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/*
* dm-snapshot.c
*
* Copyright (C) 2001-2002 Sistina Software (UK) Limited.
*
* This file is released under the GPL.
*/
#include <linux/blkdev.h>
#include <linux/device-mapper.h>
#include <linux/delay.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kdev_t.h>
#include <linux/list.h>
#include <linux/mempool.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/log2.h>
#include <linux/dm-kcopyd.h>
#include "dm.h"
#include "dm-exception-store.h"
#define DM_MSG_PREFIX "snapshots"
static const char dm_snapshot_merge_target_name[] = "snapshot-merge";
#define dm_target_is_snapshot_merge(ti) \
((ti)->type->name == dm_snapshot_merge_target_name)
/*
* The size of the mempool used to track chunks in use.
*/
#define MIN_IOS 256
#define DM_TRACKED_CHUNK_HASH_SIZE 16
#define DM_TRACKED_CHUNK_HASH(x) ((unsigned long)(x) & \
(DM_TRACKED_CHUNK_HASH_SIZE - 1))
struct dm_exception_table {
uint32_t hash_mask;
unsigned hash_shift;
struct list_head *table;
};
struct dm_snapshot {
struct rw_semaphore lock;
struct dm_dev *origin;
struct dm_dev *cow;
struct dm_target *ti;
/* List of snapshots per Origin */
struct list_head list;
/*
* You can't use a snapshot if this is 0 (e.g. if full).
* A snapshot-merge target never clears this.
*/
int valid;
/*
* The snapshot overflowed because of a write to the snapshot device.
* We don't have to invalidate the snapshot in this case, but we need
* to prevent further writes.
*/
int snapshot_overflowed;
/* Origin writes don't trigger exceptions until this is set */
int active;
atomic_t pending_exceptions_count;
/* Protected by "lock" */
sector_t exception_start_sequence;
/* Protected by kcopyd single-threaded callback */
sector_t exception_complete_sequence;
/*
* A list of pending exceptions that completed out of order.
* Protected by kcopyd single-threaded callback.
*/
struct list_head out_of_order_list;
mempool_t *pending_pool;
struct dm_exception_table pending;
struct dm_exception_table complete;
/*
* pe_lock protects all pending_exception operations and access
* as well as the snapshot_bios list.
*/
spinlock_t pe_lock;
/* Chunks with outstanding reads */
spinlock_t tracked_chunk_lock;
struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
/* The on disk metadata handler */
struct dm_exception_store *store;
struct dm_kcopyd_client *kcopyd_client;
/* Wait for events based on state_bits */
unsigned long state_bits;
/* Range of chunks currently being merged. */
chunk_t first_merging_chunk;
int num_merging_chunks;
/*
* The merge operation failed if this flag is set.
* Failure modes are handled as follows:
* - I/O error reading the header
* => don't load the target; abort.
* - Header does not have "valid" flag set
* => use the origin; forget about the snapshot.
* - I/O error when reading exceptions
* => don't load the target; abort.
* (We can't use the intermediate origin state.)
* - I/O error while merging
* => stop merging; set merge_failed; process I/O normally.
*/
int merge_failed;
/*
* Incoming bios that overlap with chunks being merged must wait
* for them to be committed.
*/
struct bio_list bios_queued_during_merge;
};
/*
* state_bits:
* RUNNING_MERGE - Merge operation is in progress.
* SHUTDOWN_MERGE - Set to signal that merge needs to be stopped;
* cleared afterwards.
*/
#define RUNNING_MERGE 0
#define SHUTDOWN_MERGE 1
DECLARE_DM_KCOPYD_THROTTLE_WITH_MODULE_PARM(snapshot_copy_throttle,
"A percentage of time allocated for copy on write");
struct dm_dev *dm_snap_origin(struct dm_snapshot *s)
{
return s->origin;
}
EXPORT_SYMBOL(dm_snap_origin);
struct dm_dev *dm_snap_cow(struct dm_snapshot *s)
{
return s->cow;
}
EXPORT_SYMBOL(dm_snap_cow);
static sector_t chunk_to_sector(struct dm_exception_store *store,
chunk_t chunk)
{
return chunk << store->chunk_shift;
}
static int bdev_equal(struct block_device *lhs, struct block_device *rhs)
{
/*
* There is only ever one instance of a particular block
* device so we can compare pointers safely.
*/
return lhs == rhs;
}
struct dm_snap_pending_exception {
struct dm_exception e;
/*
* Origin buffers waiting for this to complete are held
* in a bio list
*/
struct bio_list origin_bios;
struct bio_list snapshot_bios;
/* Pointer back to snapshot context */
struct dm_snapshot *snap;
/*
* 1 indicates the exception has already been sent to
* kcopyd.
*/
int started;
/* There was copying error. */
int copy_error;
/* A sequence number, it is used for in-order completion. */
sector_t exception_sequence;
struct list_head out_of_order_entry;
/*
* For writing a complete chunk, bypassing the copy.
*/
struct bio *full_bio;
bio_end_io_t *full_bio_end_io;
};
/*
* Hash table mapping origin volumes to lists of snapshots and
* a lock to protect it
*/
static struct kmem_cache *exception_cache;
static struct kmem_cache *pending_cache;
struct dm_snap_tracked_chunk {
struct hlist_node node;
chunk_t chunk;
};
static void init_tracked_chunk(struct bio *bio)
{
struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
INIT_HLIST_NODE(&c->node);
}
static bool is_bio_tracked(struct bio *bio)
{
struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
return !hlist_unhashed(&c->node);
}
static void track_chunk(struct dm_snapshot *s, struct bio *bio, chunk_t chunk)
{
struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
c->chunk = chunk;
spin_lock_irq(&s->tracked_chunk_lock);
hlist_add_head(&c->node,
&s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)]);
spin_unlock_irq(&s->tracked_chunk_lock);
}
static void stop_tracking_chunk(struct dm_snapshot *s, struct bio *bio)
{
struct dm_snap_tracked_chunk *c = dm_per_bio_data(bio, sizeof(struct dm_snap_tracked_chunk));
unsigned long flags;
spin_lock_irqsave(&s->tracked_chunk_lock, flags);
hlist_del(&c->node);
spin_unlock_irqrestore(&s->tracked_chunk_lock, flags);
}
static int __chunk_is_tracked(struct dm_snapshot *s, chunk_t chunk)
{
struct dm_snap_tracked_chunk *c;
int found = 0;
spin_lock_irq(&s->tracked_chunk_lock);
hlist_for_each_entry(c,
&s->tracked_chunk_hash[DM_TRACKED_CHUNK_HASH(chunk)], node) {
if (c->chunk == chunk) {
found = 1;
break;
}
}
spin_unlock_irq(&s->tracked_chunk_lock);
return found;
}
/*
* This conflicting I/O is extremely improbable in the caller,
* so msleep(1) is sufficient and there is no need for a wait queue.
