/*
* Copyright (C) 2001-2002 Sistina Software (UK) Limited.
* Copyright (C) 2006-2008 Red Hat GmbH
*
* This file is released under the GPL.
*/
#include "dm-exception-store.h"
#include <linux/ctype.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/vmalloc.h>
#include <linux/export.h>
#include <linux/slab.h>
#include <linux/dm-io.h>
#include <linux/dm-bufio.h>
#define DM_MSG_PREFIX "persistent snapshot"
#define DM_CHUNK_SIZE_DEFAULT_SECTORS 32 /* 16KB */
#define DM_PREFETCH_CHUNKS 12
/*-----------------------------------------------------------------
* Persistent snapshots, by persistent we mean that the snapshot
* will survive a reboot.
*---------------------------------------------------------------*/
/*
* We need to store a record of which parts of the origin have
* been copied to the snapshot device. The snapshot code
* requires that we copy exception chunks to chunk aligned areas
* of the COW store. It makes sense therefore, to store the
* metadata in chunk size blocks.
*
* There is no backward or forward compatibility implemented,
* snapshots with different disk versions than the kernel will
* not be usable. It is expected that "lvcreate" will blank out
* the start of a fresh COW device before calling the snapshot
* constructor.
*
* The first chunk of the COW device just contains the header.
* After this there is a chunk filled with exception metadata,
* followed by as many exception chunks as can fit in the
* metadata areas.
*
* All on disk structures are in little-endian format. The end
* of the exceptions info is indicated by an exception with a
* new_chunk of 0, which is invalid since it would point to the
* header chunk.
*/
/*
* Magic for persistent snapshots: "SnAp" - Feeble isn't it.
*/
#define SNAP_MAGIC 0x70416e53
/*
* The on-disk version of the metadata.
*/
#define SNAPSHOT_DISK_VERSION 1
#define NUM_SNAPSHOT_HDR_CHUNKS 1
struct disk_header {
__le32 magic;
/*
* Is this snapshot valid. There is no way of recovering
* an invalid snapshot.
*/
__le32 valid;
/*
* Simple, incrementing version. no backward
* compatibility.
*/
__le32 version;
/* In sectors */
__le32 chunk_size;
} __packed;
struct disk_exception {
__le64 old_chunk;
__le64 new_chunk;
} __packed;
struct core_exception {
uint64_t old_chunk;
uint64_t new_chunk;
};
struct commit_callback {
void (*callback)(void *, int success);
void *context;
};
/*
* The top level structure for a persistent exception store.
*/
struct pstore {
struct dm_exception_store *store;
int version;
int valid;
uint32_t exceptions_per_area;
/*
* Now that we have an asynchronous kcopyd there is no
* need for large chunk sizes, so it wont hurt to have a
* whole chunks worth of metadata in memory at once.
*/
void *area;
/*
* An area of zeros used to clear the next area.
*/
void *zero_area;
/*
* An area used for header. The header can be written
* concurrently with metadata (when invalidating the snapshot),
* so it needs a separate buffer.
*/
void *header_area;
/*
* Used to keep track of which metadata area the data in
* 'chunk' refers to.
*/
chunk_t current_area;
/*
* The next free chunk for an exception.
*
* When creating exceptions, all the chunks here and above are
* free. It holds the next chunk to be allocated. On rare
* occasions (e.g. after a system crash) holes can be left in
* the exception store because chunks can be committed out of
* order.
*
* When merging exceptions, it does not necessarily mean all the
* chunks here and above are free. It holds the value it would
* have held if all chunks had been committed in order of
* allocation. Consequently the value may occasionally be
* slightly too low, but since it's only used for 'status' and
* it can never reach its minimum value too early this doesn't
* matter.
*/
chunk_t next_free;
/*
* The index of next free exception in the current
* metadata area.
*/
uint32_t current_committed;
atomic_t pending_count;
uint32_t callback_count;
struct commit_callback *callbacks;
struct dm_io_client *io_client;
struct workqueue_struct *metadata_wq;
};
static int alloc_area(struct pstore *ps)
{
int r = -ENOMEM;
size_t len;
len = ps->store->chunk_size << SECTOR_SHIFT;
/*
* Allocate the chunk_size block of memory that will hold
* a single metadata area.
