/*
* dm-snapshot.c
*
* Copyright (C) 2001-2002 Sistina Software (UK) Limited.
*
* This file is released under the GPL.
*/
#include "dm.h"
#include "dm-snap.h"
#include "dm-io.h"
#include "kcopyd.h"
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/vmalloc.h>
#include <linux/slab.h>
/*-----------------------------------------------------------------
* 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
struct disk_header {
uint32_t magic;
/*
* Is this snapshot valid. There is no way of recovering
* an invalid snapshot.
*/
uint32_t valid;
/*
* Simple, incrementing version. no backward
* compatibility.
*/
uint32_t version;
/* In sectors */
uint32_t chunk_size;
};
struct disk_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_snapshot *snap; /* up pointer to my snapshot */
int version;
int valid;
uint32_t chunk_size;
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;
/*
* Used to keep track of which metadata area the data in
* 'chunk' refers to.
*/
uint32_t current_area;
/*
* The next free chunk for an exception.
*/
uint32_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;
};
static inline unsigned int sectors_to_pages(unsigned int sectors)
{
return sectors / (PAGE_SIZE >> 9);
}
static int alloc_area(struct pstore *ps)
{
int r = -ENOMEM;
size_t len;
len = ps->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)
return r;
return 0;
}
static void free_area(struct pstore *ps)
{
vfree(ps->area);
}
/*
* Read or write a chunk aligned and sized block of data from a device.
*/
static int chunk_io(struct pstore *ps, uint32_t chunk, int rw)
{
struct io_region where;
unsigned long bits;
where.bdev = ps->snap->cow->bdev;
where.sector = ps->chunk_size * chunk;
where.count = ps->chunk_size;
return dm_io_sync_vm(1, &where, rw, ps->area, &bits);
}
/*
* Read or write a metadata area. Remembering to skip the first
* chunk which holds the header.
*/
static int area_io(struct pstore *ps, uint32_t area, int rw)
{
int r;
uint32_t chunk;
/* convert a metadata area index to a chunk index */
chunk = 1 + ((ps->exceptions_per_area + 1) * area);
r = chunk_io(ps, chunk, rw);
if (r)
return r;
ps->current_area = area;
return 0;
}
static int zero_area(struct pstore *ps, uint32_t area)
{
memset(ps->area, 0, ps->chunk_size << SECTOR_SHIFT);
return area_io(ps, area, WRITE);
}
static int read_header(struct pstore *ps, int *new_snapshot)
{
int r;
struct disk_header *dh;
r = chunk_io(ps, 0, READ);
if (r)
return r;
dh = (struct disk_header *) ps->area;
if (le32_to_cpu(dh->magic) == 0) {
*new_snapshot = 1;
} else if (le32_to_cpu(dh->magic) == SNAP_MAGIC) {
*new_snapshot = 0;
ps->valid = le32_to_cpu(dh->valid);
ps->version = le32_to_cpu(dh->version);
ps->chunk_size = le32_to_cpu(dh->chunk_size);
} else {
DMWARN("Invalid/corrupt snapshot");
r = -ENXIO;
}
return r;
}
static int write_header(struct pstore *ps)
{
struct disk_header *dh;
memset(ps->area, 0, ps->chunk_size << SECTOR_SHIFT);
dh = (struct disk_header *) ps->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->chunk_size);
return chunk_io(ps, 0, WRITE);
}
/*
* Access functions for the disk exceptions, these do the endian conversions.
