dm-io.c

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/*
 * Copyright (C) 2003 Sistina Software
 * Copyright (C) 2006 Red Hat GmbH
 *
 * This file is released under the GPL.
 */

#include "dm.h"

#include <linux/device-mapper.h>

#include <linux/bio.h>
#include <linux/mempool.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/dm-io.h>

#define DM_MSG_PREFIX "io"

#define DM_IO_MAX_REGIONS   BITS_PER_LONG
#define MIN_IOS     16
#define MIN_BIOS    16

struct dm_io_client {
    mempool_t *pool;
    struct bio_set *bios;
};

/*
 * Aligning 'struct io' reduces the number of bits required to store
 * its address.  Refer to store_io_and_region_in_bio() below.
 */
struct io {
    unsigned long error_bits;
    atomic_t count;
    struct task_struct *sleeper;
    struct dm_io_client *client;
    io_notify_fn callback;
    void *context;
    void *vma_invalidate_address;
    unsigned long vma_invalidate_size;
} __attribute__((aligned(DM_IO_MAX_REGIONS)));

static struct kmem_cache *_dm_io_cache;

/*
 * Create a client with mempool and bioset.
 */
struct dm_io_client *dm_io_client_create(void)
{
    struct dm_io_client *client;

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

    client->pool = mempool_create_slab_pool(MIN_IOS, _dm_io_cache);
    if (!client->pool)
        goto bad;

    client->bios = bioset_create(MIN_BIOS, 0);
    if (!client->bios)
        goto bad;

    return client;

   bad:
    if (client->pool)
        mempool_destroy(client->pool);
    kfree(client);
    return ERR_PTR(-ENOMEM);
}
EXPORT_SYMBOL(dm_io_client_create);

void dm_io_client_destroy(struct dm_io_client *client)
{
    mempool_destroy(client->pool);
    bioset_free(client->bios);
    kfree(client);
}
EXPORT_SYMBOL(dm_io_client_destroy);

/*-----------------------------------------------------------------
 * We need to keep track of which region a bio is doing io for.
 * To avoid a memory allocation to store just 5 or 6 bits, we
 * ensure the 'struct io' pointer is aligned so enough low bits are
 * always zero and then combine it with the region number directly in
 * bi_private.
 *---------------------------------------------------------------*/
static void store_io_and_region_in_bio(struct bio *bio, struct io *io,
                       unsigned region)
{
    if (unlikely(!IS_ALIGNED((unsigned long)io, DM_IO_MAX_REGIONS))) {
        DMCRIT("Unaligned struct io pointer %p", io);
        BUG();
    }

    bio->bi_private = (void *)((unsigned long)io | region);
}

static void retrieve_io_and_region_from_bio(struct bio *bio, struct io **io,
                       unsigned *region)
{
    unsigned long val = (unsigned long)bio->bi_private;

    *io = (void *)(val & -(unsigned long)DM_IO_MAX_REGIONS);
    *region = val & (DM_IO_MAX_REGIONS - 1);
}

/*-----------------------------------------------------------------
 * We need an io object to keep track of the number of bios that
 * have been dispatched for a particular io.
 *---------------------------------------------------------------*/
static void dec_count(struct io *io, unsigned int region, int error)
{
    if (error)
        set_bit(region, &io->error_bits);

    if (atomic_dec_and_test(&io->count)) {
        if (io->vma_invalidate_size)
            invalidate_kernel_vmap_range(io->vma_invalidate_address,
                             io->vma_invalidate_size);

        if (io->sleeper)
            wake_up_process(io->sleeper);

        else {
            unsigned long r = io->error_bits;
            io_notify_fn fn = io->callback;
            void *context = io->context;

            mempool_free(io, io->client->pool);
            fn(r, context);
        }
    }
}

static void endio(struct bio *bio, int error)
{
    struct io *io;
    unsigned region;

    if (error && bio_data_dir(bio) == READ)
        zero_fill_bio(bio);

    /*
     * The bio destructor in bio_put() may use the io object.
     */
    retrieve_io_and_region_from_bio(bio, &io, &region);

    bio_put(bio);

    dec_count(io, region, error);
}

/*-----------------------------------------------------------------
 * These little objects provide an abstraction for getting a new
 * destination page for io.
 *---------------------------------------------------------------*/
struct dpages {
    void (*get_page)(struct dpages *dp,
             struct page **p, unsigned long *len, unsigned *offset);
    void (*next_page)(struct dpages *dp);

    unsigned context_u;
    void *context_ptr;

    void *vma_invalidate_address;
    unsigned long vma_invalidate_size;
};

/*
 * Functions for getting the pages from a list.
 */
static void list_get_page(struct dpages *dp,
          struct page **p, unsigned long *len, unsigned *offset)
{
    unsigned o = dp->context_u;
    struct page_list *pl = (struct page_list *) dp->context_ptr;