*/
static void __check_for_conflicting_io(struct dm_snapshot *s, chunk_t chunk)
{
while (__chunk_is_tracked(s, chunk))
msleep(1);
}
/*
* One of these per registered origin, held in the snapshot_origins hash
*/
struct origin {
/* The origin device */
struct block_device *bdev;
struct list_head hash_list;
/* List of snapshots for this origin */
struct list_head snapshots;
};
/*
* This structure is allocated for each origin target
*/
struct dm_origin {
struct dm_dev *dev;
struct dm_target *ti;
unsigned split_boundary;
struct list_head hash_list;
};
/*
* Size of the hash table for origin volumes. If we make this
* the size of the minors list then it should be nearly perfect
*/
#define ORIGIN_HASH_SIZE 256
#define ORIGIN_MASK 0xFF
static struct list_head *_origins;
static struct list_head *_dm_origins;
static struct rw_semaphore _origins_lock;
static DECLARE_WAIT_QUEUE_HEAD(_pending_exceptions_done);
static DEFINE_SPINLOCK(_pending_exceptions_done_spinlock);
static uint64_t _pending_exceptions_done_count;
static int init_origin_hash(void)
{
int i;
_origins = kmalloc(ORIGIN_HASH_SIZE * sizeof(struct list_head),
GFP_KERNEL);
if (!_origins) {
DMERR("unable to allocate memory for _origins");
return -ENOMEM;
}
for (i = 0; i < ORIGIN_HASH_SIZE; i++)
INIT_LIST_HEAD(_origins + i);
_dm_origins = kmalloc(ORIGIN_HASH_SIZE * sizeof(struct list_head),
GFP_KERNEL);
if (!_dm_origins) {
DMERR("unable to allocate memory for _dm_origins");
kfree(_origins);
return -ENOMEM;
}
for (i = 0; i < ORIGIN_HASH_SIZE; i++)
INIT_LIST_HEAD(_dm_origins + i);
init_rwsem(&_origins_lock);
return 0;
}
static void exit_origin_hash(void)
{
kfree(_origins);
kfree(_dm_origins);
}
static unsigned origin_hash(struct block_device *bdev)
{
return bdev->bd_dev & ORIGIN_MASK;
}
static struct origin *__lookup_origin(struct block_device *origin)
{
struct list_head *ol;
struct origin *o;
ol = &_origins[origin_hash(origin)];
list_for_each_entry (o, ol, hash_list)
if (bdev_equal(o->bdev, origin))
return o;
return NULL;
}
static void __insert_origin(struct origin *o)
{
struct list_head *sl = &_origins[origin_hash(o->bdev)];
list_add_tail(&o->hash_list, sl);
}
static struct dm_origin *__lookup_dm_origin(struct block_device *origin)
{
struct list_head *ol;
struct dm_origin *o;
ol = &_dm_origins[origin_hash(origin)];
list_for_each_entry (o, ol, hash_list)
if (bdev_equal(o->dev->bdev, origin))
return o;
return NULL;
}
static void __insert_dm_origin(struct dm_origin *o)
{
struct list_head *sl = &_dm_origins[origin_hash(o->dev->bdev)];
list_add_tail(&o->hash_list, sl);
}
static void __remove_dm_origin(struct dm_origin *o)
{
list_del(&o->hash_list);
}
/*
* _origins_lock must be held when calling this function.
* Returns number of snapshots registered using the supplied cow device, plus:
* snap_src - a snapshot suitable for use as a source of exception handover
* snap_dest - a snapshot capable of receiving exception handover.
* snap_merge - an existing snapshot-merge target linked to the same origin.
* There can be at most one snapshot-merge target. The parameter is optional.
*
* Possible return values and states of snap_src and snap_dest.
* 0: NULL, NULL - first new snapshot
* 1: snap_src, NULL - normal snapshot
* 2: snap_src, snap_dest - waiting for handover
* 2: snap_src, NULL - handed over, waiting for old to be deleted
* 1: NULL, snap_dest - source got destroyed without handover
*/
static int __find_snapshots_sharing_cow(struct dm_snapshot *snap,
struct dm_snapshot **snap_src,
struct dm_snapshot **snap_dest,
struct dm_snapshot **snap_merge)
{
struct dm_snapshot *s;
struct origin *o;
int count = 0;
int active;
o = __lookup_origin(snap->origin->bdev);
if (!o)
goto out;
list_for_each_entry(s, &o->snapshots, list) {
if (dm_target_is_snapshot_merge(s->ti) && snap_merge)
*snap_merge = s;
if (!bdev_equal(s->cow->bdev, snap->cow->bdev))
continue;
down_read(&s->lock);
active = s->active;
up_read(&s->lock);
if (active) {
if (snap_src)
*snap_src = s;
} else if (snap_dest)
*snap_dest = s;
count++;
}
out:
return count;
}
/*
* On success, returns 1 if this snapshot is a handover destination,
* otherwise returns 0.
*/
static int __validate_exception_handover(struct dm_snapshot *snap)
{
struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
struct dm_snapshot *snap_merge = NULL;
/* Does snapshot need exceptions handed over to it? */
if ((__find_snapshots_sharing_cow(snap, &snap_src, &snap_dest,
&snap_merge) == 2) ||
snap_dest) {
snap->ti->error = "Snapshot cow pairing for exception "
"table handover failed";
return -EINVAL;
}
/*
* If no snap_src was found, snap cannot become a handover
* destination.
*/
if (!snap_src)
return 0;
/*
* Non-snapshot-merge handover?
*/
if (!dm_target_is_snapshot_merge(snap->ti))
return 1;
/*
* Do not allow more than one merging snapshot.
*/
if (snap_merge) {
snap->ti->error = "A snapshot is already merging.";
return -EINVAL;
}
if (!snap_src->store->type->prepare_merge ||
!snap_src->store->type->commit_merge) {
snap->ti->error = "Snapshot exception store does not "
"support snapshot-merge.";
return -EINVAL;
}
return 1;
}
static void __insert_snapshot(struct origin *o, struct dm_snapshot *s)
{
struct dm_snapshot *l;
/* Sort the list according to chunk size, largest-first smallest-last */
list_for_each_entry(l, &o->snapshots, list)
if (l->store->chunk_size < s->store->chunk_size)
break;
list_add_tail(&s->list, &l->list);
}
/*
* Make a note of the snapshot and its origin so we can look it
* up when the origin has a write on it.
*
* Also validate snapshot exception store handovers.
* On success, returns 1 if this registration is a handover destination,
* otherwise returns 0.
*/
static int register_snapshot(struct dm_snapshot *snap)
{
struct origin *o, *new_o = NULL;
struct block_device *bdev = snap->origin->bdev;
int r = 0;
new_o = kmalloc(sizeof(*new_o), GFP_KERNEL);
if (!new_o)
return -ENOMEM;
down_write(&_origins_lock);
r = __validate_exception_handover(snap);
if (r < 0) {
kfree(new_o);
goto out;
}
o = __lookup_origin(bdev);
if (o)
kfree(new_o);
else {
/* New origin */
o = new_o;
/* Initialise the struct */
INIT_LIST_HEAD(&o->snapshots);
o->bdev = bdev;
__insert_origin(o);
}
__insert_snapshot(o, snap);
out:
up_write(&_origins_lock);
return r;
}
/*
* Move snapshot to correct place in list according to chunk size.
*/
static void reregister_snapshot(struct dm_snapshot *s)
{
struct block_device *bdev = s->origin->bdev;
down_write(&_origins_lock);
list_del(&s->list);
__insert_snapshot(__lookup_origin(bdev), s);
up_write(&_origins_lock);
}
static void unregister_snapshot(struct dm_snapshot *s)
{
struct origin *o;
down_write(&_origins_lock);
o = __lookup_origin(s->origin->bdev);
list_del(&s->list);
if (o && list_empty(&o->snapshots)) {
list_del(&o->hash_list);
kfree(o);
}
up_write(&_origins_lock);
}
/*
* Implementation of the exception hash tables.
* The lowest hash_shift bits of the chunk number are ignored, allowing
* some consecutive chunks to be grouped together.
*/
static int dm_exception_table_init(struct dm_exception_table *et,
uint32_t size, unsigned hash_shift)
{
unsigned int i;
et->hash_shift = hash_shift;
et->hash_mask = size - 1;
et->table = dm_vcalloc(size, sizeof(struct list_head));
if (!et->table)
return -ENOMEM;
for (i = 0; i < size; i++)
INIT_LIST_HEAD(et->table + i);
return 0;
}
static void dm_exception_table_exit(struct dm_exception_table *et,
struct kmem_cache *mem)
{
struct list_head *slot;
struct dm_exception *ex, *next;
int i, size;
size = et->hash_mask + 1;
for (i = 0; i < size; i++) {
slot = et->table + i;
list_for_each_entry_safe (ex, next, slot, hash_list)
kmem_cache_free(mem, ex);
}
vfree(et->table);
}
static uint32_t exception_hash(struct dm_exception_table *et, chunk_t chunk)
{
return (chunk >> et->hash_shift) & et->hash_mask;
}
static void dm_remove_exception(struct dm_exception *e)
{
list_del(&e->hash_list);
}
/*
* Return the exception data for a sector, or NULL if not
* remapped.