*/
ps->area = vmalloc(len);
if (!ps->area)
goto err_area;
ps->zero_area = vzalloc(len);
if (!ps->zero_area)
goto err_zero_area;
ps->header_area = vmalloc(len);
if (!ps->header_area)
goto err_header_area;
return 0;
err_header_area:
vfree(ps->zero_area);
err_zero_area:
vfree(ps->area);
err_area:
return r;
}
static void free_area(struct pstore *ps)
{
vfree(ps->area);
ps->area = NULL;
vfree(ps->zero_area);
ps->zero_area = NULL;
vfree(ps->header_area);
ps->header_area = NULL;
}
struct mdata_req {
struct dm_io_region *where;
struct dm_io_request *io_req;
struct work_struct work;
int result;
};
static void do_metadata(struct work_struct *work)
{
struct mdata_req *req = container_of(work, struct mdata_req, work);
req->result = dm_io(req->io_req, 1, req->where, NULL);
}
/*
* Read or write a chunk aligned and sized block of data from a device.
*/
static int chunk_io(struct pstore *ps, void *area, chunk_t chunk, int op,
int op_flags, int metadata)
{
struct dm_io_region where = {
.bdev = dm_snap_cow(ps->store->snap)->bdev,
.sector = ps->store->chunk_size * chunk,
.count = ps->store->chunk_size,
};
struct dm_io_request io_req = {
.bi_op = op,
.bi_op_flags = op_flags,
.mem.type = DM_IO_VMA,
.mem.ptr.vma = area,
.client = ps->io_client,
.notify.fn = NULL,
};
struct mdata_req req;
if (!metadata)
return dm_io(&io_req, 1, &where, NULL);
req.where = &where;
req.io_req = &io_req;
/*
* Issue the synchronous I/O from a different thread
* to avoid generic_make_request recursion.
*/
INIT_WORK_ONSTACK(&req.work, do_metadata);
queue_work(ps->metadata_wq, &req.work);
flush_workqueue(ps->metadata_wq);
destroy_work_on_stack(&req.work);
return req.result;
}
/*
* Convert a metadata area index to a chunk index.
*/
static chunk_t area_location(struct pstore *ps, chunk_t area)
{
return NUM_SNAPSHOT_HDR_CHUNKS + ((ps->exceptions_per_area + 1) * area);
}
static void skip_metadata(struct pstore *ps)
{
uint32_t stride = ps->exceptions_per_area + 1;
chunk_t next_free = ps->next_free;
if (sector_div(next_free, stride) == NUM_SNAPSHOT_HDR_CHUNKS)
ps->next_free++;
}
/*
* Read or write a metadata area. Remembering to skip the first
* chunk which holds the header.
*/
static int area_io(struct pstore *ps, int op, int op_flags)
{
int r;
chunk_t chunk;
chunk = area_location(ps, ps->current_area);
r = chunk_io(ps, ps->area, chunk, op, op_flags, 0);
if (r)
return r;
return 0;
}
static void zero_memory_area(struct pstore *ps)
{
memset(ps->area, 0, ps->store->chunk_size << SECTOR_SHIFT);
}
static int zero_disk_area(struct pstore *ps, chunk_t area)
{
return chunk_io(ps, ps->zero_area, area_location(ps, area),
REQ_OP_WRITE, 0, 0);
}
static int read_header(struct pstore *ps, int *new_snapshot)
{
int r;
struct disk_header *dh;
unsigned chunk_size;
int chunk_size_supplied = 1;
char *chunk_err;
/*
* Use default chunk size (or logical_block_size, if larger)
* if none supplied
*/
if (!ps->store->chunk_size) {
ps->store->chunk_size = max(DM_CHUNK_SIZE_DEFAULT_SECTORS,
bdev_logical_block_size(dm_snap_cow(ps->store->snap)->
bdev) >> 9);
ps->store->chunk_mask = ps->store->chunk_size - 1;
ps->store->chunk_shift = __ffs(ps->store->chunk_size);
chunk_size_supplied = 0;
}
ps->io_client = dm_io_client_create();
if (IS_ERR(ps->io_client))
return PTR_ERR(ps->io_client);
r = alloc_area(ps);
if (r)
return r;
r = chunk_io(ps, ps->header_area, 0, REQ_OP_READ, 0, 1);
if (r)
goto bad;
dh = ps->header_area;
if (le32_to_cpu(dh->magic) == 0) {
*new_snapshot = 1;
return 0;
}
if (le32_to_cpu(dh->magic) != SNAP_MAGIC) {
