/* * 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) { BUG_ON(index >= ps->exceptions_per_area); return ((struct disk_exception *) ps->area) + index; } static void read_exception(struct pstore *ps, uint32_t index, struct disk_exception *result) { struct disk_exception *e = get_exception(ps, index); /* copy it */ result->old_chunk = le64_to_cpu(e->old_chunk); result->new_chunk = le64_to_cpu(e->new_chunk); } static void write_exception(struct pstore *ps, uint32_t index, struct disk_exception *de) { struct disk_exception *e = get_exception(ps, index); /* copy it */ e->old_chunk = cpu_to_le64(de->old_chunk); e->new_chunk = cpu_to_le64(de->new_chunk); } /* * 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++) { read_exception(ps, i, &de); /* * 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; /* * 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; } for (i = 0; i < ps->callback_count; i++) { cb = ps->callbacks + i; cb->callback(cb->context, r == 0 ? 1 : 0); } ps->callback_count = 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; }