*/
static struct dm_exception *dm_lookup_exception(struct dm_exception_table *et,
chunk_t chunk)
{
struct list_head *slot;
struct dm_exception *e;
slot = &et->table[exception_hash(et, chunk)];
list_for_each_entry (e, slot, hash_list)
if (chunk >= e->old_chunk &&
chunk <= e->old_chunk + dm_consecutive_chunk_count(e))
return e;
return NULL;
}
static struct dm_exception *alloc_completed_exception(gfp_t gfp)
{
struct dm_exception *e;
e = kmem_cache_alloc(exception_cache, gfp);
if (!e && gfp == GFP_NOIO)
e = kmem_cache_alloc(exception_cache, GFP_ATOMIC);
return e;
}
static void free_completed_exception(struct dm_exception *e)
{
kmem_cache_free(exception_cache, e);
}
static struct dm_snap_pending_exception *alloc_pending_exception(struct dm_snapshot *s)
{
struct dm_snap_pending_exception *pe = mempool_alloc(s->pending_pool,
GFP_NOIO);
atomic_inc(&s->pending_exceptions_count);
pe->snap = s;
return pe;
}
static void free_pending_exception(struct dm_snap_pending_exception *pe)
{
struct dm_snapshot *s = pe->snap;
mempool_free(pe, s->pending_pool);
smp_mb__before_atomic();
atomic_dec(&s->pending_exceptions_count);
}
static void dm_insert_exception(struct dm_exception_table *eh,
struct dm_exception *new_e)
{
struct list_head *l;
struct dm_exception *e = NULL;
l = &eh->table[exception_hash(eh, new_e->old_chunk)];
/* Add immediately if this table doesn't support consecutive chunks */
if (!eh->hash_shift)
goto out;
/* List is ordered by old_chunk */
list_for_each_entry_reverse(e, l, hash_list) {
/* Insert after an existing chunk? */
if (new_e->old_chunk == (e->old_chunk +
dm_consecutive_chunk_count(e) + 1) &&
new_e->new_chunk == (dm_chunk_number(e->new_chunk) +
dm_consecutive_chunk_count(e) + 1)) {
dm_consecutive_chunk_count_inc(e);
free_completed_exception(new_e);
return;
}
/* Insert before an existing chunk? */
if (new_e->old_chunk == (e->old_chunk - 1) &&
new_e->new_chunk == (dm_chunk_number(e->new_chunk) - 1)) {
dm_consecutive_chunk_count_inc(e);
e->old_chunk--;
e->new_chunk--;
free_completed_exception(new_e);
return;
}
if (new_e->old_chunk > e->old_chunk)
break;
}
out:
list_add(&new_e->hash_list, e ? &e->hash_list : l);
}
/*
* Callback used by the exception stores to load exceptions when
* initialising.
*/
static int dm_add_exception(void *context, chunk_t old, chunk_t new)
{
struct dm_snapshot *s = context;
struct dm_exception *e;
e = alloc_completed_exception(GFP_KERNEL);
if (!e)
return -ENOMEM;
e->old_chunk = old;
/* Consecutive_count is implicitly initialised to zero */
e->new_chunk = new;
dm_insert_exception(&s->complete, e);
return 0;
}
/*
* Return a minimum chunk size of all snapshots that have the specified origin.
* Return zero if the origin has no snapshots.
*/
static uint32_t __minimum_chunk_size(struct origin *o)
{
struct dm_snapshot *snap;
unsigned chunk_size = 0;
if (o)
list_for_each_entry(snap, &o->snapshots, list)
chunk_size = min_not_zero(chunk_size,
snap->store->chunk_size);
return (uint32_t) chunk_size;
}
/*
* Hard coded magic.
*/
static int calc_max_buckets(void)
{
/* use a fixed size of 2MB */
unsigned long mem = 2 * 1024 * 1024;
mem /= sizeof(struct list_head);
return mem;
}
/*
* Allocate room for a suitable hash table.
*/
static int init_hash_tables(struct dm_snapshot *s)
{
sector_t hash_size, cow_dev_size, max_buckets;
/*
* Calculate based on the size of the original volume or
* the COW volume...
*/
cow_dev_size = get_dev_size(s->cow->bdev);
max_buckets = calc_max_buckets();
hash_size = cow_dev_size >> s->store->chunk_shift;
hash_size = min(hash_size, max_buckets);
if (hash_size < 64)
hash_size = 64;
hash_size = rounddown_pow_of_two(hash_size);
if (dm_exception_table_init(&s->complete, hash_size,
DM_CHUNK_CONSECUTIVE_BITS))
return -ENOMEM;
/*
* Allocate hash table for in-flight exceptions
* Make this smaller than the real hash table
*/
hash_size >>= 3;
if (hash_size < 64)
hash_size = 64;
if (dm_exception_table_init(&s->pending, hash_size, 0)) {
dm_exception_table_exit(&s->complete, exception_cache);
return -ENOMEM;
}
return 0;
}
static void merge_shutdown(struct dm_snapshot *s)
{
clear_bit_unlock(RUNNING_MERGE, &s->state_bits);
smp_mb__after_atomic();
wake_up_bit(&s->state_bits, RUNNING_MERGE);
}
static struct bio *__release_queued_bios_after_merge(struct dm_snapshot *s)
{
s->first_merging_chunk = 0;
s->num_merging_chunks = 0;
return bio_list_get(&s->bios_queued_during_merge);
}
/*
* Remove one chunk from the index of completed exceptions.
*/
static int __remove_single_exception_chunk(struct dm_snapshot *s,
chunk_t old_chunk)
{
struct dm_exception *e;
e = dm_lookup_exception(&s->complete, old_chunk);
if (!e) {
DMERR("Corruption detected: exception for block %llu is "
"on disk but not in memory",
(unsigned long long)old_chunk);
return -EINVAL;
}
/*
* If this is the only chunk using this exception, remove exception.
*/
if (!dm_consecutive_chunk_count(e)) {
dm_remove_exception(e);
free_completed_exception(e);
return 0;
}
/*
* The chunk may be either at the beginning or the end of a
* group of consecutive chunks - never in the middle. We are
* removing chunks in the opposite order to that in which they
* were added, so this should always be true.
* Decrement the consecutive chunk counter and adjust the
* starting point if necessary.
*/
if (old_chunk == e->old_chunk) {
e->old_chunk++;
e->new_chunk++;
} else if (old_chunk != e->old_chunk +
dm_consecutive_chunk_count(e)) {
DMERR("Attempt to merge block %llu from the "
"middle of a chunk range [%llu - %llu]",
(unsigned long long)old_chunk,
(unsigned long long)e->old_chunk,
(unsigned long long)
e->old_chunk + dm_consecutive_chunk_count(e));
return -EINVAL;
}
dm_consecutive_chunk_count_dec(e);
return 0;
}
static void flush_bios(struct bio *bio);
static int remove_single_exception_chunk(struct dm_snapshot *s)
{
struct bio *b = NULL;
int r;
chunk_t old_chunk = s->first_merging_chunk + s->num_merging_chunks - 1;
down_write(&s->lock);
/*
* Process chunks (and associated exceptions) in reverse order
* so that dm_consecutive_chunk_count_dec() accounting works.
*/
do {
r = __remove_single_exception_chunk(s, old_chunk);
if (r)
goto out;
} while (old_chunk-- > s->first_merging_chunk);
b = __release_queued_bios_after_merge(s);
out:
up_write(&s->lock);
if (b)
flush_bios(b);
return r;
}
static int origin_write_extent(struct dm_snapshot *merging_snap,
sector_t sector, unsigned chunk_size);
static void merge_callback(int read_err, unsigned long write_err,
void *context);
static uint64_t read_pending_exceptions_done_count(void)
{
uint64_t pending_exceptions_done;
spin_lock(&_pending_exceptions_done_spinlock);
pending_exceptions_done = _pending_exceptions_done_count;
spin_unlock(&_pending_exceptions_done_spinlock);
return pending_exceptions_done;
}
static void increment_pending_exceptions_done_count(void)
{
spin_lock(&_pending_exceptions_done_spinlock);
_pending_exceptions_done_count++;
spin_unlock(&_pending_exceptions_done_spinlock);
wake_up_all(&_pending_exceptions_done);
}
static void snapshot_merge_next_chunks(struct dm_snapshot *s)
{
int i, linear_chunks;
chunk_t old_chunk, new_chunk;
struct dm_io_region src, dest;
sector_t io_size;
uint64_t previous_count;
BUG_ON(!test_bit(RUNNING_MERGE, &s->state_bits));
if (unlikely(test_bit(SHUTDOWN_MERGE, &s->state_bits)))
goto shut;
/*
* valid flag never changes during merge, so no lock required.
