;

      pl->page = alloc_page(GFP_KERNEL);
      if (!pl->page) {
            kfree(pl);
            return NULL;
      }

      return pl;
}

static void free_pl(struct page_list *pl)
{
      __free_page(pl->page);
      kfree(pl);
}

static int kcopyd_get_pages(struct kcopyd_client *kc,
                      unsigned int nr, struct page_list **pages)
{
      struct page_list *pl;

      spin_lock(&kc->lock);
      if (kc->nr_free_pages < nr) {
            spin_unlock(&kc->lock);
            return -ENOMEM;
      }

      kc->nr_free_pages -= nr;
      for (*pages = pl = kc->pages; --nr; pl = pl->next)
            ;

      kc->pages = pl->next;
      pl->next = NULL;

      spin_unlock(&kc->lock);

      return 0;
}

static void kcopyd_put_pages(struct kcopyd_client *kc, struct page_list *pl)
{
      struct page_list *cursor;

      spin_lock(&kc->lock);
      for (cursor = pl; cursor->next; cursor = cursor->next)
            kc->nr_free_pages++;

      kc->nr_free_pages++;
      cursor->next = kc->pages;
      kc->pages = pl;
      spin_unlock(&kc->lock);
}

/*
 * These three functions resize the page pool.
 */
static void drop_pages(struct page_list *pl)
{
      struct page_list *next;

      while (pl) {
            next = pl->next;
            free_pl(pl);
            pl = next;
      }
}

static int client_alloc_pages(struct kcopyd_client *kc, unsigned int nr)
{
      unsigned int i;
      struct page_list *pl = NULL, *next;

      for (i = 0; i < nr; i++) {
            next = alloc_pl();
            if (!next) {
                  if (pl)
                        drop_pages(pl);
                  return -ENOMEM;
            }
            next->next = pl;
            pl = next;
      }

      kcopyd_put_pages(kc, pl);
      kc->nr_pages += nr;
      return 0;
}

static void client_free_pages(struct kcopyd_client *kc)
{
      BUG_ON(kc->nr_free_pages != kc->nr_pages);
      drop_pages(kc->pages);
      kc->pages = NULL;
      kc->nr_free_pages = kc->nr_pages = 0;
}

/*-----------------------------------------------------------------
 * kcopyd_jobs need to be allocated by the *clients* of kcopyd,
 * for this reason we use a mempool to prevent the client from
 * ever having to do io (which could cause a deadlock).
 *---------------------------------------------------------------*/
struct kcopyd_job {
      struct kcopyd_client *kc;
      struct list_head list;
      unsigned long flags;

      /*
       * Error state of the job.
       */
      int read_err;
      unsigned int write_err;

      /*
       * Either READ or WRITE
       */
      int rw;
      struct io_region source;

      /*
       * The destinations for the transfer.
       */
      unsigned int num_dests;
      struct io_region dests[KCOPYD_MAX_REGIONS];

      sector_t offset;
      unsigned int nr_pages;
      struct page_list *pages;

      /*
       * Set this to ensure you are notified when the job has
       * completed.  'context' is for callback to use.
       */
      kcopyd_notify_fn fn;
      void *context;

      /*
       * These fields are only used if the job has been split
       * into more manageable parts.
       */
      struct mutex lock;
      atomic_t sub_jobs;
      sector_t progress;
};

/* FIXME: this should scale with the number of pages */
#define MIN_JOBS 512

static struct kmem_cache *_job_cache;
static mempool_t *_job_pool;

/*
 * We maintain three lists of jobs:
 *
 * i)   jobs waiting for pages
 * ii)  jobs that have pages, and are waiting for the io to be issued.
 * iii) jobs that have completed.
 *
 * All three of these are protected by job_lock.
 */
static DEFINE_SPINLOCK(_job_lock);

static LIST_HEAD(_complete_jobs);
static LIST_HEAD(_io_jobs);
static LIST_HEAD(_pages_jobs);

static int jobs_init(void)
{
      _job_cache = KMEM_CACHE(kcopyd_job, 0);
      if (!_job_cache)
            return -ENOMEM;