DMWARN("Invalid or corrupt snapshot");
r = -ENXIO;
goto bad;
}
*new_snapshot = 0;
ps->valid = le32_to_cpu(dh->valid);
ps->version = le32_to_cpu(dh->version);
chunk_size = le32_to_cpu(dh->chunk_size);
if (ps->store->chunk_size == chunk_size)
return 0;
if (chunk_size_supplied)
DMWARN("chunk size %u in device metadata overrides "
"table chunk size of %u.",
chunk_size, ps->store->chunk_size);
/* We had a bogus chunk_size. Fix stuff up. */
free_area(ps);
r = dm_exception_store_set_chunk_size(ps->store, chunk_size,
&chunk_err);
if (r) {
DMERR("invalid on-disk chunk size %u: %s.",
chunk_size, chunk_err);
return r;
}
r = alloc_area(ps);
return r;
bad:
free_area(ps);
return r;
}
static int write_header(struct pstore *ps)
{
struct disk_header *dh;
memset(ps->header_area, 0, ps->store->chunk_size << SECTOR_SHIFT);
dh = ps->header_area;
dh->magic = cpu_to_le32(SNAP_MAGIC);
dh->valid = cpu_to_le32(ps->valid);
dh->version = cpu_to_le32(ps->version);
dh->chunk_size = cpu_to_le32(ps->store->chunk_size);
return chunk_io(ps, ps->header_area, 0, REQ_OP_WRITE, 0, 1);
}
/*
* Access functions for the disk exceptions, these do the endian conversions.
*/
static struct disk_exception *get_exception(struct pstore *ps, void *ps_area,
uint32_t index)
{
BUG_ON(index >= ps->exceptions_per_area);
return ((struct disk_exception *) ps_area) + index;
}
static void read_exception(struct pstore *ps, void *ps_area,
uint32_t index, struct core_exception *result)
{
struct disk_exception *de = get_exception(ps, ps_area, index);
/* copy it */
result->old_chunk = le64_to_cpu(de->old_chunk);
result->new_chunk = le64_to_cpu(de->new_chunk);
}
static void write_exception(struct pstore *ps,
uint32_t index, struct core_exception *e)
{
struct disk_exception *de = get_exception(ps, ps->area, index);
/* copy it */
de->old_chunk = cpu_to_le64(e->old_chunk);
de->new_chunk = cpu_to_le64(e->new_chunk);
}
static void clear_exception(struct pstore *ps, uint32_t index)
{
struct disk_exception *de = get_exception(ps, ps->area, index);
/* clear it */
de->old_chunk = 0;
de->new_chunk = 0;
}
/*
* Registers the exceptions that are present in the current area.
* 'full' is filled in to indicate if the area has been
* filled.
*/
static int insert_exceptions(struct pstore *ps, void *ps_area,
int (*callback)(void *callback_context,
chunk_t old, chunk_t new),
void *callback_context,
int *full)
{
int r;
unsigned int i;
struct core_exception e;
/* presume the area is full */
*full = 1;
for (i = 0; i < ps->exceptions_per_area; i++) {
read_exception(ps, ps_area, i, &e);
/*
* If the new_chunk is pointing at the start of
* the COW device, where the first metadata area
* is we know that we've hit the end of the
* exceptions. Therefore the area is not full.
*/
if (e.new_chunk == 0LL) {
ps->current_committed = i;
*full = 0;
break;
}
/*
* Keep track of the start of the free chunks.
*/
if (ps->next_free <= e.new_chunk)
ps->next_free = e.new_chunk + 1;
/*
* Otherwise we add the exception to the snapshot.
*/
r = callback(callback_context, e.old_chunk, e.new_chunk);
if (r)
return r;
}
return 0;
}
static int read_exceptions(struct pstore *ps,
int (*callback)(void *callback_context, chunk_t old,
chunk_t new),
void *callback_context)
{
int r, full = 1;
struct dm_bufio_client *client;
chunk_t prefetch_area = 0;
client = dm_bufio_client_create(dm_snap_cow(ps->store->snap)->bdev,
ps->store->chunk_size << SECTOR_SHIFT,
1, 0, NULL, NULL);
if (IS_ERR(client))
return PTR_ERR(client);
/*
* Setup for one current buffer + desired readahead buffers.