*/
if (!s->valid) {
DMERR("Snapshot is invalid: can't merge");
goto shut;
}
linear_chunks = s->store->type->prepare_merge(s->store, &old_chunk,
&new_chunk);
if (linear_chunks <= 0) {
if (linear_chunks < 0) {
DMERR("Read error in exception store: "
"shutting down merge");
down_write(&s->lock);
s->merge_failed = 1;
up_write(&s->lock);
}
goto shut;
}
/* Adjust old_chunk and new_chunk to reflect start of linear region */
old_chunk = old_chunk + 1 - linear_chunks;
new_chunk = new_chunk + 1 - linear_chunks;
/*
* Use one (potentially large) I/O to copy all 'linear_chunks'
* from the exception store to the origin
*/
io_size = linear_chunks * s->store->chunk_size;
dest.bdev = s->origin->bdev;
dest.sector = chunk_to_sector(s->store, old_chunk);
dest.count = min(io_size, get_dev_size(dest.bdev) - dest.sector);
src.bdev = s->cow->bdev;
src.sector = chunk_to_sector(s->store, new_chunk);
src.count = dest.count;
/*
* Reallocate any exceptions needed in other snapshots then
* wait for the pending exceptions to complete.
* Each time any pending exception (globally on the system)
* completes we are woken and repeat the process to find out
* if we can proceed. While this may not seem a particularly
* efficient algorithm, it is not expected to have any
* significant impact on performance.
*/
previous_count = read_pending_exceptions_done_count();
while (origin_write_extent(s, dest.sector, io_size)) {
wait_event(_pending_exceptions_done,
(read_pending_exceptions_done_count() !=
previous_count));
/* Retry after the wait, until all exceptions are done. */
previous_count = read_pending_exceptions_done_count();
}
down_write(&s->lock);
s->first_merging_chunk = old_chunk;
s->num_merging_chunks = linear_chunks;
up_write(&s->lock);
/* Wait until writes to all 'linear_chunks' drain */
for (i = 0; i < linear_chunks; i++)
__check_for_conflicting_io(s, old_chunk + i);
dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, merge_callback, s);
return;
shut:
merge_shutdown(s);
}
static void error_bios(struct bio *bio);
static void merge_callback(int read_err, unsigned long write_err, void *context)
{
struct dm_snapshot *s = context;
struct bio *b = NULL;
if (read_err || write_err) {
if (read_err)
DMERR("Read error: shutting down merge.");
else
DMERR("Write error: shutting down merge.");
goto shut;
}
if (s->store->type->commit_merge(s->store,
s->num_merging_chunks) < 0) {
DMERR("Write error in exception store: shutting down merge");
goto shut;
}
if (remove_single_exception_chunk(s) < 0)
goto shut;
snapshot_merge_next_chunks(s);
return;
shut:
down_write(&s->lock);
s->merge_failed = 1;
b = __release_queued_bios_after_merge(s);
up_write(&s->lock);
error_bios(b);
merge_shutdown(s);
}
static void start_merge(struct dm_snapshot *s)
{
if (!test_and_set_bit(RUNNING_MERGE, &s->state_bits))
snapshot_merge_next_chunks(s);
}
/*
* Stop the merging process and wait until it finishes.
*/
static void stop_merge(struct dm_snapshot *s)
{
set_bit(SHUTDOWN_MERGE, &s->state_bits);
wait_on_bit(&s->state_bits, RUNNING_MERGE, TASK_UNINTERRUPTIBLE);
clear_bit(SHUTDOWN_MERGE, &s->state_bits);
}
/*
* Construct a snapshot mapping: <origin_dev> <COW-dev> <p|po|n> <chunk-size>
*/
static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
{
struct dm_snapshot *s;
int i;
int r = -EINVAL;
char *origin_path, *cow_path;
dev_t origin_dev, cow_dev;
unsigned args_used, num_flush_bios = 1;
fmode_t origin_mode = FMODE_READ;
if (argc != 4) {
ti->error = "requires exactly 4 arguments";
r = -EINVAL;
goto bad;
}
if (dm_target_is_snapshot_merge(ti)) {
num_flush_bios = 2;
origin_mode = FMODE_WRITE;
}
s = kmalloc(sizeof(*s), GFP_KERNEL);
if (!s) {
ti->error = "Cannot allocate private snapshot structure";
r = -ENOMEM;
goto bad;
}
origin_path = argv[0];
argv++;
argc--;
r = dm_get_device(ti, origin_path, origin_mode, &s->origin);
if (r) {
ti->error = "Cannot get origin device";
goto bad_origin;
}
origin_dev = s->origin->bdev->bd_dev;
cow_path = argv[0];
argv++;
argc--;
cow_dev = dm_get_dev_t(cow_path);
if (cow_dev && cow_dev == origin_dev) {
ti->error = "COW device cannot be the same as origin device";
r = -EINVAL;
goto bad_cow;
}
r = dm_get_device(ti, cow_path, dm_table_get_mode(ti->table), &s->cow);
if (r) {
ti->error = "Cannot get COW device";
goto bad_cow;
}
r = dm_exception_store_create(ti, argc, argv, s, &args_used, &s->store);
if (r) {
ti->error = "Couldn't create exception store";
r = -EINVAL;
goto bad_store;
}
argv += args_used;
argc -= args_used;
s->ti = ti;
s->valid = 1;
s->snapshot_overflowed = 0;
s->active = 0;
atomic_set(&s->pending_exceptions_count, 0);
s->exception_start_sequence = 0;
s->exception_complete_sequence = 0;
INIT_LIST_HEAD(&s->out_of_order_list);
init_rwsem(&s->lock);
INIT_LIST_HEAD(&s->list);
spin_lock_init(&s->pe_lock);
s->state_bits = 0;
s->merge_failed = 0;
s->first_merging_chunk = 0;
s->num_merging_chunks = 0;
bio_list_init(&s->bios_queued_during_merge);
/* Allocate hash table for COW data */
if (init_hash_tables(s)) {
ti->error = "Unable to allocate hash table space";
r = -ENOMEM;
goto bad_hash_tables;
}
s->kcopyd_client = dm_kcopyd_client_create(&dm_kcopyd_throttle);
if (IS_ERR(s->kcopyd_client)) {
r = PTR_ERR(s->kcopyd_client);
ti->error = "Could not create kcopyd client";
goto bad_kcopyd;
}
s->pending_pool = mempool_create_slab_pool(MIN_IOS, pending_cache);
if (!s->pending_pool) {
ti->error = "Could not allocate mempool for pending exceptions";
r = -ENOMEM;
goto bad_pending_pool;
}
for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
INIT_HLIST_HEAD(&s->tracked_chunk_hash[i]);
spin_lock_init(&s->tracked_chunk_lock);
ti->private = s;
ti->num_flush_bios = num_flush_bios;
ti->per_io_data_size = sizeof(struct dm_snap_tracked_chunk);
/* Add snapshot to the list of snapshots for this origin */
/* Exceptions aren't triggered till snapshot_resume() is called */
r = register_snapshot(s);
if (r == -ENOMEM) {
ti->error = "Snapshot origin struct allocation failed";
goto bad_load_and_register;
} else if (r < 0) {
/* invalid handover, register_snapshot has set ti->error */
goto bad_load_and_register;
}
/*
* Metadata must only be loaded into one table at once, so skip this
* if metadata will be handed over during resume.
* Chunk size will be set during the handover - set it to zero to
* ensure it's ignored.
