Linux v2.6.18-rc5

[pohmelfs.git] / drivers / md / kcopyd.c

/*
 * Copyright (C) 2002 Sistina Software (UK) Limited.
 *
 * 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 inline 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;

        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 semaphore lock;
        atomic_t sub_jobs;
        sector_t progress;
};

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

static kmem_cache_t *_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_create("kcopyd-jobs",
                                       sizeof(struct kcopyd_job),
                                       __alignof__(struct kcopyd_job),
                                       0, NULL, NULL);
        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 inline 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 inline 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;

        if (job->rw == READ)
                r = dm_io_async(1, &job->source, job->rw,
                                job->pages,
                                job->offset, complete_io, job);

        else
                r = dm_io_async(job->num_dests, job->dests, job->rw,
                                job->pages,
                                job->offset, complete_io, job);

        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(void *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;

        down(&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;
                }
        }
        up(&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 {
                init_MUTEX(&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, NULL);
        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;
        }

        r = dm_io_get(nr_pages);
        if (r) {
                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_put(kc->nr_pages);
        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);