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linux-2.6/include/linux/device-mapper.h
Kiyoshi Ueda cec47e3d4a dm: prepare for request based option 
This patch adds core functions for request-based dm.

When struct mapped device (md) is initialized, md->queue has
an I/O scheduler and the following functions are used for
request-based dm as the queue functions:
    make_request_fn: dm_make_request()
    pref_fn:         dm_prep_fn()
    request_fn:      dm_request_fn()
    softirq_done_fn: dm_softirq_done()
    lld_busy_fn:     dm_lld_busy()
Actual initializations are done in another patch (PATCH 2).

Below is a brief summary of how request-based dm behaves, including:
  - making request from bio
  - cloning, mapping and dispatching request
  - completing request and bio
  - suspending md
  - resuming md

  bio to request
  ==============
  md->queue->make_request_fn() (dm_make_request()) calls __make_request()
  for a bio submitted to the md.
  Then, the bio is kept in the queue as a new request or merged into
  another request in the queue if possible.

  Cloning and Mapping
  ===================
  Cloning and mapping are done in md->queue->request_fn() (dm_request_fn()),
  when requests are dispatched after they are sorted by the I/O scheduler.

  dm_request_fn() checks busy state of underlying devices using
  target's busy() function and stops dispatching requests to keep them
  on the dm device's queue if busy.
  It helps better I/O merging, since no merge is done for a request
  once it is dispatched to underlying devices.

  Actual cloning and mapping are done in dm_prep_fn() and map_request()
  called from dm_request_fn().
  dm_prep_fn() clones not only request but also bios of the request
  so that dm can hold bio completion in error cases and prevent
  the bio submitter from noticing the error.
  (See the "Completion" section below for details.)

  After the cloning, the clone is mapped by target's map_rq() function
    and inserted to underlying device's queue using
    blk_insert_cloned_request().

  Completion
  ==========
  Request completion can be hooked by rq->end_io(), but then, all bios
  in the request will have been completed even error cases, and the bio
  submitter will have noticed the error.
  To prevent the bio completion in error cases, request-based dm clones
  both bio and request and hooks both bio->bi_end_io() and rq->end_io():
      bio->bi_end_io(): end_clone_bio()
      rq->end_io():     end_clone_request()

  Summary of the request completion flow is below:
  blk_end_request() for a clone request
    => blk_update_request()
       => bio->bi_end_io() == end_clone_bio() for each clone bio
          => Free the clone bio
          => Success: Complete the original bio (blk_update_request())
             Error:   Don't complete the original bio
    => blk_finish_request()
       => rq->end_io() == end_clone_request()
          => blk_complete_request()
             => dm_softirq_done()
                => Free the clone request
                => Success: Complete the original request (blk_end_request())
                   Error:   Requeue the original request

  end_clone_bio() completes the original request on the size of
  the original bio in successful cases.
  Even if all bios in the original request are completed by that
  completion, the original request must not be completed yet to keep
  the ordering of request completion for the stacking.
  So end_clone_bio() uses blk_update_request() instead of
  blk_end_request().
  In error cases, end_clone_bio() doesn't complete the original bio.
  It just frees the cloned bio and gives over the error handling to
  end_clone_request().

  end_clone_request(), which is called with queue lock held, completes
  the clone request and the original request in a softirq context
  (dm_softirq_done()), which has no queue lock, to avoid a deadlock
  issue on submission of another request during the completion:
      - The submitted request may be mapped to the same device
      - Request submission requires queue lock, but the queue lock
        has been held by itself and it doesn't know that

  The clone request has no clone bio when dm_softirq_done() is called.
  So target drivers can't resubmit it again even error cases.
  Instead, they can ask dm core for requeueing and remapping
  the original request in that cases.

  suspend
  =======
  Request-based dm uses stopping md->queue as suspend of the md.
  For noflush suspend, just stops md->queue.

  For flush suspend, inserts a marker request to the tail of md->queue.
  And dispatches all requests in md->queue until the marker comes to
  the front of md->queue.  Then, stops dispatching request and waits
  for the all dispatched requests to complete.
  After that, completes the marker request, stops md->queue and
  wake up the waiter on the suspend queue, md->wait.

  resume
  ======
  Starts md->queue.

Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2009-06-22 10:12:35 +01:00

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/*
* Copyright (C) 2001 Sistina Software (UK) Limited.
* Copyright (C) 2004-2008 Red Hat, Inc. All rights reserved.
*
* This file is released under the LGPL.
*/
#ifndef _LINUX_DEVICE_MAPPER_H
#define _LINUX_DEVICE_MAPPER_H
#include <linux/bio.h>
#include <linux/blkdev.h>
struct dm_dev;
struct dm_target;
struct dm_table;
struct mapped_device;
struct bio_vec;
typedef enum { STATUSTYPE_INFO, STATUSTYPE_TABLE } status_type_t;
union map_info {
void *ptr;
unsigned long long ll;
unsigned flush_request;
};
/*
* In the constructor the target parameter will already have the
* table, type, begin and len fields filled in.
*/
typedef int (*dm_ctr_fn) (struct dm_target *target,
unsigned int argc, char **argv);
/*
* The destructor doesn't need to free the dm_target, just
* anything hidden ti->private.
*/
typedef void (*dm_dtr_fn) (struct dm_target *ti);
/*
* The map function must return:
* < 0: error
* = 0: The target will handle the io by resubmitting it later
* = 1: simple remap complete
* = 2: The target wants to push back the io
*/
typedef int (*dm_map_fn) (struct dm_target *ti, struct bio *bio,
union map_info *map_context);
typedef int (*dm_map_request_fn) (struct dm_target *ti, struct request *clone,
union map_info *map_context);
/*
* Returns:
* < 0 : error (currently ignored)
* 0 : ended successfully
* 1 : for some reason the io has still not completed (eg,
* multipath target might want to requeue a failed io).
* 2 : The target wants to push back the io
*/
typedef int (*dm_endio_fn) (struct dm_target *ti,
struct bio *bio, int error,
union map_info *map_context);
typedef int (*dm_request_endio_fn) (struct dm_target *ti,
struct request *clone, int error,
union map_info *map_context);
typedef void (*dm_flush_fn) (struct dm_target *ti);
typedef void (*dm_presuspend_fn) (struct dm_target *ti);
typedef void (*dm_postsuspend_fn) (struct dm_target *ti);
typedef int (*dm_preresume_fn) (struct dm_target *ti);
typedef void (*dm_resume_fn) (struct dm_target *ti);
typedef int (*dm_status_fn) (struct dm_target *ti, status_type_t status_type,
char *result, unsigned int maxlen);
typedef int (*dm_message_fn) (struct dm_target *ti, unsigned argc, char **argv);
typedef int (*dm_ioctl_fn) (struct dm_target *ti, unsigned int cmd,
unsigned long arg);
typedef int (*dm_merge_fn) (struct dm_target *ti, struct bvec_merge_data *bvm,
struct bio_vec *biovec, int max_size);
typedef int (*iterate_devices_callout_fn) (struct dm_target *ti,
struct dm_dev *dev,
sector_t physical_start,
void *data);
typedef int (*dm_iterate_devices_fn) (struct dm_target *ti,
iterate_devices_callout_fn fn,
void *data);
/*
* Returns:
* 0: The target can handle the next I/O immediately.
* 1: The target can't handle the next I/O immediately.
*/
typedef int (*dm_busy_fn) (struct dm_target *ti);
void dm_error(const char *message);
/*
* Combine device limits.
*/
int dm_set_device_limits(struct dm_target *ti, struct dm_dev *dev,
sector_t start, void *data);
struct dm_dev {
struct block_device *bdev;
fmode_t mode;
char name[16];
};
/*
* Constructors should call these functions to ensure destination devices
* are opened/closed correctly.
* FIXME: too many arguments.
*/
int dm_get_device(struct dm_target *ti, const char *path, sector_t start,
sector_t len, fmode_t mode, struct dm_dev **result);
void dm_put_device(struct dm_target *ti, struct dm_dev *d);
/*
* Information about a target type
*/
/*
* Target features
*/
struct target_type {
