dm-kcopyd.c

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/*
 * 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 <linux/types.h>
#include <linux/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 <linux/device-mapper.h>
#include <linux/dm-kcopyd.h>

#include "dm.h"

#define SUB_JOB_SIZE    128
#define SPLIT_COUNT 8
#define MIN_JOBS    8
#define RESERVE_PAGES   (DIV_ROUND_UP(SUB_JOB_SIZE << SECTOR_SHIFT, PAGE_SIZE))

/*-----------------------------------------------------------------
 * Each kcopyd client has its own little pool of preallocated
 * pages for kcopyd io.
 *---------------------------------------------------------------*/
struct dm_kcopyd_client {
    struct page_list *pages;
    unsigned nr_reserved_pages;
    unsigned nr_free_pages;

    struct dm_io_client *io_client;

    wait_queue_head_t destroyq;
    atomic_t nr_jobs;

    mempool_t *job_pool;

    struct workqueue_struct *kcopyd_wq;
    struct work_struct kcopyd_work;

/*
 * 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.
 */
    spinlock_t job_lock;
    struct list_head complete_jobs;
    struct list_head io_jobs;
    struct list_head pages_jobs;
};

static struct page_list zero_page_list;

static void wake(struct dm_kcopyd_client *kc)
{
    queue_work(kc->kcopyd_wq, &kc->kcopyd_work);
}

/*
 * Obtain one page for the use of kcopyd.
 */
static struct page_list *alloc_pl(gfp_t gfp)
{
    struct page_list *pl;

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

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

    return pl;
}

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

/*
 * Add the provided pages to a client's free page list, releasing
 * back to the system any beyond the reserved_pages limit.
 */
static void kcopyd_put_pages(struct dm_kcopyd_client *kc, struct page_list *pl)
{
    struct page_list *next;

    do {
        next = pl->next;

        if (kc->nr_free_pages >= kc->nr_reserved_pages)
            free_pl(pl);
        else {
            pl->next = kc->pages;
            kc->pages = pl;
            kc->nr_free_pages++;
        }

        pl = next;
    } while (pl);
}

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

    *pages = NULL;

    do {
        pl = alloc_pl(__GFP_NOWARN | __GFP_NORETRY);
        if (unlikely(!pl)) {
            /* Use reserved pages */
            pl = kc->pages;
            if (unlikely(!pl))
                goto out_of_memory;
            kc->pages = pl->next;
            kc->nr_free_pages--;
        }
        pl->next = *pages;
        *pages = pl;
    } while (--nr);

    return 0;

out_of_memory:
    if (*pages)
        kcopyd_put_pages(kc, *pages);
    return -ENOMEM;
}

/*
 * 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;
    }
}

/*
 * Allocate and reserve nr_pages for the use of a specific client.
 */
static int client_reserve_pages(struct dm_kcopyd_client *kc, unsigned nr_pages)
{
    unsigned i;
    struct page_list *pl = NULL, *next;

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

    kc->nr_reserved_pages += nr_pages;
    kcopyd_put_pages(kc, pl);

    return 0;
}

static void client_free_pages(struct dm_kcopyd_client *kc)
{
    BUG_ON(kc->nr_free_pages != kc->nr_reserved_pages);
    drop_pages(kc->pages);
    kc->pages = NULL;
    kc->nr_free_pages = kc->nr_reserved_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 dm_kcopyd_client *kc;
    struct list_head list;
    unsigned long flags;

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

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

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

    struct page_list *pages;

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

    struct kcopyd_job *master_job;
};

static struct kmem_cache *_job_cache;

int __init dm_kcopyd_init(void)
{
    _job_cache = kmem_cache_create("kcopyd_job",
                sizeof(struct kcopyd_job) * (SPLIT_COUNT + 1),
                __alignof__(struct kcopyd_job), 0, NULL);
    if (!_job_cache)
        return -ENOMEM;

    zero_page_list.next = &zero_page_list;
    zero_page_list.page = ZERO_PAGE(0);

    return 0;
}

void dm_kcopyd_exit(void)
{
    kmem_cache_destroy(_job_cache);
    _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 dm_kcopyd_client *kc)
{
    struct kcopyd_job *job = NULL;
    unsigned long flags;

    spin_lock_irqsave(&kc->job_lock, flags);