      _job_pool = mempool_create_slab_pool(MIN_JOBS, _job_cache);
      if (!_job_pool) {
            kmem_cache_destroy(_job_cache);
            return -ENOMEM;
      }

      return 0;
}

static void jobs_exit(void)
{
      BUG_ON(!list_empty(&_complete_jobs));
      BUG_ON(!list_empty(&_io_jobs));
      BUG_ON(!list_empty(&_pages_jobs));

      mempool_destroy(_job_pool);
      kmem_cache_destroy(_job_cache);
      _job_pool = NULL;
      _job_cache = NULL;
}

/*
 * Functions to push and pop a job onto the head of a given job
 * list.
 */
static struct kcopyd_job *pop(struct list_head *jobs)
{
      struct kcopyd_job *job = NULL;
      unsigned long flags;

      spin_lock_irqsave(&_job_lock, flags);

      if (!list_empty(jobs)) {
            job = list_entry(jobs->next, struct kcopyd_job, list);
            list_del(&job->list);
      }
      spin_unlock_irqrestore(&_job_lock, flags);

      return job;
}

static void push(struct list_head *jobs, struct kcopyd_job *job)
{
      unsigned long flags;

      spin_lock_irqsave(&_job_lock, flags);
      list_add_tail(&job->list, jobs);
      spin_unlock_irqrestore(&_job_lock, flags);
}

/*
 * These three functions process 1 item from the corresponding
 * job list.
 *
 * They return:
 * < 0: error
 *   0: success
 * > 0: can't process yet.
 */
static int run_complete_job(struct kcopyd_job *job)
{
      void *context = job->context;
      int read_err = job->read_err;
      unsigned int write_err = job->write_err;
      kcopyd_notify_fn fn = job->fn;
      struct kcopyd_client *kc = job->kc;

      kcopyd_put_pages(kc, job->pages);
      mempool_free(job, _job_pool);
      fn(read_err, write_err, context);

      if (atomic_dec_and_test(&kc->nr_jobs))
            wake_up(&kc->destroyq);

      return 0;
}

static void complete_io(unsigned long error, void *context)
{
      struct kcopyd_job *job = (struct kcopyd_job *) context;

      if (error) {
            if (job->rw == WRITE)
                  job->write_err |= error;
            else
                  job->read_err = 1;

            if (!test_bit(KCOPYD_IGNORE_ERROR, &job->flags)) {
                  push(&_complete_jobs, job);
                  wake();
                  return;
            }
      }

      if (job->rw == WRITE)
            push(&_complete_jobs, job);

      else {
            job->rw = WRITE;
            push(&_io_jobs, job);
      }

      wake();
}

/*
 * Request io on as many buffer heads as we can currently get for
 * a particular job.
 */
static int run_io_job(struct kcopyd_job *job)
{
      int r;
      struct dm_io_request io_req = {
            .bi_rw = job->rw,
            .mem.type = DM_IO_PAGE_LIST,
            .mem.ptr.pl = job->pages,
            .mem.offset = job->offset,
            .notify.fn = complete_io,
            .notify.context = job,
            .client = job->kc->io_client,
      };

      if (job->rw == READ)
            r = dm_io(&io_req, 1, &job->source, NULL);
      else
            r = dm_io(&io_req, job->num_dests, job->dests, NULL);

      return r;
}

static int run_pages_job(struct kcopyd_job *job)
{
      int r;

      job->nr_pages = dm_div_up(job->dests[0].count + job->offset,
                          PAGE_SIZE >> 9);
      r = kcopyd_get_pages(job->kc, job->nr_pages, &job->pages);
      if (!r) {
            /* this job is ready for io */
            push(&_io_jobs, job);
            return 0;
      }

      if (r == -ENOMEM)
            /* can't complete now */
            return 1;

      return r;
}

/*
 * Run through a list for as long as possible.  Returns the count
 * of successful jobs.
 */
static int process_jobs(struct list_head *jobs, int (*fn) (struct kcopyd_job *))
{
      struct kcopyd_job *job;
      int r, count = 0;