    *p = pl->page;
    *len = PAGE_SIZE - o;
    *offset = o;
}

static void list_next_page(struct dpages *dp)
{
    struct page_list *pl = (struct page_list *) dp->context_ptr;
    dp->context_ptr = pl->next;
    dp->context_u = 0;
}

static void list_dp_init(struct dpages *dp, struct page_list *pl, unsigned offset)
{
    dp->get_page = list_get_page;
    dp->next_page = list_next_page;
    dp->context_u = offset;
    dp->context_ptr = pl;
}

/*
 * Functions for getting the pages from a bvec.
 */
static void bvec_get_page(struct dpages *dp,
          struct page **p, unsigned long *len, unsigned *offset)
{
    struct bio_vec *bvec = (struct bio_vec *) dp->context_ptr;
    *p = bvec->bv_page;
    *len = bvec->bv_len;
    *offset = bvec->bv_offset;
}

static void bvec_next_page(struct dpages *dp)
{
    struct bio_vec *bvec = (struct bio_vec *) dp->context_ptr;
    dp->context_ptr = bvec + 1;
}

static void bvec_dp_init(struct dpages *dp, struct bio_vec *bvec)
{
    dp->get_page = bvec_get_page;
    dp->next_page = bvec_next_page;
    dp->context_ptr = bvec;
}

/*
 * Functions for getting the pages from a VMA.
 */
static void vm_get_page(struct dpages *dp,
         struct page **p, unsigned long *len, unsigned *offset)
{
    *p = vmalloc_to_page(dp->context_ptr);
    *offset = dp->context_u;
    *len = PAGE_SIZE - dp->context_u;
}

static void vm_next_page(struct dpages *dp)
{
    dp->context_ptr += PAGE_SIZE - dp->context_u;
    dp->context_u = 0;
}

static void vm_dp_init(struct dpages *dp, void *data)
{
    dp->get_page = vm_get_page;
    dp->next_page = vm_next_page;
    dp->context_u = ((unsigned long) data) & (PAGE_SIZE - 1);
    dp->context_ptr = data;
}

/*
 * Functions for getting the pages from kernel memory.
 */
static void km_get_page(struct dpages *dp, struct page **p, unsigned long *len,
            unsigned *offset)
{
    *p = virt_to_page(dp->context_ptr);
    *offset = dp->context_u;
    *len = PAGE_SIZE - dp->context_u;
}

static void km_next_page(struct dpages *dp)
{
    dp->context_ptr += PAGE_SIZE - dp->context_u;
    dp->context_u = 0;
}

static void km_dp_init(struct dpages *dp, void *data)
{
    dp->get_page = km_get_page;
    dp->next_page = km_next_page;
    dp->context_u = ((unsigned long) data) & (PAGE_SIZE - 1);
    dp->context_ptr = data;
}

/*-----------------------------------------------------------------
 * IO routines that accept a list of pages.
 *---------------------------------------------------------------*/
static void do_region(int rw, unsigned region, struct dm_io_region *where,
              struct dpages *dp, struct io *io)
{
    struct bio *bio;
    struct page *page;
    unsigned long len;
    unsigned offset;
    unsigned num_bvecs;
    sector_t remaining = where->count;
    struct request_queue *q = bdev_get_queue(where->bdev);
    sector_t discard_sectors;

    /*
     * where->count may be zero if rw holds a flush and we need to
     * send a zero-sized flush.
     */
    do {
        /*
         * Allocate a suitably sized-bio.
         */
        if (rw & REQ_DISCARD)
            num_bvecs = 1;
        else
            num_bvecs = min_t(int, bio_get_nr_vecs(where->bdev),
                      dm_sector_div_up(remaining, (PAGE_SIZE >> SECTOR_SHIFT)));

        bio = bio_alloc_bioset(GFP_NOIO, num_bvecs, io->client->bios);
        bio->bi_sector = where->sector + (where->count - remaining);
        bio->bi_bdev = where->bdev;
        bio->bi_end_io = endio;
        store_io_and_region_in_bio(bio, io, region);

        if (rw & REQ_DISCARD) {
            discard_sectors = min_t(sector_t, q->limits.max_discard_sectors, remaining);
            bio->bi_size = discard_sectors << SECTOR_SHIFT;
            remaining -= discard_sectors;
        } else while (remaining) {
            /*
             * Try and add as many pages as possible.
             */
            dp->get_page(dp, &page, &len, &offset);
            len = min(len, to_bytes(remaining));
            if (!bio_add_page(bio, page, len, offset))
                break;

            offset = 0;
            remaining -= to_sector(len);
            dp->next_page(dp);
        }

        atomic_inc(&io->count);
        submit_bio(rw, bio);
    } while (remaining);
}

static void dispatch_io(int rw, unsigned int num_regions,
            struct dm_io_region *where, struct dpages *dp,
            struct io *io, int sync)
{
    int i;
    struct dpages old_pages = *dp;

    BUG_ON(num_regions > DM_IO_MAX_REGIONS);

    if (sync)
        rw |= REQ_SYNC;