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

    return job;
}

static void push(struct list_head *jobs, struct kcopyd_job *job)
{
    unsigned long flags;
    struct dm_kcopyd_client *kc = job->kc;

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


static void push_head(struct list_head *jobs, struct kcopyd_job *job)
{
    unsigned long flags;
    struct dm_kcopyd_client *kc = job->kc;

    spin_lock_irqsave(&kc->job_lock, flags);
    list_add(&job->list, jobs);
    spin_unlock_irqrestore(&kc->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 long write_err = job->write_err;
    dm_kcopyd_notify_fn fn = job->fn;
    struct dm_kcopyd_client *kc = job->kc;

    if (job->pages && job->pages != &zero_page_list)
        kcopyd_put_pages(kc, job->pages);
    /*
     * If this is the master job, the sub jobs have already
     * completed so we can free everything.
     */
    if (job->master_job == job)
        mempool_free(job, kc->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;
    struct dm_kcopyd_client *kc = job->kc;

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

        if (!test_bit(DM_KCOPYD_IGNORE_ERROR, &job->flags)) {
            push(&kc->complete_jobs, job);
            wake(kc);
            return;
        }
    }

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

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

    wake(kc);
}

/*
 * 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 = 0,
        .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;
    unsigned nr_pages = dm_div_up(job->dests[0].count, PAGE_SIZE >> 9);

    r = kcopyd_get_pages(job->kc, nr_pages, &job->pages);
    if (!r) {
        /* this job is ready for io */
        push(&job->kc->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, struct dm_kcopyd_client *kc,
            int (*fn) (struct kcopyd_job *))
{
    struct kcopyd_job *job;
    int r, count = 0;

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

        r = fn(job);

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

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

        count++;
    }

    return count;
}

/*
 * kcopyd does this every time it's woken up.
 */
static void do_work(struct work_struct *work)
{
    struct dm_kcopyd_client *kc = container_of(work,
                    struct dm_kcopyd_client, kcopyd_work);
    struct blk_plug plug;

    /*
     * 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.
     */
    blk_start_plug(&plug);
    process_jobs(&kc->complete_jobs, kc, run_complete_job);
    process_jobs(&kc->pages_jobs, kc, run_pages_job);
    process_jobs(&kc->io_jobs, kc, run_io_job);
    blk_finish_plug(&plug);
}

/*
 * 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)
{
    struct dm_kcopyd_client *kc = job->kc;
    atomic_inc(&kc->nr_jobs);
    if (unlikely(!job->source.count))
        push(&kc->complete_jobs, job);
    else if (job->pages == &zero_page_list)
        push(&kc->io_jobs, job);
    else
        push(&kc->pages_jobs, job);
    wake(kc);
}

static void segment_complete(int read_err, unsigned long write_err,
                 void *context)
{
    /* FIXME: tidy this function */
    sector_t progress = 0;
    sector_t count = 0;
    struct kcopyd_job *sub_job = (struct kcopyd_job *) context;
    struct kcopyd_job *job = sub_job->master_job;
    struct dm_kcopyd_client *kc = job->kc;

    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(DM_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;

        *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 = sub_job;
        dispatch_job(sub_job);

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

        /*
         * Queue the completion callback to the kcopyd thread.
         *
         * Some callers assume that all the completions are called
         * from a single thread and don't race with each other.
         *
         * We must not call the callback directly here because this
         * code may not be executing in the thread.
         */
        push(&kc->complete_jobs, job);
        wake(kc);
    }
}

/*
 * Create some sub jobs to share the work between them.
 */
static void split_job(struct kcopyd_job *master_job)
{
    int i;

    atomic_inc(&master_job->kc->nr_jobs);

    atomic_set(&master_job->sub_jobs, SPLIT_COUNT);
    for (i = 0; i < SPLIT_COUNT; i++) {
        master_job[i + 1].master_job = master_job;
        segment_complete(0, 0u, &master_job[i + 1]);
    }
}

int dm_kcopyd_copy(struct dm_kcopyd_client *kc, struct dm_io_region *from,
           unsigned int num_dests, struct dm_io_region *dests,
           unsigned int flags, dm_kcopyd_notify_fn fn, void *context)
{
    struct kcopyd_job *job;

    /*
     * Allocate an array of jobs consisting of one master job
     * followed by SPLIT_COUNT sub jobs.
     */
    job = mempool_alloc(kc->job_pool, GFP_NOIO);

