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dm-io.c

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

#include "dm-io.h"

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

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

/* FIXME: can we shrink this ? */
struct io {
      unsigned long error;
      atomic_t count;
      struct task_struct *sleeper;
      struct dm_io_client *client;
      io_notify_fn callback;
      void *context;
};

/*
 * io contexts are only dynamically allocated for asynchronous
 * io.  Since async io is likely to be the majority of io we'll
 * have the same number of io contexts as bios! (FIXME: must reduce this).
 */

static unsigned int pages_to_ios(unsigned int pages)
{
      return 4 * pages; /* too many ? */
}

/*
 * Create a client with mempool and bioset.
 */
struct dm_io_client *dm_io_client_create(unsigned num_pages)
{
      unsigned ios = pages_to_ios(num_pages);
      struct dm_io_client *client;

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

      client->pool = mempool_create_kmalloc_pool(ios, sizeof(struct io));
      if (!client->pool)
            goto bad;

      client->bios = bioset_create(16, 16);
      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);

int dm_io_client_resize(unsigned num_pages, struct dm_io_client *client)
{
      return mempool_resize(client->pool, pages_to_ios(num_pages),
                        GFP_KERNEL);
}
EXPORT_SYMBOL(dm_io_client_resize);

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.
 * In order to save a memory allocation we store this the last
 * bvec which we know is unused (blech).
 * XXX This is ugly and can OOPS with some configs... find another way.
 *---------------------------------------------------------------*/
static inline void bio_set_region(struct bio *bio, unsigned region)
{
      bio->bi_io_vec[bio->bi_max_vecs].bv_len = region;
}

static inline unsigned bio_get_region(struct bio *bio)
{
      return bio->bi_io_vec[bio->bi_max_vecs].bv_len;
}

/*-----------------------------------------------------------------
 * 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);

      if (atomic_dec_and_test(&io->count)) {
            if (io->sleeper)
                  wake_up_process(io->sleeper);

            else {
                  int r = io->error;
                  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.
       */
      io = bio->bi_private;
      region = bio_get_region(bio);

      bio->bi_max_vecs++;
      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;
};

/*
 * 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;
}

static void dm_bio_destructor(struct bio *bio)
{
      struct io *io = bio->bi_private;

      bio_free(bio, io->client->bios);
}

/*
 * 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 int region, struct 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;

      while (remaining) {
            /*
             * Allocate a suitably sized-bio: we add an extra
             * bvec for bio_get/set_region() and decrement bi_max_vecs
             * to hide it from bio_add_page().
             */
            num_bvecs = dm_sector_div_up(remaining,
                                   (PAGE_SIZE >> SECTOR_SHIFT));
            num_bvecs = 1 + min_t(int, bio_get_nr_vecs(where->bdev),
                              num_bvecs);
            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;
            bio->bi_private = io;
            bio->bi_destructor = dm_bio_destructor;
            bio->bi_max_vecs--;
            bio_set_region(bio, region);

            /*
             * Try and add as many pages as possible.
             */
            while (remaining) {
                  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);
      }
}

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

      if (sync)
            rw |= (1 << BIO_RW_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)
                  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 io_region *where, int rw, struct dpages *dp,
               unsigned long *error_bits)
{
      struct io io;

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

      io.error = 0;
      atomic_set(&io.count, 1); /* see dispatch_io() */
      io.sleeper = current;
      io.client = client;

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

      while (1) {
            set_current_state(TASK_UNINTERRUPTIBLE);

            if (!atomic_read(&io.count) || signal_pending(current))
                  break;

            io_schedule();
      }
      set_current_state(TASK_RUNNING);

      if (atomic_read(&io.count))
            return -EINTR;

      if (error_bits)
            *error_bits = io.error;

      return io.error ? -EIO : 0;
}

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

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

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

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

static int dp_init(struct dm_io_request *io_req, struct dpages *dp)
{
      /* Set up dpages based on memory type */
      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:
            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
 */
int dm_io(struct dm_io_request *io_req, unsigned num_regions,
        struct io_region *where, unsigned long *sync_error_bits)
{
      int r;
      struct dpages dp;

      r = dp_init(io_req, &dp);
      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);

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