      while ((job = pop(jobs))) {

            r = fn(job);

            if (r < 0) {
                  /* error this rogue job */
                  if (job->rw == WRITE)
                        job->write_err = (unsigned int) -1;
                  else
                        job->read_err = 1;
                  push(&_complete_jobs, job);
                  break;
            }

            if (r > 0) {
                  /*
                   * We couldn't service this job ATM, so
                   * push this job back onto the list.
                   */
                  push(jobs, job);
                  break;
            }

            count++;
      }

      return count;
}

/*
 * kcopyd does this every time it's woken up.
 */
static void do_work(struct work_struct *ignored)
{
      /*
       * The order that these are called is *very* important.
       * complete jobs can free some pages for pages jobs.
       * Pages jobs when successful will jump onto the io jobs
       * list.  io jobs call wake when they complete and it all
       * starts again.
       */
      process_jobs(&_complete_jobs, run_complete_job);
      process_jobs(&_pages_jobs, run_pages_job);
      process_jobs(&_io_jobs, run_io_job);
}

/*
 * If we are copying a small region we just dispatch a single job
 * to do the copy, otherwise the io has to be split up into many
 * jobs.
 */
static void dispatch_job(struct kcopyd_job *job)
{
      atomic_inc(&job->kc->nr_jobs);
      push(&_pages_jobs, job);
      wake();
}

#define SUB_JOB_SIZE 128
static void segment_complete(int read_err,
                       unsigned int write_err, void *context)
{
      /* FIXME: tidy this function */
      sector_t progress = 0;
      sector_t count = 0;
      struct kcopyd_job *job = (struct kcopyd_job *) context;

      mutex_lock(&job->lock);

      /* update the error */
      if (read_err)
            job->read_err = 1;

      if (write_err)
            job->write_err |= write_err;

      /*
       * Only dispatch more work if there hasn't been an error.
       */
      if ((!job->read_err && !job->write_err) ||
          test_bit(KCOPYD_IGNORE_ERROR, &job->flags)) {
            /* get the next chunk of work */
            progress = job->progress;
            count = job->source.count - progress;
            if (count) {
                  if (count > SUB_JOB_SIZE)
                        count = SUB_JOB_SIZE;

                  job->progress += count;
            }
      }
      mutex_unlock(&job->lock);

      if (count) {
            int i;
            struct kcopyd_job *sub_job = mempool_alloc(_job_pool, GFP_NOIO);

            *sub_job = *job;
            sub_job->source.sector += progress;
            sub_job->source.count = count;

            for (i = 0; i < job->num_dests; i++) {
                  sub_job->dests[i].sector += progress;
                  sub_job->dests[i].count = count;
            }

            sub_job->fn = segment_complete;
            sub_job->context = job;
            dispatch_job(sub_job);

      } else if (atomic_dec_and_test(&job->sub_jobs)) {

            /*
             * To avoid a race we must keep the job around
             * until after the notify function has completed.
             * Otherwise the client may try and stop the job
             * after we've completed.
             */
            job->fn(read_err, write_err, job->context);
            mempool_free(job, _job_pool);
      }
}

/*
 * Create some little jobs that will do the move between
 * them.
 */
#define SPLIT_COUNT 8
static void split_job(struct kcopyd_job *job)
{
      int i;

      atomic_set(&job->sub_jobs, SPLIT_COUNT);
      for (i = 0; i < SPLIT_COUNT; i++)
            segment_complete(0, 0u, job);
}

int kcopyd_copy(struct kcopyd_client *kc, struct io_region *from,
            unsigned int num_dests, struct io_region *dests,
            unsigned int flags, kcopyd_notify_fn fn, void *context)
{
      struct kcopyd_job *job;

      /*
       * Allocate a new job.
       */
      job = mempool_alloc(_job_pool, GFP_NOIO);