uint64_t features;
const char *name;
struct module *module;
unsigned version[3];
dm_ctr_fn ctr;
dm_dtr_fn dtr;
dm_map_fn map;
dm_map_request_fn map_rq;
dm_endio_fn end_io;
dm_request_endio_fn rq_end_io;
dm_flush_fn flush;
dm_presuspend_fn presuspend;
dm_postsuspend_fn postsuspend;
dm_preresume_fn preresume;
dm_resume_fn resume;
dm_status_fn status;
dm_message_fn message;
dm_ioctl_fn ioctl;
dm_merge_fn merge;
dm_busy_fn busy;
dm_iterate_devices_fn iterate_devices;
/* For internal device-mapper use. */
struct list_head list;
};
struct dm_target {
struct dm_table *table;
struct target_type *type;
/* target limits */
sector_t begin;
sector_t len;
/* Always a power of 2 */
sector_t split_io;
/*
* A number of zero-length barrier requests that will be submitted
* to the target for the purpose of flushing cache.
*
* The request number will be placed in union map_info->flush_request.
* It is a responsibility of the target driver to remap these requests
* to the real underlying devices.
*/
unsigned num_flush_requests;
/* target specific data */
void *private;
/* Used to provide an error string from the ctr */
char *error;
};
int dm_register_target(struct target_type *t);
void dm_unregister_target(struct target_type *t);
/*-----------------------------------------------------------------
* Functions for creating and manipulating mapped devices.
* Drop the reference with dm_put when you finish with the object.
*---------------------------------------------------------------*/
/*
* DM_ANY_MINOR chooses the next available minor number.
*/
#define DM_ANY_MINOR (-1)
int dm_create(int minor, struct mapped_device **md);
/*
* Reference counting for md.
*/
struct mapped_device *dm_get_md(dev_t dev);
void dm_get(struct mapped_device *md);
void dm_put(struct mapped_device *md);
/*
* An arbitrary pointer may be stored alongside a mapped device.
*/
void dm_set_mdptr(struct mapped_device *md, void *ptr);
void *dm_get_mdptr(struct mapped_device *md);
/*
* A device can still be used while suspended, but I/O is deferred.
*/
int dm_suspend(struct mapped_device *md, unsigned suspend_flags);
int dm_resume(struct mapped_device *md);
/*
* Event functions.
*/
uint32_t dm_get_event_nr(struct mapped_device *md);
int dm_wait_event(struct mapped_device *md, int event_nr);
uint32_t dm_next_uevent_seq(struct mapped_device *md);
void dm_uevent_add(struct mapped_device *md, struct list_head *elist);
/*
* Info functions.
*/
const char *dm_device_name(struct mapped_device *md);
int dm_copy_name_and_uuid(struct mapped_device *md, char *name, char *uuid);
struct gendisk *dm_disk(struct mapped_device *md);
int dm_suspended(struct mapped_device *md);
int dm_noflush_suspending(struct dm_target *ti);
union map_info *dm_get_mapinfo(struct bio *bio);
union map_info *dm_get_rq_mapinfo(struct request *rq);
/*
* Geometry functions.
*/
int dm_get_geometry(struct mapped_device *md, struct hd_geometry *geo);
int dm_set_geometry(struct mapped_device *md, struct hd_geometry *geo);
/*-----------------------------------------------------------------
* Functions for manipulating device-mapper tables.
*---------------------------------------------------------------*/
/*
* First create an empty table.
*/
int dm_table_create(struct dm_table **result, fmode_t mode,
unsigned num_targets, struct mapped_device *md);
/*
* Then call this once for each target.
*/
int dm_table_add_target(struct dm_table *t, const char *type,
sector_t start, sector_t len, char *params);
/*
* Finally call this to make the table ready for use.
*/
int dm_table_complete(struct dm_table *t);
/*