*/
if (r > 0) {
s->store->chunk_size = 0;
return 0;
}
r = s->store->type->read_metadata(s->store, dm_add_exception,
(void *)s);
if (r < 0) {
ti->error = "Failed to read snapshot metadata";
goto bad_read_metadata;
} else if (r > 0) {
s->valid = 0;
DMWARN("Snapshot is marked invalid.");
}
if (!s->store->chunk_size) {
ti->error = "Chunk size not set";
goto bad_read_metadata;
}
r = dm_set_target_max_io_len(ti, s->store->chunk_size);
if (r)
goto bad_read_metadata;
return 0;
bad_read_metadata:
unregister_snapshot(s);
bad_load_and_register:
mempool_destroy(s->pending_pool);
bad_pending_pool:
dm_kcopyd_client_destroy(s->kcopyd_client);
bad_kcopyd:
dm_exception_table_exit(&s->pending, pending_cache);
dm_exception_table_exit(&s->complete, exception_cache);
bad_hash_tables:
dm_exception_store_destroy(s->store);
bad_store:
dm_put_device(ti, s->cow);
bad_cow:
dm_put_device(ti, s->origin);
bad_origin:
kfree(s);
bad:
return r;
}
static void __free_exceptions(struct dm_snapshot *s)
{
dm_kcopyd_client_destroy(s->kcopyd_client);
s->kcopyd_client = NULL;
dm_exception_table_exit(&s->pending, pending_cache);
dm_exception_table_exit(&s->complete, exception_cache);
}
static void __handover_exceptions(struct dm_snapshot *snap_src,
struct dm_snapshot *snap_dest)
{
union {
struct dm_exception_table table_swap;
struct dm_exception_store *store_swap;
} u;
/*
* Swap all snapshot context information between the two instances.
*/
u.table_swap = snap_dest->complete;
snap_dest->complete = snap_src->complete;
snap_src->complete = u.table_swap;
u.store_swap = snap_dest->store;
snap_dest->store = snap_src->store;
snap_dest->store->userspace_supports_overflow = u.store_swap->userspace_supports_overflow;
snap_src->store = u.store_swap;
snap_dest->store->snap = snap_dest;
snap_src->store->snap = snap_src;
snap_dest->ti->max_io_len = snap_dest->store->chunk_size;
snap_dest->valid = snap_src->valid;
snap_dest->snapshot_overflowed = snap_src->snapshot_overflowed;
/*
* Set source invalid to ensure it receives no further I/O.
*/
snap_src->valid = 0;
}
static void snapshot_dtr(struct dm_target *ti)
{
#ifdef CONFIG_DM_DEBUG
int i;
#endif
struct dm_snapshot *s = ti->private;
struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
down_read(&_origins_lock);
/* Check whether exception handover must be cancelled */
(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
if (snap_src && snap_dest && (s == snap_src)) {
down_write(&snap_dest->lock);
snap_dest->valid = 0;
up_write(&snap_dest->lock);
DMERR("Cancelling snapshot handover.");
}
up_read(&_origins_lock);
if (dm_target_is_snapshot_merge(ti))
stop_merge(s);
/* Prevent further origin writes from using this snapshot. */
/* After this returns there can be no new kcopyd jobs. */
unregister_snapshot(s);
while (atomic_read(&s->pending_exceptions_count))
msleep(1);
/*
* Ensure instructions in mempool_destroy aren't reordered
* before atomic_read.
*/
smp_mb();
#ifdef CONFIG_DM_DEBUG
for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
BUG_ON(!hlist_empty(&s->tracked_chunk_hash[i]));
#endif
__free_exceptions(s);
mempool_destroy(s->pending_pool);
dm_exception_store_destroy(s->store);
dm_put_device(ti, s->cow);
dm_put_device(ti, s->origin);
kfree(s);
}
/*
* Flush a list of buffers.
*/
static void flush_bios(struct bio *bio)
{
struct bio *n;
while (bio) {
n = bio->bi_next;
bio->bi_next = NULL;
generic_make_request(bio);
bio = n;
}
}
static int do_origin(struct dm_dev *origin, struct bio *bio);
/*
* Flush a list of buffers.
*/
static void retry_origin_bios(struct dm_snapshot *s, struct bio *bio)
{
struct bio *n;
int r;
while (bio) {
n = bio->bi_next;
bio->bi_next = NULL;
r = do_origin(s->origin, bio);
if (r == DM_MAPIO_REMAPPED)
generic_make_request(bio);
bio = n;
}
}
/*
* Error a list of buffers.
*/
static void error_bios(struct bio *bio)
{
struct bio *n;
while (bio) {
n = bio->bi_next;
bio->bi_next = NULL;
bio_io_error(bio);
bio = n;
}
}
static void __invalidate_snapshot(struct dm_snapshot *s, int err)
{
if (!s->valid)
return;
if (err == -EIO)
DMERR("Invalidating snapshot: Error reading/writing.");
else if (err == -ENOMEM)
DMERR("Invalidating snapshot: Unable to allocate exception.");
if (s->store->type->drop_snapshot)
s->store->type->drop_snapshot(s->store);
s->valid = 0;
dm_table_event(s->ti->table);
}
static void pending_complete(void *context, int success)
{
struct dm_snap_pending_exception *pe = context;
struct dm_exception *e;
struct dm_snapshot *s = pe->snap;
struct bio *origin_bios = NULL;
struct bio *snapshot_bios = NULL;
struct bio *full_bio = NULL;
int error = 0;
if (!success) {
/* Read/write error - snapshot is unusable */
down_write(&s->lock);
__invalidate_snapshot(s, -EIO);
error = 1;
goto out;
}
e = alloc_completed_exception(GFP_NOIO);
if (!e) {
down_write(&s->lock);
__invalidate_snapshot(s, -ENOMEM);
error = 1;
goto out;
}
*e = pe->e;
down_write(&s->lock);
if (!s->valid) {
free_completed_exception(e);
error = 1;
goto out;
}
/* Check for conflicting reads */
__check_for_conflicting_io(s, pe->e.old_chunk);
/*
* Add a proper exception, and remove the
* in-flight exception from the list.
*/
dm_insert_exception(&s->complete, e);
out:
dm_remove_exception(&pe->e);
snapshot_bios = bio_list_get(&pe->snapshot_bios);
origin_bios = bio_list_get(&pe->origin_bios);
full_bio = pe->full_bio;
if (full_bio)
full_bio->bi_end_io = pe->full_bio_end_io;
increment_pending_exceptions_done_count();
up_write(&s->lock);
/* Submit any pending write bios */
if (error) {
if (full_bio)
bio_io_error(full_bio);
error_bios(snapshot_bios);
} else {
if (full_bio)
bio_endio(full_bio);
flush_bios(snapshot_bios);
}
retry_origin_bios(s, origin_bios);
free_pending_exception(pe);
}
static void complete_exception(struct dm_snap_pending_exception *pe)
{
struct dm_snapshot *s = pe->snap;
/* Update the metadata if we are persistent */
s->store->type->commit_exception(s->store, &pe->e, !pe->copy_error,
pending_complete, pe);
}
/*
* Called when the copy I/O has finished. kcopyd actually runs
* this code so don't block.
*/
static void copy_callback(int read_err, unsigned long write_err, void *context)
{
struct dm_snap_pending_exception *pe = context;
struct dm_snapshot *s = pe->snap;
pe->copy_error = read_err || write_err;
if (pe->exception_sequence == s->exception_complete_sequence) {
s->exception_complete_sequence++;
complete_exception(pe);
while (!list_empty(&s->out_of_order_list)) {
pe = list_entry(s->out_of_order_list.next,
struct dm_snap_pending_exception, out_of_order_entry);
if (pe->exception_sequence != s->exception_complete_sequence)
break;
s->exception_complete_sequence++;
list_del(&pe->out_of_order_entry);
complete_exception(pe);
}
} else {
struct list_head *lh;
struct dm_snap_pending_exception *pe2;
list_for_each_prev(lh, &s->out_of_order_list) {
pe2 = list_entry(lh, struct dm_snap_pending_exception, out_of_order_entry);
if (pe2->exception_sequence < pe->exception_sequence)
break;
}
list_add(&pe->out_of_order_entry, lh);
}
}
/*
* Dispatches the copy operation to kcopyd.
