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/*
* 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 "dm-snap.h"
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/vmalloc.h>
#include <linux/slab.h>
#include <linux/dm-io.h>
#define DM_MSG_PREFIX "persistent snapshot"
#define DM_CHUNK_SIZE_DEFAULT_SECTORS 32 /* 16KB */
/*-----------------------------------------------------------------
* 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 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;
/*
* 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.
*/
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 unsigned sectors_to_pages(unsigned sectors)
{
return DIV_ROUND_UP(sectors, PAGE_SIZE >> 9);
}
static int alloc_area(struct pstore *ps)
{
int r = -ENOMEM;
size_t len;
len = ps->snap->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;
ps->zero_area = vmalloc(len);
if (!ps->zero_area) {
vfree(ps->area);
return r;
}
memset(ps->zero_area, 0, len);
return 0;
}
static void free_area(struct pstore *ps)
{
vfree(ps->area);
ps->area = NULL;
vfree(ps->zero_area);
ps->zero_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, chunk_t chunk, int rw, int metadata)
{
struct dm_io_region where = {
.bdev = ps->snap->cow->bdev,
.sector = ps->snap->chunk_size * chunk,
.count = ps->snap->chunk_size,
};
struct dm_io_request io_req = {
.bi_rw = rw,
.mem.type = DM_IO_VMA,
.mem.ptr.vma = ps->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(&req.work, do_metadata);
queue_work(ps->metadata_wq, &req.work);
flush_workqueue(ps->metadata_wq);
return req.result;
}
/*
* Convert a metadata area index to a chunk index.
*/
static chunk_t area_location(struct pstore *ps, chunk_t area)
{
return 1 + ((ps->exceptions_per_area + 1) * area);
}
/*
* Read or write a metadata area. Remembering to skip the first
* chunk which holds the header.
*/
static int area_io(struct pstore *ps, int rw)
{
int r;
chunk_t chunk;
chunk = area_location(ps, ps->current_area);
r = chunk_io(ps, chunk, rw, 0);
if (r)
return r;
return 0;
}
static void zero_memory_area(struct pstore *ps)
{
memset(ps->area, 0, ps->snap->chunk_size << SECTOR_SHIFT);
}
static int zero_disk_area(struct pstore *ps, chunk_t area)
{
struct dm_io_region where = {
.bdev = ps->snap->cow->bdev,
.sector = ps->snap->chunk_size * area_location(ps, area),
.count = ps->snap->chunk_size,
};
struct dm_io_request io_req = {
.bi_rw = WRITE,
.mem.type = DM_IO_VMA,
.mem.ptr.vma = ps->zero_area,
.client = ps->io_client,
.notify.fn = NULL,
};
return dm_io(&io_req, 1, &where, NULL);
}
static int read_header(struct pstore *ps, int *new_snapshot)
{
int
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