* Unplug all devices in a table.
*/
void dm_table_unplug_all(struct dm_table *t);
/*
* Table reference counting.
*/
struct dm_table *dm_get_table(struct mapped_device *md);
void dm_table_get(struct dm_table *t);
void dm_table_put(struct dm_table *t);
/*
* Queries
*/
sector_t dm_table_get_size(struct dm_table *t);
unsigned int dm_table_get_num_targets(struct dm_table *t);
fmode_t dm_table_get_mode(struct dm_table *t);
struct mapped_device *dm_table_get_md(struct dm_table *t);
/*
* Trigger an event.
*/
void dm_table_event(struct dm_table *t);
/*
* The device must be suspended before calling this method.
*/
int dm_swap_table(struct mapped_device *md, struct dm_table *t);
/*
* A wrapper around vmalloc.
*/
void *dm_vcalloc(unsigned long nmemb, unsigned long elem_size);
/*-----------------------------------------------------------------
* Macros.
*---------------------------------------------------------------*/
#define DM_NAME "device-mapper"
#define DMCRIT(f, arg...) \
printk(KERN_CRIT DM_NAME ": " DM_MSG_PREFIX ": " f "\n", ## arg)
#define DMERR(f, arg...) \
printk(KERN_ERR DM_NAME ": " DM_MSG_PREFIX ": " f "\n", ## arg)
#define DMERR_LIMIT(f, arg...) \
do { \
if (printk_ratelimit()) \
printk(KERN_ERR DM_NAME ": " DM_MSG_PREFIX ": " \
f "\n", ## arg); \
} while (0)
#define DMWARN(f, arg...) \
printk(KERN_WARNING DM_NAME ": " DM_MSG_PREFIX ": " f "\n", ## arg)
#define DMWARN_LIMIT(f, arg...) \
do { \
if (printk_ratelimit()) \
printk(KERN_WARNING DM_NAME ": " DM_MSG_PREFIX ": " \
f "\n", ## arg); \
} while (0)
#define DMINFO(f, arg...) \
printk(KERN_INFO DM_NAME ": " DM_MSG_PREFIX ": " f "\n", ## arg)
#define DMINFO_LIMIT(f, arg...) \
do { \
if (printk_ratelimit()) \
printk(KERN_INFO DM_NAME ": " DM_MSG_PREFIX ": " f \
"\n", ## arg); \
} while (0)
#ifdef CONFIG_DM_DEBUG
# define DMDEBUG(f, arg...) \
printk(KERN_DEBUG DM_NAME ": " DM_MSG_PREFIX " DEBUG: " f "\n", ## arg)
# define DMDEBUG_LIMIT(f, arg...) \
do { \
if (printk_ratelimit()) \
printk(KERN_DEBUG DM_NAME ": " DM_MSG_PREFIX ": " f \
"\n", ## arg); \
} while (0)
#else
# define DMDEBUG(f, arg...) do {} while (0)
# define DMDEBUG_LIMIT(f, arg...) do {} while (0)
#endif
#define DMEMIT(x...) sz += ((sz >= maxlen) ? \
0 : scnprintf(result + sz, maxlen - sz, x))
#define SECTOR_SHIFT 9
/*
* Definitions of return values from target end_io function.
*/
#define DM_ENDIO_INCOMPLETE 1
#define DM_ENDIO_REQUEUE 2
/*
* Definitions of return values from target map function.
*/
#define DM_MAPIO_SUBMITTED 0
#define DM_MAPIO_REMAPPED 1
#define DM_MAPIO_REQUEUE DM_ENDIO_REQUEUE
/*
* Ceiling(n / sz)
*/
#define dm_div_up(n, sz) (((n) + (sz) - 1) / (sz))
#define dm_sector_div_up(n, sz) ( \
{ \
sector_t _r = ((n) + (sz) - 1); \
sector_div(_r, (sz)); \
_r; \
} \
)
/*
* ceiling(n / size) * size
*/
#define dm_round_up(n, sz) (dm_div_up((n), (sz)) * (sz))
#define dm_array_too_big(fixed, obj, num) \
((num) > (UINT_MAX - (fixed)) / (obj))
static inline sector_t to_sector(unsigned long n)
{
return (n >> SECTOR_SHIFT);
}
static inline unsigned long to_bytes(sector_t n)
{
return (n << SECTOR_SHIFT);
}
/*-----------------------------------------------------------------
* Helper for block layer and dm core operations
*---------------------------------------------------------------*/
void dm_dispatch_request(struct request *rq);
void dm_requeue_unmapped_request(struct request *rq);
void dm_kill_unmapped_request(struct request *rq, int error);
int dm_underlying_device_busy(struct request_queue *q);
#endif /* _LINUX_DEVICE_MAPPER_H */
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