*/
static void start_copy(struct dm_snap_pending_exception *pe)
{
struct dm_snapshot *s = pe->snap;
struct dm_io_region src, dest;
struct block_device *bdev = s->origin->bdev;
sector_t dev_size;
dev_size = get_dev_size(bdev);
src.bdev = bdev;
src.sector = chunk_to_sector(s->store, pe->e.old_chunk);
src.count = min((sector_t)s->store->chunk_size, dev_size - src.sector);
dest.bdev = s->cow->bdev;
dest.sector = chunk_to_sector(s->store, pe->e.new_chunk);
dest.count = src.count;
/* Hand over to kcopyd */
dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, copy_callback, pe);
}
static void full_bio_end_io(struct bio *bio)
{
void *callback_data = bio->bi_private;
dm_kcopyd_do_callback(callback_data, 0, bio->bi_status ? 1 : 0);
}
static void start_full_bio(struct dm_snap_pending_exception *pe,
struct bio *bio)
{
struct dm_snapshot *s = pe->snap;
void *callback_data;
pe->full_bio = bio;
pe->full_bio_end_io = bio->bi_end_io;
callback_data = dm_kcopyd_prepare_callback(s->kcopyd_client,
copy_callback, pe);
bio->bi_end_io = full_bio_end_io;
bio->bi_private = callback_data;
generic_make_request(bio);
}
static struct dm_snap_pending_exception *
__lookup_pending_exception(struct dm_snapshot *s, chunk_t chunk)
{
struct dm_exception *e = dm_lookup_exception(&s->pending, chunk);
if (!e)
return NULL;
return container_of(e, struct dm_snap_pending_exception, e);
}
/*
* Looks to see if this snapshot already has a pending exception
* for this chunk, otherwise it allocates a new one and inserts
* it into the pending table.
*
* NOTE: a write lock must be held on snap->lock before calling
* this.
*/
static struct dm_snap_pending_exception *
__find_pending_exception(struct dm_snapshot *s,
struct dm_snap_pending_exception *pe, chunk_t chunk)
{
struct dm_snap_pending_exception *pe2;
pe2 = __lookup_pending_exception(s, chunk);
if (pe2) {
free_pending_exception(pe);
return pe2;
}
pe->e.old_chunk = chunk;
bio_list_init(&pe->origin_bios);
bio_list_init(&pe->snapshot_bios);
pe->started = 0;
pe->full_bio = NULL;
if (s->store->type->prepare_exception(s->store, &pe->e)) {
free_pending_exception(pe);
return NULL;
}
pe->exception_sequence = s->exception_start_sequence++;
dm_insert_exception(&s->pending, &pe->e);
return pe;
}
static void remap_exception(struct dm_snapshot *s, struct dm_exception *e,
struct bio *bio, chunk_t chunk)
{
bio_set_dev(bio, s->cow->bdev);
bio->bi_iter.bi_sector =
chunk_to_sector(s->store, dm_chunk_number(e->new_chunk) +
(chunk - e->old_chunk)) +
(bio->bi_iter.bi_sector & s->store->chunk_mask);
}
static int snapshot_map(struct dm_target *ti, struct bio *bio)
{
struct dm_exception *e;
struct dm_snapshot *s = ti->private;
int r = DM_MAPIO_REMAPPED;
chunk_t chunk;
struct dm_snap_pending_exception *pe = NULL;
init_tracked_chunk(bio);
if (bio->bi_opf & REQ_PREFLUSH) {
bio_set_dev(bio, s->cow->bdev);
return DM_MAPIO_REMAPPED;
}
chunk = sector_to_chunk(s->store, bio->bi_iter.bi_sector);
/* Full snapshots are not usable */
/* To get here the table must be live so s->active is always set. */
if (!s->valid)
return DM_MAPIO_KILL;
/* FIXME: should only take write lock if we need
* to copy an exception */
down_write(&s->lock);
if (!s->valid || (unlikely(s->snapshot_overflowed) &&
bio_data_dir(bio) == WRITE)) {
r = DM_MAPIO_KILL;
goto out_unlock;
}
/* If the block is already remapped - use that, else remap it */
e = dm_lookup_exception(&s->complete, chunk);
if (e) {
remap_exception(s, e, bio, chunk);
goto out_unlock;
}
/*
* Write to snapshot - higher level takes care of RW/RO
* flags so we should only get this if we are
* writeable.
*/
if (bio_data_dir(bio) == WRITE) {
pe = __lookup_pending_exception(s, chunk);
if (!pe) {
up_write(&s->lock);
pe = alloc_pending_exception(s);
down_write(&s->lock);
if (!s->valid || s->snapshot_overflowed) {
free_pending_exception(pe);
r = DM_MAPIO_KILL;
goto out_unlock;
}
e = dm_lookup_exception(&s->complete, chunk);
if (e) {
free_pending_exception(pe);
remap_exception(s, e, bio, chunk);
goto out_unlock;
}
pe = __find_pending_exception(s, pe, chunk);
if (!pe) {
if (s->store->userspace_supports_overflow) {
s->snapshot_overflowed = 1;
DMERR("Snapshot overflowed: Unable to allocate exception.");
} else
__invalidate_snapshot(s, -ENOMEM);
r = DM_MAPIO_KILL;
goto out_unlock;
}
}
remap_exception(s, &pe->e, bio, chunk);
r = DM_MAPIO_SUBMITTED;
if (!pe->started &&
bio->bi_iter.bi_size ==
(s->store->chunk_size << SECTOR_SHIFT)) {
pe->started = 1;
up_write(&s->lock);
start_full_bio(pe, bio);
goto out;
}
bio_list_add(&pe->snapshot_bios, bio);
if (!pe->started) {
/* this is protected by snap->lock */
pe->started = 1;
up_write(&s->lock);
start_copy(pe);
goto out;
}
} else {
bio_set_dev(bio, s->origin->bdev);
track_chunk(s, bio, chunk);
}
out_unlock:
up_write(&s->lock);
out:
return r;
}
/*
* A snapshot-merge target behaves like a combination of a snapshot
* target and a snapshot-origin target. It only generates new
* exceptions in other snapshots and not in the one that is being
* merged.
*
* For each chunk, if there is an existing exception, it is used to
* redirect I/O to the cow device. Otherwise I/O is sent to the origin,
* which in turn might generate exceptions in other snapshots.
* If merging is currently taking place on the chunk in question, the
* I/O is deferred by adding it to s->bios_queued_during_merge.
