/* * 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 32U /* 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); }