*/
dm_bufio_set_minimum_buffers(client, 1 + DM_PREFETCH_CHUNKS);
/*
* Keeping reading chunks and inserting exceptions until
* we find a partially full area.
*/
for (ps->current_area = 0; full; ps->current_area++) {
struct dm_buffer *bp;
void *area;
chunk_t chunk;
if (unlikely(prefetch_area < ps->current_area))
prefetch_area = ps->current_area;
if (DM_PREFETCH_CHUNKS) do {
chunk_t pf_chunk = area_location(ps, prefetch_area);
if (unlikely(pf_chunk >= dm_bufio_get_device_size(client)))
break;
dm_bufio_prefetch(client, pf_chunk, 1);
prefetch_area++;
if (unlikely(!prefetch_area))
break;
} while (prefetch_area <= ps->current_area + DM_PREFETCH_CHUNKS);
chunk = area_location(ps, ps->current_area);
area = dm_bufio_read(client, chunk, &bp);
if (IS_ERR(area)) {
r = PTR_ERR(area);
goto ret_destroy_bufio;
}
r = insert_exceptions(ps, area, callback, callback_context,
&full);
if (!full)
memcpy(ps->area, area, ps->store->chunk_size << SECTOR_SHIFT);
dm_bufio_release(bp);
dm_bufio_forget(client, chunk);
if (unlikely(r))
goto ret_destroy_bufio;
}
ps->current_area--;
skip_metadata(ps);
r = 0;
ret_destroy_bufio:
dm_bufio_client_destroy(client);
return r;
}
static struct pstore *get_info(struct dm_exception_store *store)
{
return (struct pstore *) store->context;
}
static void persistent_usage(struct dm_exception_store *store,
sector_t *total_sectors,
sector_t *sectors_allocated,
sector_t *metadata_sectors)
{
struct pstore *ps = get_info(store);
*sectors_allocated = ps->next_free * store->chunk_size;
*total_sectors = get_dev_size(dm_snap_cow(store->snap)->bdev);
/*
* First chunk is the fixed header.
* Then there are (ps->current_area + 1) metadata chunks, each one
* separated from the next by ps->exceptions_per_area data chunks.
*/
*metadata_sectors = (ps->current_area + 1 + NUM_SNAPSHOT_HDR_CHUNKS) *
store->chunk_size;
}
static void persistent_dtr(struct dm_exception_store *store)
{
struct pstore *ps = get_info(store);
destroy_workqueue(ps->metadata_wq);
/* Created in read_header */
if (ps->io_client)
dm_io_client_destroy(ps->io_client);
free_area(ps);
/* Allocated in persistent_read_metadata */
vfree(ps->callbacks);
kfree(ps);
}
static int persistent_read_metadata(struct dm_exception_store *store,
int (*callback)(void *callback_context,
chunk_t old, chunk_t new),
void *callback_context)
{
int r, uninitialized_var(new_snapshot);
struct pstore *ps = get_info(store);
/*
* Read the snapshot header.
*/
r = read_header(ps, &new_snapshot);
if (r)
return r;
/*
* Now we know correct chunk_size, complete the initialisation.
*/
ps->exceptions_per_area = (ps->store->chunk_size << SECTOR_SHIFT) /
sizeof(struct disk_exception);
ps->callbacks = dm_vcalloc(ps->exceptions_per_area,
sizeof(*ps->callbacks));
if (!ps->callbacks)
return -ENOMEM;
/*
* Do we need to setup a new snapshot ?
*/
if (new_snapshot) {
r = write_header(ps);
if (r) {
DMWARN("write_header failed");
return r;
}
ps->current_area = 0;
zero_memory_area(ps);
r = zero_disk_area(ps, 0);
if (r)
DMWARN("zero_disk_area(0) failed");
return r;
}
/*
* Sanity checks.