*/
static struct disk_exception *get_exception(struct pstore *ps, uint32_t index)
{
if (index >= ps->exceptions_per_area)
return NULL;
return ((struct disk_exception *) ps->area) + index;
}
static int read_exception(struct pstore *ps,
uint32_t index, struct disk_exception *result)
{
struct disk_exception *e;
e = get_exception(ps, index);
if (!e)
return -EINVAL;
/* copy it */
result->old_chunk = le64_to_cpu(e->old_chunk);
result->new_chunk = le64_to_cpu(e->new_chunk);
return 0;
}
static int write_exception(struct pstore *ps,
uint32_t index, struct disk_exception *de)
{
struct disk_exception *e;
e = get_exception(ps, index);
if (!e)
return -EINVAL;
/* copy it */
e->old_chunk = cpu_to_le64(de->old_chunk);
e->new_chunk = cpu_to_le64(de->new_chunk);
return 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, int *full)
{
int r;
unsigned int i;
struct disk_exception de;
/* presume the area is full */
*full = 1;
for (i = 0; i < ps->exceptions_per_area; i++) {
r = read_exception(ps, i, &de);
if (r)
return r;
/*
* 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 (de.new_chunk == 0LL) {
ps->current_committed = i;
*full = 0;
break;
}
/*
* Keep track of the start of the free chunks.
*/
if (ps->next_free <= de.new_chunk)
ps->next_free = de.new_chunk + 1;
/*
* Otherwise we add the exception to the snapshot.
*/
r = dm_add_exception(ps->snap, de.old_chunk, de.new_chunk);
if (r)
return r;
}
return 0;
}
static int read_exceptions(struct pstore *ps)
{
uint32_t area;
int r, full = 1;
/*
* Keeping reading chunks and inserting exceptions until
* we find a partially full area.
*/
for (area = 0; full; area++) {
r = area_io(ps, area, READ);
if (r)
return r;
r = insert_exceptions(ps, &full);
if (r)
return r;
}
return 0;
}
static inline struct pstore *get_info(struct exception_store *store)
{
return (struct pstore *) store->context;
}
static void persistent_fraction_full(struct exception_store *store,
sector_t *numerator, sector_t *denominator)
{
*numerator = get_info(store)->next_free * store->snap->chunk_size;
*denominator = get_dev_size(store->snap->cow->bdev);
}
static void persistent_destroy(struct exception_store *store)
{
struct pstore *ps = get_info(store);
dm_io_put(sectors_to_pages(ps->chunk_size));
vfree(ps->callbacks);
free_area(ps);
kfree(ps);
}
static int persistent_read_metadata(struct exception_store *store)
{
int r, new_snapshot;
struct pstore *ps = get_info(store);
/*
* Read the snapshot header.
*/
r = read_header(ps, &new_snapshot);
if (r)
return r;
/*
* Do we need to setup a new snapshot ?
*/
if (new_snapshot) {
r = write_header(ps);
if (r) {
DMWARN("write_header failed");
return r;
}
r = zero_area(ps, 0);
if (r) {
DMWARN("zero_area(0) failed");
return r;
}
} else {
/*
* Sanity checks.
*/
if (!ps->valid) {
DMWARN("snapshot is marked invalid");
return -EINVAL;
}
if (ps->version != SNAPSHOT_DISK_VERSION) {
DMWARN("unable to handle snapshot disk version %d",
ps->version);
return -EINVAL;
}
/*
* Read the metadata.
*/
r = read_exceptions(ps);
if (r)
return r;
}
return 0;
}
static int persistent_prepare(struct exception_store *store,
struct exception *e)
{
struct pstore *ps = get_info(store);
uint32_t stride;
sector_t size = get_dev_size(store->snap->cow->bdev);
/* Is there enough room ? */
if (size < ((ps->next_free + 1) * store->snap->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.
*/
stride = (ps->exceptions_per_area + 1);
if ((++ps->next_free % stride) == 1)
ps->next_free++;
atomic_inc(&ps->pending_count);
return 0;
}
static void persistent_commit(struct exception_store *store,
struct exception *e,
void (*callback) (void *, int success),
void *callback_context)
{
int r;
unsigned int i;
struct pstore *ps = get_info(store);
struct disk_exception de;
struct commit_callback *cb;
de.old_chunk = e->old_chunk;
de.new_chunk = e->new_chunk;
write_exception(ps, ps->current_committed++, &de);
/*
* 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 no more exceptions in flight, or we have
* filled this metadata area we commit the exceptions to
* disk.