*/
static int snapshot_merge_map(struct dm_target *ti, struct bio *bio)
{
struct dm_exception *e;
struct dm_snapshot *s = ti->private;
int r = DM_MAPIO_REMAPPED;
chunk_t chunk;
init_tracked_chunk(bio);
if (bio->bi_opf & REQ_PREFLUSH) {
if (!dm_bio_get_target_bio_nr(bio))
bio_set_dev(bio, s->origin->bdev);
else
bio_set_dev(bio, s->cow->bdev);
return DM_MAPIO_REMAPPED;
}
chunk = sector_to_chunk(s->store, bio->bi_iter.bi_sector);
down_write(&s->lock);
/* Full merging snapshots are redirected to the origin */
if (!s->valid)
goto redirect_to_origin;
/* If the block is already remapped - use that */
e = dm_lookup_exception(&s->complete, chunk);
if (e) {
/* Queue writes overlapping with chunks being merged */
if (bio_data_dir(bio) == WRITE &&
chunk >= s->first_merging_chunk &&
chunk < (s->first_merging_chunk +
s->num_merging_chunks)) {
bio_set_dev(bio, s->origin->bdev);
bio_list_add(&s->bios_queued_during_merge, bio);
r = DM_MAPIO_SUBMITTED;
goto out_unlock;
}
remap_exception(s, e, bio, chunk);
if (bio_data_dir(bio) == WRITE)
track_chunk(s, bio, chunk);
goto out_unlock;
}
redirect_to_origin:
bio_set_dev(bio, s->origin->bdev);
if (bio_data_dir(bio) == WRITE) {
up_write(&s->lock);
return do_origin(s->origin, bio);
}
out_unlock:
up_write(&s->lock);
return r;
}
static int snapshot_end_io(struct dm_target *ti, struct bio *bio,
blk_status_t *error)
{
struct dm_snapshot *s = ti->private;
if (is_bio_tracked(bio))
stop_tracking_chunk(s, bio);
return DM_ENDIO_DONE;
}
static void snapshot_merge_presuspend(struct dm_target *ti)
{
struct dm_snapshot *s = ti->private;
stop_merge(s);
}
static int snapshot_preresume(struct dm_target *ti)
{
int r = 0;
struct dm_snapshot *s = ti->private;
struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
down_read(&_origins_lock);
(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
if (snap_src && snap_dest) {
down_read(&snap_src->lock);
if (s == snap_src) {
DMERR("Unable to resume snapshot source until "
"handover completes.");
r = -EINVAL;
} else if (!dm_suspended(snap_src->ti)) {
DMERR("Unable to perform snapshot handover until "
"source is suspended.");
r = -EINVAL;
}
up_read(&snap_src->lock);
}
up_read(&_origins_lock);
return r;
}
static void snapshot_resume(struct dm_target *ti)
{
struct dm_snapshot *s = ti->private;
struct dm_snapshot *snap_src = NULL, *snap_dest = NULL, *snap_merging = NULL;
struct dm_origin *o;
struct mapped_device *origin_md = NULL;
bool must_restart_merging = false;
down_read(&_origins_lock);
o = __lookup_dm_origin(s->origin->bdev);
if (o)
origin_md = dm_table_get_md(o->ti->table);
if (!origin_md) {
(void) __find_snapshots_sharing_cow(s, NULL, NULL, &snap_merging);
if (snap_merging)
origin_md = dm_table_get_md(snap_merging->ti->table);
}
if (origin_md == dm_table_get_md(ti->table))
origin_md = NULL;
if (origin_md) {
if (dm_hold(origin_md))
origin_md = NULL;
}
up_read(&_origins_lock);
if (origin_md) {
dm_internal_suspend_fast(origin_md);
if (snap_merging && test_bit(RUNNING_MERGE, &snap_merging->state_bits)) {
must_restart_merging = true;
stop_merge(snap_merging);
}
}
down_read(&_origins_lock);
(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
if (snap_src && snap_dest) {
down_write(&snap_src->lock);
down_write_nested(&snap_dest->lock, SINGLE_DEPTH_NESTING);
__handover_exceptions(snap_src, snap_dest);
up_write(&snap_dest->lock);
up_write(&snap_src->lock);
}
up_read(&_origins_lock);
if (origin_md) {
if (must_restart_merging)
start_merge(snap_merging);
dm_internal_resume_fast(origin_md);
dm_put(origin_md);
}
/* Now we have correct chunk size, reregister */
reregister_snapshot(s);
down_write(&s->lock);
s->active = 1;
up_write(&s->lock);
}
static uint32_t get_origin_minimum_chunksize(struct block_device *bdev)
{
uint32_t min_chunksize;
down_read(&_origins_lock);
min_chunksize = __minimum_chunk_size(__lookup_origin(bdev));
up_read(&_origins_lock);
return min_chunksize;
}
static void snapshot_merge_resume(struct dm_target *ti)
{
struct dm_snapshot *s = ti->private;
/*
* Handover exceptions from existing snapshot.
*/
snapshot_resume(ti);
/*
* snapshot-merge acts as an origin, so set ti->max_io_len
*/
ti->max_io_len = get_origin_minimum_chunksize(s->origin->bdev);
start_merge(s);
}
static void snapshot_status(struct dm_target *ti, status_type_t type,
unsigned status_flags, char *result, unsigned maxlen)
{
unsigned sz = 0;
struct dm_snapshot *snap = ti->private;
switch (type) {
case STATUSTYPE_INFO:
down_write(&snap->lock);
if (!snap->valid)
DMEMIT("Invalid");
else if (snap->merge_failed)
DMEMIT("Merge failed");
else if (snap->snapshot_overflowed)
DMEMIT("Overflow");
else {
if (snap->store->type->usage) {
sector_t total_sectors, sectors_allocated,
metadata_sectors;
snap->store->type->usage(snap->store,
&total_sectors,
&sectors_allocated,
&metadata_sectors);
DMEMIT("%llu/%llu %llu",
(unsigned long long)sectors_allocated,
(unsigned long long)total_sectors,
(unsigned long long)metadata_sectors);
}
else
DMEMIT("Unknown");
}
up_write(&snap->lock);
break;
case STATUSTYPE_TABLE:
/*
* kdevname returns a static pointer so we need
* to make private copies if the output is to
* make sense.
*/
DMEMIT("%s %s", snap->origin->name, snap->cow->name);
snap->store->type->status(snap->store, type, result + sz,
maxlen - sz);
break;
}
}
static int snapshot_iterate_devices(struct dm_target *ti,
iterate_devices_callout_fn fn, void *data)
{
struct dm_snapshot *snap = ti->private;
int r;
r = fn(ti, snap->origin, 0, ti->len, data);
if (!r)
r = fn(ti, snap->cow, 0, get_dev_size(snap->cow->bdev), data);
return r;
}
/*-----------------------------------------------------------------
* Origin methods
*---------------------------------------------------------------*/
/*
* If no exceptions need creating, DM_MAPIO_REMAPPED is returned and any
* supplied bio was ignored. The caller may submit it immediately.
* (No remapping actually occurs as the origin is always a direct linear
* map.)
*
* If further exceptions are required, DM_MAPIO_SUBMITTED is returned
* and any supplied bio is added to a list to be submitted once all
* the necessary exceptions exist.
*/
static int __origin_write(struct list_head *snapshots, sector_t sector,
struct bio *bio)
{
int r = DM_MAPIO_REMAPPED;
struct dm_snapshot *snap;
struct dm_exception *e;
struct dm_snap_pending_exception *pe;
struct dm_snap_pending_exception *pe_to_start_now = NULL;
struct dm_snap_pending_exception *pe_to_start_last = NULL;
chunk_t chunk;
/* Do all the snapshots on this origin */
list_for_each_entry (snap, snapshots, list) {
/*
* Don't make new exceptions in a merging snapshot
* because it has effectively been deleted
*/
if (dm_target_is_snapshot_merge(snap->ti))
continue;
down_write(&snap->lock);
/* Only deal with valid and active snapshots */
if (!snap->valid || !snap->active)
goto next_snapshot;
/* Nothing to do if writing beyond end of snapshot */
if (sector >= dm_table_get_size(snap->ti->table))
goto next_snapshot;
/*
* Remember, different snapshots can have
* different chunk sizes.
*/
chunk = sector_to_chunk(snap->store, sector);
/*
* Check exception table to see if block
* is already remapped in this snapshot
* and trigger an exception if not.
*/
e = dm_lookup_exception(&snap->complete, chunk);
if (e)
goto next_snapshot;
pe = __lookup_pending_exception(snap, chunk);
if (!pe) {
up_write(&snap->lock);
pe = alloc_pending_exception(snap);
down_write(&snap->lock);
if (!snap->valid) {
free_pending_exception(pe);
goto next_snapshot;
}
e = dm_lookup_exception(&snap->complete, chunk);
if (e) {
free_pending_exception(pe);
goto next_snapshot;
}
pe = __find_pending_exception(snap, pe, chunk);
if (!pe) {
__invalidate_snapshot(snap, -ENOMEM);
goto next_snapshot;
}
}
r = DM_MAPIO_SUBMITTED;
/*
* If an origin bio was supplied, queue it to wait for the
* completion of this exception, and start this one last,
* at the end of the function.
*/
if (bio) {
bio_list_add(&pe->origin_bios, bio);
bio = NULL;
if (!pe->started) {
pe->started = 1;
pe_to_start_last = pe;
}
}
if (!pe->started) {
pe->started = 1;
pe_to_start_now = pe;
}
next_snapshot:
up_write(&snap->lock);
if (pe_to_start_now) {
start_copy(pe_to_start_now);
pe_to_start_now = NULL;
}
}
/*
* Submit the exception against which the bio is queued last,
* to give the other exceptions a head start.
*/
if (pe_to_start_last)
start_copy(pe_to_start_last);
return r;
}
/*
* Called on a write from the origin driver.