    /*
     * For multiple regions we need to be careful to rewind
     * the dp object for each call to do_region.
     */
    for (i = 0; i < num_regions; i++) {
        *dp = old_pages;
        if (where[i].count || (rw & REQ_FLUSH))
            do_region(rw, i, where + i, dp, io);
    }

    /*
     * Drop the extra reference that we were holding to avoid
     * the io being completed too early.
     */
    dec_count(io, 0, 0);
}

static int sync_io(struct dm_io_client *client, unsigned int num_regions,
           struct dm_io_region *where, int rw, struct dpages *dp,
           unsigned long *error_bits)
{
    /*
     * gcc <= 4.3 can't do the alignment for stack variables, so we must
     * align it on our own.
     * volatile prevents the optimizer from removing or reusing
     * "io_" field from the stack frame (allowed in ANSI C).
     */
    volatile char io_[sizeof(struct io) + __alignof__(struct io) - 1];
    struct io *io = (struct io *)PTR_ALIGN(&io_, __alignof__(struct io));

    if (num_regions > 1 && (rw & RW_MASK) != WRITE) {
        WARN_ON(1);
        return -EIO;
    }

    io->error_bits = 0;
    atomic_set(&io->count, 1); /* see dispatch_io() */
    io->sleeper = current;
    io->client = client;

    io->vma_invalidate_address = dp->vma_invalidate_address;
    io->vma_invalidate_size = dp->vma_invalidate_size;

    dispatch_io(rw, num_regions, where, dp, io, 1);

    while (1) {
        set_current_state(TASK_UNINTERRUPTIBLE);

        if (!atomic_read(&io->count))
            break;

        io_schedule();
    }
    set_current_state(TASK_RUNNING);

    if (error_bits)
        *error_bits = io->error_bits;

    return io->error_bits ? -EIO : 0;
}

static int async_io(struct dm_io_client *client, unsigned int num_regions,
            struct dm_io_region *where, int rw, struct dpages *dp,
            io_notify_fn fn, void *context)
{
    struct io *io;

    if (num_regions > 1 && (rw & RW_MASK) != WRITE) {
        WARN_ON(1);
        fn(1, context);
        return -EIO;
    }

    io = mempool_alloc(client->pool, GFP_NOIO);
    io->error_bits = 0;
    atomic_set(&io->count, 1); /* see dispatch_io() */
    io->sleeper = NULL;
    io->client = client;
    io->callback = fn;
    io->context = context;

    io->vma_invalidate_address = dp->vma_invalidate_address;
    io->vma_invalidate_size = dp->vma_invalidate_size;

    dispatch_io(rw, num_regions, where, dp, io, 0);
    return 0;
}

static int dp_init(struct dm_io_request *io_req, struct dpages *dp,
           unsigned long size)
{
    /* Set up dpages based on memory type */

    dp->vma_invalidate_address = NULL;
    dp->vma_invalidate_size = 0;

    switch (io_req->mem.type) {
    case DM_IO_PAGE_LIST:
        list_dp_init(dp, io_req->mem.ptr.pl, io_req->mem.offset);
        break;

    case DM_IO_BVEC:
        bvec_dp_init(dp, io_req->mem.ptr.bvec);
        break;

    case DM_IO_VMA:
        flush_kernel_vmap_range(io_req->mem.ptr.vma, size);
        if ((io_req->bi_rw & RW_MASK) == READ) {
            dp->vma_invalidate_address = io_req->mem.ptr.vma;
            dp->vma_invalidate_size = size;
        }
        vm_dp_init(dp, io_req->mem.ptr.vma);
        break;

    case DM_IO_KMEM:
        km_dp_init(dp, io_req->mem.ptr.addr);
        break;

    default:
        return -EINVAL;
    }

    return 0;
}

/*
 * New collapsed (a)synchronous interface.
 *
 * If the IO is asynchronous (i.e. it has notify.fn), you must either unplug
 * the queue with blk_unplug() some time later or set REQ_SYNC in
io_req->bi_rw. If you fail to do one of these, the IO will be submitted to
 * the disk after q->unplug_delay, which defaults to 3ms in blk-settings.c.
 */
int dm_io(struct dm_io_request *io_req, unsigned num_regions,
      struct dm_io_region *where, unsigned long *sync_error_bits)
{
    int r;
    struct dpages dp;

    r = dp_init(io_req, &dp, (unsigned long)where->count << SECTOR_SHIFT);
    if (r)
        return r;

    if (!io_req->notify.fn)
        return sync_io(io_req->client, num_regions, where,
                   io_req->bi_rw, &dp, sync_error_bits);

    return async_io(io_req->client, num_regions, where, io_req->bi_rw,
            &dp, io_req->notify.fn, io_req->notify.context);
}
EXPORT_SYMBOL(dm_io);

int __init dm_io_init(void)
{
    _dm_io_cache = KMEM_CACHE(io, 0);
    if (!_dm_io_cache)
        return -ENOMEM;

    return 0;
}

void dm_io_exit(void)
{
    kmem_cache_destroy(_dm_io_cache);
    _dm_io_cache = NULL;
}