      /*
       * set up for the read.
       */
      job->kc = kc;
      job->flags = flags;
      job->read_err = 0;
      job->write_err = 0;
      job->rw = READ;

      job->source = *from;

      job->num_dests = num_dests;
      memcpy(&job->dests, dests, sizeof(*dests) * num_dests);

      job->offset = 0;
      job->nr_pages = 0;
      job->pages = NULL;

      job->fn = fn;
      job->context = context;

      if (job->source.count < SUB_JOB_SIZE)
            dispatch_job(job);

      else {
            mutex_init(&job->lock);
            job->progress = 0;
            split_job(job);
      }

      return 0;
}

/*
 * Cancels a kcopyd job, eg. someone might be deactivating a
 * mirror.
 */
#if 0
int kcopyd_cancel(struct kcopyd_job *job, int block)
{
      /* FIXME: finish */
      return -1;
}
#endif  /*  0  */

/*-----------------------------------------------------------------
 * Unit setup
 *---------------------------------------------------------------*/
static DEFINE_MUTEX(_client_lock);
static LIST_HEAD(_clients);

static void client_add(struct kcopyd_client *kc)
{
      mutex_lock(&_client_lock);
      list_add(&kc->list, &_clients);
      mutex_unlock(&_client_lock);
}

static void client_del(struct kcopyd_client *kc)
{
      mutex_lock(&_client_lock);
      list_del(&kc->list);
      mutex_unlock(&_client_lock);
}

static DEFINE_MUTEX(kcopyd_init_lock);
static int kcopyd_clients = 0;

static int kcopyd_init(void)
{
      int r;

      mutex_lock(&kcopyd_init_lock);

      if (kcopyd_clients) {
            /* Already initialized. */
            kcopyd_clients++;
            mutex_unlock(&kcopyd_init_lock);
            return 0;
      }

      r = jobs_init();
      if (r) {
            mutex_unlock(&kcopyd_init_lock);
            return r;
      }

      _kcopyd_wq = create_singlethread_workqueue("kcopyd");
      if (!_kcopyd_wq) {
            jobs_exit();
            mutex_unlock(&kcopyd_init_lock);
            return -ENOMEM;
      }

      kcopyd_clients++;
      INIT_WORK(&_kcopyd_work, do_work);
      mutex_unlock(&kcopyd_init_lock);
      return 0;
}

static void kcopyd_exit(void)
{
      mutex_lock(&kcopyd_init_lock);
      kcopyd_clients--;
      if (!kcopyd_clients) {
            jobs_exit();
            destroy_workqueue(_kcopyd_wq);
            _kcopyd_wq = NULL;
      }
      mutex_unlock(&kcopyd_init_lock);
}

int kcopyd_client_create(unsigned int nr_pages, struct kcopyd_client **result)
{
      int r = 0;
      struct kcopyd_client *kc;

      r = kcopyd_init();
      if (r)
            return r;

      kc = kmalloc(sizeof(*kc), GFP_KERNEL);
      if (!kc) {
            kcopyd_exit();
            return -ENOMEM;
      }

      spin_lock_init(&kc->lock);
      kc->pages = NULL;
      kc->nr_pages = kc->nr_free_pages = 0;
      r = client_alloc_pages(kc, nr_pages);
      if (r) {
            kfree(kc);
            kcopyd_exit();
            return r;
      }

      kc->io_client = dm_io_client_create(nr_pages);
      if (IS_ERR(kc->io_client)) {
            r = PTR_ERR(kc->io_client);
            client_free_pages(kc);
            kfree(kc);
            kcopyd_exit();
            return r;
      }

      init_waitqueue_head(&kc->destroyq);
      atomic_set(&kc->nr_jobs, 0);

      client_add(kc);
      *result = kc;
      return 0;
}

void kcopyd_client_destroy(struct kcopyd_client *kc)
{
      /* Wait for completion of all jobs submitted by this client. */
      wait_event(kc->destroyq, !atomic_read(&kc->nr_jobs));

      dm_io_client_destroy(kc->io_client);
      client_free_pages(kc);
      client_del(kc);
      kfree(kc);
      kcopyd_exit();
}

EXPORT_SYMBOL(kcopyd_client_create);
EXPORT_SYMBOL(kcopyd_client_destroy);
EXPORT_SYMBOL(kcopyd_copy);

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