*/
static int do_origin(struct dm_dev *origin, struct bio *bio)
{
struct origin *o;
int r = DM_MAPIO_REMAPPED;
down_read(&_origins_lock);
o = __lookup_origin(origin->bdev);
if (o)
r = __origin_write(&o->snapshots, bio->bi_iter.bi_sector, bio);
up_read(&_origins_lock);
return r;
}
/*
* Trigger exceptions in all non-merging snapshots.
*
* The chunk size of the merging snapshot may be larger than the chunk
* size of some other snapshot so we may need to reallocate multiple
* chunks in other snapshots.
*
* We scan all the overlapping exceptions in the other snapshots.
* Returns 1 if anything was reallocated and must be waited for,
* otherwise returns 0.
*
* size must be a multiple of merging_snap's chunk_size.
*/
static int origin_write_extent(struct dm_snapshot *merging_snap,
sector_t sector, unsigned size)
{
int must_wait = 0;
sector_t n;
struct origin *o;
/*
* The origin's __minimum_chunk_size() got stored in max_io_len
* by snapshot_merge_resume().
*/
down_read(&_origins_lock);
o = __lookup_origin(merging_snap->origin->bdev);
for (n = 0; n < size; n += merging_snap->ti->max_io_len)
if (__origin_write(&o->snapshots, sector + n, NULL) ==
DM_MAPIO_SUBMITTED)
must_wait = 1;
up_read(&_origins_lock);
return must_wait;
}
/*
* Origin: maps a linear range of a device, with hooks for snapshotting.
*/
/*
* Construct an origin mapping: <dev_path>
* The context for an origin is merely a 'struct dm_dev *'
* pointing to the real device.
*/
static int origin_ctr(struct dm_target *ti, unsigned int argc, char **argv)
{
int r;
struct dm_origin *o;
if (argc != 1) {
ti->error = "origin: incorrect number of arguments";
return -EINVAL;
}
o = kmalloc(sizeof(struct dm_origin), GFP_KERNEL);
if (!o) {
ti->error = "Cannot allocate private origin structure";
r = -ENOMEM;
goto bad_alloc;
}
r = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &o->dev);
if (r) {
ti->error = "Cannot get target device";
goto bad_open;
}
o->ti = ti;
ti->private = o;
ti->num_flush_bios = 1;
return 0;
bad_open:
kfree(o);
bad_alloc:
return r;
}
static void origin_dtr(struct dm_target *ti)
{
struct dm_origin *o = ti->private;
dm_put_device(ti, o->dev);
kfree(o);
}
static int origin_map(struct dm_target *ti, struct bio *bio)
{
struct dm_origin *o = ti->private;
unsigned available_sectors;
bio_set_dev(bio, o->dev->bdev);
if (unlikely(bio->bi_opf & REQ_PREFLUSH))
return DM_MAPIO_REMAPPED;
if (bio_data_dir(bio) != WRITE)
return DM_MAPIO_REMAPPED;
available_sectors = o->split_boundary -
((unsigned)bio->bi_iter.bi_sector & (o->split_boundary - 1));
if (bio_sectors(bio) > available_sectors)
dm_accept_partial_bio(bio, available_sectors);
/* Only tell snapshots if this is a write */
return do_origin(o->dev, bio);
}
static long origin_dax_direct_access(struct dm_target *ti, pgoff_t pgoff,
long nr_pages, void **kaddr, pfn_t *pfn)
{
DMWARN("device does not support dax.");
return -EIO;
}
/*
* Set the target "max_io_len" field to the minimum of all the snapshots'
* chunk sizes.
*/
static void origin_resume(struct dm_target *ti)
{
struct dm_origin *o = ti->private;
o->split_boundary = get_origin_minimum_chunksize(o->dev->bdev);
down_write(&_origins_lock);
__insert_dm_origin(o);
up_write(&_origins_lock);
}
static void origin_postsuspend(struct dm_target *ti)
{
struct dm_origin *o = ti->private;
down_write(&_origins_lock);
__remove_dm_origin(o);
up_write(&_origins_lock);
}
static void origin_status(struct dm_target *ti, status_type_t type,
unsigned status_flags, char *result, unsigned maxlen)
{
struct dm_origin *o = ti->private;
switch (type) {
case STATUSTYPE_INFO:
result[0] = '\0';
break;
case STATUSTYPE_TABLE:
snprintf(result, maxlen, "%s", o->dev->name);
break;
}
}
static int origin_iterate_devices(struct dm_target *ti,
iterate_devices_callout_fn fn, void *data)
{
struct dm_origin *o = ti->private;
return fn(ti, o->dev, 0, ti->len, data);
}
static struct target_type origin_target = {
.name = "snapshot-origin",
.version = {1, 9, 0},
.module = THIS_MODULE,
.ctr = origin_ctr,
.dtr = origin_dtr,
.map = origin_map,
.resume = origin_resume,
.postsuspend = origin_postsuspend,
.status = origin_status,
.iterate_devices = origin_iterate_devices,
.direct_access = origin_dax_direct_access,
};
static struct target_type snapshot_target = {
.name = "snapshot",
.version = {1, 15, 0},
.module = THIS_MODULE,
.ctr = snapshot_ctr,
.dtr = snapshot_dtr,
.map = snapshot_map,
.end_io = snapshot_end_io,
.preresume = snapshot_preresume,
.resume = snapshot_resume,
.status = snapshot_status,
.iterate_devices = snapshot_iterate_devices,
};
static struct target_type merge_target = {
.name = dm_snapshot_merge_target_name,
.version = {1, 4, 0},
.module = THIS_MODULE,
.ctr = snapshot_ctr,
.dtr = snapshot_dtr,
.map = snapshot_merge_map,
.end_io = snapshot_end_io,
.presuspend = snapshot_merge_presuspend,
.preresume = snapshot_preresume,
.resume = snapshot_merge_resume,
.status = snapshot_status,
.iterate_devices = snapshot_iterate_devices,
};
static int __init dm_snapshot_init(void)
{
int r;
r = dm_exception_store_init();
if (r) {
DMERR("Failed to initialize exception stores");
return r;
}
r = dm_register_target(&snapshot_target);
if (r < 0) {
DMERR("snapshot target register failed %d", r);
goto bad_register_snapshot_target;
}
r = dm_register_target(&origin_target);
if (r < 0) {
DMERR("Origin target register failed %d", r);
goto bad_register_origin_target;
}
r = dm_register_target(&merge_target);
if (r < 0) {
DMERR("Merge target register failed %d", r);
goto bad_register_merge_target;
}
r = init_origin_hash();
if (r) {
DMERR("init_origin_hash failed.");
goto bad_origin_hash;
}
exception_cache = KMEM_CACHE(dm_exception, 0);
if (!exception_cache) {
DMERR("Couldn't create exception cache.");
r = -ENOMEM;
goto bad_exception_cache;
}
pending_cache = KMEM_CACHE(dm_snap_pending_exception, 0);
if (!pending_cache) {
DMERR("Couldn't create pending cache.");
r = -ENOMEM;
goto bad_pending_cache;
}
return 0;
bad_pending_cache:
kmem_cache_destroy(exception_cache);
bad_exception_cache:
exit_origin_hash();
bad_origin_hash:
dm_unregister_target(&merge_target);
bad_register_merge_target:
dm_unregister_target(&origin_target);
bad_register_origin_target:
dm_unregister_target(&snapshot_target);
bad_register_snapshot_target:
dm_exception_store_exit();
return r;
}
static void __exit dm_snapshot_exit(void)
{
dm_unregister_target(&snapshot_target);
dm_unregister_target(&origin_target);
dm_unregister_target(&merge_target);
exit_origin_hash();
kmem_cache_destroy(pending_cache);
kmem_cache_destroy(exception_cache);
dm_exception_store_exit();
}
/* Module hooks */
module_init(dm_snapshot_init);
module_exit(dm_snapshot_exit);
MODULE_DESCRIPTION(DM_NAME " snapshot target");
MODULE_AUTHOR("Joe Thornber");
MODULE_LICENSE("GPL");
MODULE_ALIAS("dm-snapshot-origin");
MODULE_ALIAS("dm-snapshot-merge");