[PATCH] dm snapshot: allow zero chunk_size

[mirror_ubuntu-jammy-kernel.git] / drivers / md / dm-exception-store.c

/*
 * 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>

#define DM_MSG_PREFIX "snapshots"
#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;

        /*
         * 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->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;

        return 0;
}

static void free_area(struct pstore *ps)
{
        vfree(ps->area);
        ps->area = NULL;
}

/*
 * 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->snap->chunk_size * chunk;
        where.count = ps->snap->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->snap->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;
        chunk_t chunk_size;
        int chunk_size_supplied = 1;

        /*
         * Use default chunk size (or hardsect_size, if larger) if none supplied
         */
        if (!ps->snap->chunk_size) {
                ps->snap->chunk_size = max(DM_CHUNK_SIZE_DEFAULT_SECTORS,
                    bdev_hardsect_size(ps->snap->cow->bdev) >> 9);
                ps->snap->chunk_mask = ps->snap->chunk_size - 1;
                ps->snap->chunk_shift = ffs(ps->snap->chunk_size) - 1;
                chunk_size_supplied = 0;
        }

        r = dm_io_get(sectors_to_pages(ps->snap->chunk_size));
        if (r)
                return r;

        r = alloc_area(ps);
        if (r)
                goto bad1;

        r = chunk_io(ps, 0, READ);
        if (r)
                goto bad2;

        dh = (struct disk_header *) ps->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 bad2;
        }

        *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 (!chunk_size_supplied || ps->snap->chunk_size == chunk_size)
                return 0;

        DMWARN("chunk size %llu in device metadata overrides "
               "table chunk size of %llu.",
               (unsigned long long)chunk_size,
               (unsigned long long)ps->snap->chunk_size);

        /* We had a bogus chunk_size. Fix stuff up. */
        dm_io_put(sectors_to_pages(ps->snap->chunk_size));
        free_area(ps);

        ps->snap->chunk_size = chunk_size;
        ps->snap->chunk_mask = chunk_size - 1;
        ps->snap->chunk_shift = ffs(chunk_size) - 1;

        r = dm_io_get(sectors_to_pages(chunk_size));
        if (r)
                return r;

        r = alloc_area(ps);
        if (r)
                goto bad1;

        return 0;

bad2:
        free_area(ps);
bad1:
        dm_io_put(sectors_to_pages(ps->snap->chunk_size));
        return r;
}

static int write_header(struct pstore *ps)
{
        struct disk_header *dh;

        memset(ps->area, 0, ps->snap->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->snap->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->snap->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;

        /*
         * Now we know correct chunk_size, complete the initialisation.
         */
        ps->exceptions_per_area = (ps->snap->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;
                }

                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)
{
        struct pstore *ps;

        /* allocate the pstore */
        ps = kmalloc(sizeof(*ps), GFP_KERNEL);
        if (!ps)
                return -ENOMEM;

        ps->snap = store->snap;
        ps->valid = 1;
        ps->version = SNAPSHOT_DISK_VERSION;
        ps->area = NULL;
        ps->next_free = 2;      /* skipping the header and first area */
        ps->current_committed = 0;

        ps->callback_count = 0;
        atomic_set(&ps->pending_count, 0);
        ps->callbacks = NULL;

        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;
}

/*-----------------------------------------------------------------
 * 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 transient_c *tc;

        store->destroy = transient_destroy;
        store->read_metadata = transient_read_metadata;
        store->prepare_exception = transient_prepare;
        store->commit_exception = transient_commit;
        store->drop_snapshot = NULL;
        store->fraction_full = transient_fraction_full;

        tc = kmalloc(sizeof(struct transient_c), GFP_KERNEL);
        if (!tc)
                return -ENOMEM;

        tc->next_free = 0;
        store->context = tc;

        return 0;
}