*/
if (atomic_dec_and_test(&ps->pending_count) ||
(ps->current_committed == ps->exceptions_per_area)) {
r = area_io(ps, ps->current_area, WRITE);
if (r)
ps->valid = 0;
for (i = 0; i < ps->callback_count; i++) {
cb = ps->callbacks + i;
cb->callback(cb->context, r == 0 ? 1 : 0);
}
ps->callback_count = 0;
}
/*
* Have we completely filled the current area ?
*/
if (ps->current_committed == ps->exceptions_per_area) {
ps->current_committed = 0;
r = zero_area(ps, ps->current_area + 1);
if (r)
ps->valid = 0;
}
}
static void persistent_drop(struct exception_store *store)
{
struct pstore *ps = get_info(store);
ps->valid = 0;
if (write_header(ps))
DMWARN("write header failed");
}
int dm_create_persistent(struct exception_store *store, uint32_t chunk_size)
{
int r;
struct pstore *ps;
r = dm_io_get(sectors_to_pages(chunk_size));
if (r)
return r;
/* allocate the pstore */
ps = kmalloc(sizeof(*ps), GFP_KERNEL);
if (!ps) {
r = -ENOMEM;
goto bad;
}
ps->snap = store->snap;
ps->valid = 1;
ps->version = SNAPSHOT_DISK_VERSION;
ps->chunk_size = chunk_size;
ps->exceptions_per_area = (chunk_size << SECTOR_SHIFT) /
sizeof(struct disk_exception);
ps->next_free = 2; /* skipping the header and first area */
ps->current_committed = 0;
r = alloc_area(ps);
if (r)
goto bad;
/*
* Allocate space for all the callbacks.
*/
ps->callback_count = 0;
atomic_set(&ps->pending_count, 0);
ps->callbacks = dm_vcalloc(ps->exceptions_per_area,
sizeof(*ps->callbacks));
if (!ps->callbacks) {
r = -ENOMEM;
goto bad;
}
store->destroy = persistent_destroy;
store->read_metadata = persistent_read_metadata;
store->prepare_exception = persistent_prepare;
store->commit_exception = persistent_commit;
store->drop_snapshot = persistent_drop;
store->fraction_full = persistent_fraction_full;
store->context = ps;
return 0;
bad:
dm_io_put(sectors_to_pages(chunk_size));
if (ps && ps->area)
free_area(ps);
kfree(ps);
return r;
}
/*-----------------------------------------------------------------
* Implementation of the store for non-persistent snapshots.
*---------------------------------------------------------------*/
struct transient_c {
sector_t next_free;
};
static void transient_destroy(struct exception_store *store)
{
kfree(store->context);
}
static int transient_read_metadata(struct exception_store *store)
{
return 0;
}
static int transient_prepare(struct exception_store *store, struct exception *e)
{
struct transient_c *tc = (struct transient_c *) store->context;
sector_t size = get_dev_size(store->snap->cow->bdev);
if (size < (tc->next_free + store->snap->chunk_size))
return -1;
e->new_chunk = sector_to_chunk(store->snap, tc->next_free);
tc->next_free += store->snap->chunk_size;
return 0;
}
static void transient_commit(struct exception_store *store,
struct exception *e,
void (*callback) (void *, int success),
void *callback_context)
{
/* Just succeed */
callback(callback_context, 1);
}
static void transient_fraction_full(struct exception_store *store,
sector_t *numerator, sector_t *denominator)
{
*numerator = ((struct transient_c *) store->context)->next_free;
*denominator = get_dev_size(store->snap->cow->bdev);
}
int dm_create_transient(struct exception_store *store,
struct dm_snapshot *s, int blocksize)
{
struct transient_c *tc;
memset(store, 0, sizeof(*store));
store->destroy = transient_destroy;
store->read_metadata = transient_read_metadata;
store->prepare_exception = transient_prepare;
store->commit_exception = transient_commit;
store->fraction_full = transient_fraction_full;
store->snap = s;
tc = kmalloc(sizeof(struct transient_c), GFP_KERNEL);
if (!tc)
return -ENOMEM;
tc->next_free = 0;
store->context = tc;
return 0;
}