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

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

    if (from) {
        job->source = *from;
        job->pages = NULL;
        job->rw = READ;
    } else {
        memset(&job->source, 0, sizeof job->source);
        job->source.count = job->dests[0].count;
        job->pages = &zero_page_list;
        job->rw = WRITE;
    }

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

    if (job->source.count <= SUB_JOB_SIZE)
        dispatch_job(job);
    else {
        mutex_init(&job->lock);
        job->progress = 0;
        split_job(job);
    }

    return 0;
}
EXPORT_SYMBOL(dm_kcopyd_copy);

int dm_kcopyd_zero(struct dm_kcopyd_client *kc,
           unsigned num_dests, struct dm_io_region *dests,
           unsigned flags, dm_kcopyd_notify_fn fn, void *context)
{
    return dm_kcopyd_copy(kc, NULL, num_dests, dests, flags, fn, context);
}
EXPORT_SYMBOL(dm_kcopyd_zero);

void *dm_kcopyd_prepare_callback(struct dm_kcopyd_client *kc,
                 dm_kcopyd_notify_fn fn, void *context)
{
    struct kcopyd_job *job;

    job = mempool_alloc(kc->job_pool, GFP_NOIO);

    memset(job, 0, sizeof(struct kcopyd_job));
    job->kc = kc;
    job->fn = fn;
    job->context = context;
    job->master_job = job;

    atomic_inc(&kc->nr_jobs);

    return job;
}
EXPORT_SYMBOL(dm_kcopyd_prepare_callback);

void dm_kcopyd_do_callback(void *j, int read_err, unsigned long write_err)
{
    struct kcopyd_job *job = j;
    struct dm_kcopyd_client *kc = job->kc;

    job->read_err = read_err;
    job->write_err = write_err;

    push(&kc->complete_jobs, job);
    wake(kc);
}
EXPORT_SYMBOL(dm_kcopyd_do_callback);

/*
 * 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  */

/*-----------------------------------------------------------------
 * Client setup
 *---------------------------------------------------------------*/
struct dm_kcopyd_client *dm_kcopyd_client_create(void)
{
    int r = -ENOMEM;
    struct dm_kcopyd_client *kc;

    kc = kmalloc(sizeof(*kc), GFP_KERNEL);
    if (!kc)
        return ERR_PTR(-ENOMEM);

    spin_lock_init(&kc->job_lock);
    INIT_LIST_HEAD(&kc->complete_jobs);
    INIT_LIST_HEAD(&kc->io_jobs);
    INIT_LIST_HEAD(&kc->pages_jobs);

    kc->job_pool = mempool_create_slab_pool(MIN_JOBS, _job_cache);
    if (!kc->job_pool)
        goto bad_slab;

    INIT_WORK(&kc->kcopyd_work, do_work);
    kc->kcopyd_wq = alloc_workqueue("kcopyd",
                    WQ_NON_REENTRANT | WQ_MEM_RECLAIM, 0);
    if (!kc->kcopyd_wq)
        goto bad_workqueue;

    kc->pages = NULL;
    kc->nr_reserved_pages = kc->nr_free_pages = 0;
    r = client_reserve_pages(kc, RESERVE_PAGES);
    if (r)
        goto bad_client_pages;

    kc->io_client = dm_io_client_create();
    if (IS_ERR(kc->io_client)) {
        r = PTR_ERR(kc->io_client);
        goto bad_io_client;
    }

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

    return kc;

bad_io_client:
    client_free_pages(kc);
bad_client_pages:
    destroy_workqueue(kc->kcopyd_wq);
bad_workqueue:
    mempool_destroy(kc->job_pool);
bad_slab:
    kfree(kc);

    return ERR_PTR(r);
}
EXPORT_SYMBOL(dm_kcopyd_client_create);

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

    BUG_ON(!list_empty(&kc->complete_jobs));
    BUG_ON(!list_empty(&kc->io_jobs));
    BUG_ON(!list_empty(&kc->pages_jobs));
    destroy_workqueue(kc->kcopyd_wq);
    dm_io_client_destroy(kc->io_client);
    client_free_pages(kc);
    mempool_destroy(kc->job_pool);
    kfree(kc);
}
EXPORT_SYMBOL(dm_kcopyd_client_destroy);