*/
if (ps->version != SNAPSHOT_DISK_VERSION) {
DMWARN("unable to handle snapshot disk version %d",
ps->version);
return -EINVAL;
}
/*
* Metadata are valid, but snapshot is invalidated
*/
if (!ps->valid)
return 1;
/*
* Read the metadata.
*/
r = read_exceptions(ps, callback, callback_context);
return r;
}
static int persistent_prepare_exception(struct dm_exception_store *store,
struct dm_exception *e)
{
struct pstore *ps = get_info(store);
sector_t size = get_dev_size(dm_snap_cow(store->snap)->bdev);
/* Is there enough room ? */
if (size < ((ps->next_free + 1) * store->chunk_size))
return -ENOSPC;
e->new_chunk = ps->next_free;
/*
* Move onto the next free pending, making sure to take
* into account the location of the metadata chunks.
*/
ps->next_free++;
skip_metadata(ps);
atomic_inc(&ps->pending_count);
return 0;
}
static void persistent_commit_exception(struct dm_exception_store *store,
struct dm_exception *e, int valid,
void (*callback) (void *, int success),
void *callback_context)
{
unsigned int i;
struct pstore *ps = get_info(store);
struct core_exception ce;
struct commit_callback *cb;
if (!valid)
ps->valid = 0;
ce.old_chunk = e->old_chunk;
ce.new_chunk = e->new_chunk;
write_exception(ps, ps->current_committed++, &ce);
/*
* Add the callback to the back of the array. This code
* is the only place where the callback array is
* manipulated, and we know that it will never be called
* multiple times concurrently.
*/
cb = ps->callbacks + ps->callback_count++;
cb->callback = callback;
cb->context = callback_context;
/*
* If there are exceptions in flight and we have not yet
* filled this metadata area there's nothing more to do.
*/
if (!atomic_dec_and_test(&ps->pending_count) &&
(ps->current_committed != ps->exceptions_per_area))
return;
/*
* If we completely filled the current area, then wipe the next one.
*/
if ((ps->current_committed == ps->exceptions_per_area) &&
zero_disk_area(ps, ps->current_area + 1))
ps->valid = 0;
/*
* Commit exceptions to disk.
*/
if (ps->valid && area_io(ps, REQ_OP_WRITE,
REQ_PREFLUSH | REQ_FUA | REQ_SYNC))
ps->valid = 0;
/*
* Advance to the next area if this one is full.
*/
if (ps->current_committed == ps->exceptions_per_area) {
ps->current_committed = 0;
ps->current_area++;
zero_memory_area(ps);
}
for (i = 0; i < ps->callback_count; i++) {
cb = ps->callbacks + i;
cb->callback(cb->context, ps->valid);
}
ps->callback_count = 0;
}
static int persistent_prepare_merge(struct dm_exception_store *store,
chunk_t *last_old_chunk,
chunk_t *last_new_chunk)
{
struct pstore *ps = get_info(store);
struct core_exception ce;
int nr_consecutive;
int r;
/*
* When current area is empty, move back to preceding area.
*/
if (!ps->current_committed) {
/*
* Have we finished?
*/
if (!ps->current_area)
return 0;
ps->current_area--;
r = area_io(ps, REQ_OP_READ, 0);
if (r < 0)
return r;
ps->current_committed = ps->exceptions_per_area;
}
read_exception(ps, ps->area, ps->current_committed - 1, &ce);
*last_old_chunk = ce.old_chunk;
*last_new_chunk = ce.new_chunk;
/*
* Find number of consecutive chunks within the current area,
* working backwards.
*/
for (nr_consecutive = 1; nr_consecutive < ps->current_committed;
nr_consecutive++) {
read_exception(ps, ps->area,
ps->current_committed - 1 - nr_consecutive, &ce);
if (ce.old_chunk != *last_old_chunk - nr_consecutive ||
ce.new_chunk != *last_new_chunk - nr_consecutive)
break;
}
return nr_consecutive;
}
static int persistent_commit_merge(struct dm_exception_store *store,
int nr_merged)
{
int r, i;
struct pstore *ps = get_info(store);
BUG_ON(nr_merged > ps->current_committed);
for (i = 0; i < nr_merged; i++)
clear_exception(ps, ps->current_committed - 1 - i);
r = area_io(ps, REQ_OP_WRITE, REQ_PREFLUSH | REQ_FUA);
if (r < 0)
return r;
ps->current_committed -= nr_merged;
/*
* At this stage, only persistent_usage() uses ps->next_free, so
* we make no attempt to keep ps->next_free strictly accurate
* as exceptions may have been committed out-of-order originally.
* Once a snapshot has become merging, we set it to the value it
* would have held had all the exceptions been committed in order.
*
* ps->current_area does not get reduced by prepare_merge() until
* after commit_merge() has removed the nr_merged previous exceptions.
*/
ps->next_free = area_location(ps, ps->current_area) +
ps->current_committed + 1;
return 0;
}
static void persistent_drop_snapshot(struct dm_exception_store *store)
{
struct pstore *ps = get_info(store);
ps->valid = 0;
if (write_header(ps))
DMWARN("write header failed");
}
static int persistent_ctr(struct dm_exception_store *store, char *options)
{
struct pstore *ps;
int r;
/* allocate the pstore */
ps = kzalloc(sizeof(*ps), GFP_KERNEL);
if (!ps)
return -ENOMEM;
ps->store = store;
ps->valid = 1;
ps->version = SNAPSHOT_DISK_VERSION;
ps->area = NULL;
ps->zero_area = NULL;
ps->header_area = NULL;
ps->next_free = NUM_SNAPSHOT_HDR_CHUNKS + 1; /* header and 1st area */
ps->current_committed = 0;
ps->callback_count = 0;
atomic_set(&ps->pending_count, 0);
ps->callbacks = NULL;
ps->metadata_wq = alloc_workqueue("ksnaphd", WQ_MEM_RECLAIM, 0);
if (!ps->metadata_wq) {
DMERR("couldn't start header metadata update thread");
r = -ENOMEM;
goto err_workqueue;
}
if (options) {
char overflow = toupper(options[0]);
if (overflow == 'O')
store->userspace_supports_overflow = true;
else {
DMERR("Unsupported persistent store option: %s", options);
r = -EINVAL;
goto err_options;
}
}
store->context = ps;
return 0;
err_options:
destroy_workqueue(ps->metadata_wq);
err_workqueue:
kfree(ps);
return r;
}
static unsigned persistent_status(struct dm_exception_store *store,
status_type_t status, char *result,
unsigned maxlen)
{
unsigned sz = 0;
switch (status) {
case STATUSTYPE_INFO:
break;
case STATUSTYPE_TABLE:
DMEMIT(" %s %llu", store->userspace_supports_overflow ? "PO" : "P",
(unsigned long long)store->chunk_size);
}
return sz;
}
static struct dm_exception_store_type _persistent_type = {
.name = "persistent",
.module = THIS_MODULE,
.ctr = persistent_ctr,
.dtr = persistent_dtr,
.read_metadata = persistent_read_metadata,
.prepare_exception = persistent_prepare_exception,
.commit_exception = persistent_commit_exception,
.prepare_merge = persistent_prepare_merge,
.commit_merge = persistent_commit_merge,
.drop_snapshot = persistent_drop_snapshot,
.usage = persistent_usage,
.status = persistent_status,
};
static struct dm_exception_store_type _persistent_compat_type = {
.name = "P",
.module = THIS_MODULE,
.ctr = persistent_ctr,
.dtr = persistent_dtr,
.read_metadata = persistent_read_metadata,
.prepare_exception = persistent_prepare_exception,
.commit_exception = persistent_commit_exception,
.prepare_merge = persistent_prepare_merge,
.commit_merge = persistent_commit_merge,
.drop_snapshot = persistent_drop_snapshot,
.usage = persistent_usage,
.status = persistent_status,
};
int dm_persistent_snapshot_init(void)
{
int r;
r = dm_exception_store_type_register(&_persistent_type);
if (r) {
DMERR("Unable to register persistent exception store type");
return r;
}
r = dm_exception_store_type_register(&_persistent_compat_type);
if (r) {
DMERR("Unable to register old-style persistent exception "
"store type");
dm_exception_store_type_unregister(&_persistent_type);
return r;
}
return r;
}
void dm_persistent_snapshot_exit(void)
{
dm_exception_store_type_unregister(&_persistent_type);
dm_exception_store_type_unregister(&_persistent_compat_type);
}
