diff options
| -rw-r--r-- | block/qcow2-refcount.c | 310 |
1 files changed, 222 insertions, 88 deletions
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c index 933311c5ec..f714ca2df7 100644 --- a/block/qcow2-refcount.c +++ b/block/qcow2-refcount.c @@ -27,7 +27,7 @@ #include "block/qcow2.h" static int64_t alloc_clusters_noref(BlockDriverState *bs, int64_t size); -static int update_refcount(BlockDriverState *bs, +static int QEMU_WARN_UNUSED_RESULT update_refcount(BlockDriverState *bs, int64_t offset, int64_t length, int addend); @@ -141,114 +141,248 @@ static unsigned int next_refcount_table_size(BDRVQcowState *s, return refcount_table_clusters << (s->cluster_bits - 3); } -static int grow_refcount_table(BlockDriverState *bs, int min_size) + +/* Checks if two offsets are described by the same refcount block */ +static int in_same_refcount_block(BDRVQcowState *s, uint64_t offset_a, + uint64_t offset_b) +{ + uint64_t block_a = offset_a >> (2 * s->cluster_bits - REFCOUNT_SHIFT); + uint64_t block_b = offset_b >> (2 * s->cluster_bits - REFCOUNT_SHIFT); + + return (block_a == block_b); +} + +/* + * Loads a refcount block. If it doesn't exist yet, it is allocated first + * (including growing the refcount table if needed). + * + * Returns the offset of the refcount block on success or -errno in error case + */ +static int64_t alloc_refcount_block(BlockDriverState *bs, int64_t cluster_index) { BDRVQcowState *s = bs->opaque; - int new_table_size, new_table_size2, refcount_table_clusters, i, ret; - uint64_t *new_table; - int64_t table_offset; - uint8_t data[12]; - int old_table_size; - int64_t old_table_offset; + unsigned int refcount_table_index; + int ret; + + /* Find the refcount block for the given cluster */ + refcount_table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT); + + if (refcount_table_index < s->refcount_table_size) { + + uint64_t refcount_block_offset = + s->refcount_table[refcount_table_index]; + + /* If it's already there, we're done */ + if (refcount_block_offset) { + if (refcount_block_offset != s->refcount_block_cache_offset) { + ret = load_refcount_block(bs, refcount_block_offset); + if (ret < 0) { + return ret; + } + } + return refcount_block_offset; + } + } + + /* + * If we came here, we need to allocate something. Something is at least + * a cluster for the new refcount block. It may also include a new refcount + * table if the old refcount table is too small. + * + * Note that allocating clusters here needs some special care: + * + * - We can't use the normal qcow2_alloc_clusters(), it would try to + * increase the refcount and very likely we would end up with an endless + * recursion. Instead we must place the refcount blocks in a way that + * they can describe them themselves. + * + * - We need to consider that at this point we are inside update_refcounts + * and doing the initial refcount increase. This means that some clusters + * have already been allocated by the caller, but their refcount isn't + * accurate yet. free_cluster_index tells us where this allocation ends + * as long as we don't overwrite it by freeing clusters. + * + * - alloc_clusters_noref and qcow2_free_clusters may load a different + * refcount block into the cache + */ + + if (cache_refcount_updates) { + ret = write_refcount_block(s); + if (ret < 0) { + return ret; + } + } + + /* Allocate the refcount block itself and mark it as used */ + uint64_t new_block = alloc_clusters_noref(bs, s->cluster_size); + memset(s->refcount_block_cache, 0, s->cluster_size); + s->refcount_block_cache_offset = new_block; - if (min_size <= s->refcount_table_size) - return 0; - /* compute new table size */ - new_table_size = next_refcount_table_size(s, min_size); #ifdef DEBUG_ALLOC2 - printf("grow_refcount_table from %d to %d\n", - s->refcount_table_size, - new_table_size); + fprintf(stderr, "qcow2: Allocate refcount block %d for %" PRIx64 + " at %" PRIx64 "\n", + refcount_table_index, cluster_index << s->cluster_bits, new_block); #endif - new_table_size2 = new_table_size * sizeof(uint64_t); - new_table = qemu_mallocz(new_table_size2); + + if (in_same_refcount_block(s, new_block, cluster_index << s->cluster_bits)) { + /* The block describes itself, need to update the cache */ + int block_index = (new_block >> s->cluster_bits) & + ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1); + s->refcount_block_cache[block_index] = cpu_to_be16(1); + } else { + /* Described somewhere else. This can recurse at most twice before we + * arrive at a block that describes itself. */ + ret = update_refcount(bs, new_block, s->cluster_size, 1); + if (ret < 0) { + goto fail_block; + } + } + + /* Now the new refcount block needs to be written to disk */ + ret = bdrv_pwrite(s->hd, new_block, s->refcount_block_cache, + s->cluster_size); + if (ret < 0) { + goto fail_block; + } + + /* If the refcount table is big enough, just hook the block up there */ + if (refcount_table_index < s->refcount_table_size) { + uint64_t data64 = cpu_to_be64(new_block); + ret = bdrv_pwrite(s->hd, + s->refcount_table_offset + refcount_table_index * sizeof(uint64_t), + &data64, sizeof(data64)); + if (ret < 0) { + goto fail_block; + } + + s->refcount_table[refcount_table_index] = new_block; + return new_block; + } + + /* + * If we come here, we need to grow the refcount table. Again, a new + * refcount table needs some space and we can't simply allocate to avoid + * endless recursion. + * + * Therefore let's grab new refcount blocks at the end of the image, which + * will describe themselves and the new refcount table. This way we can + * reference them only in the new table and do the switch to the new + * refcount table at once without producing an inconsistent state in + * between. + */ + /* Calculate the number of refcount blocks needed so far */ + uint64_t refcount_block_clusters = 1 << (s->cluster_bits - REFCOUNT_SHIFT); + uint64_t blocks_used = (s->free_cluster_index + + refcount_block_clusters - 1) / refcount_block_clusters; + + /* And now we need at least one block more for the new metadata */ + uint64_t table_size = next_refcount_table_size(s, blocks_used + 1); + uint64_t last_table_size; + uint64_t blocks_clusters; + do { + uint64_t table_clusters = size_to_clusters(s, table_size); + blocks_clusters = 1 + + ((table_clusters + refcount_block_clusters - 1) + / refcount_block_clusters); + uint64_t meta_clusters = table_clusters + blocks_clusters; + + last_table_size = table_size; + table_size = next_refcount_table_size(s, blocks_used + + ((meta_clusters + refcount_block_clusters - 1) + / refcount_block_clusters)); + + } while (last_table_size != table_size); + +#ifdef DEBUG_ALLOC2 + fprintf(stderr, "qcow2: Grow refcount table %" PRId32 " => %" PRId64 "\n", + s->refcount_table_size, table_size); +#endif + + /* Create the new refcount table and blocks */ + uint64_t meta_offset = (blocks_used * refcount_block_clusters) * + s->cluster_size; + uint64_t table_offset = meta_offset + blocks_clusters * s->cluster_size; + uint16_t *new_blocks = qemu_mallocz(blocks_clusters * s->cluster_size); + uint64_t *new_table = qemu_mallocz(table_size * sizeof(uint64_t)); + + assert(meta_offset >= (s->free_cluster_index * s->cluster_size)); + + /* Fill the new refcount table */ memcpy(new_table, s->refcount_table, - s->refcount_table_size * sizeof(uint64_t)); - for(i = 0; i < s->refcount_table_size; i++) + s->refcount_table_size * sizeof(uint64_t)); + new_table[refcount_table_index] = new_block; + + int i; + for (i = 0; i < blocks_clusters; i++) { + new_table[blocks_used + i] = meta_offset + (i * s->cluster_size); + } + + /* Fill the refcount blocks */ + uint64_t table_clusters = size_to_clusters(s, table_size * sizeof(uint64_t)); + int block = 0; + for (i = 0; i < table_clusters + blocks_clusters; i++) { + new_blocks[block++] = cpu_to_be16(1); + } + + /* Write refcount blocks to disk */ + ret = bdrv_pwrite(s->hd, meta_offset, new_blocks, + blocks_clusters * s->cluster_size); + qemu_free(new_blocks); + if (ret < 0) { + goto fail_table; + } + + /* Write refcount table to disk */ + for(i = 0; i < table_size; i++) { cpu_to_be64s(&new_table[i]); - /* Note: we cannot update the refcount now to avoid recursion */ - table_offset = alloc_clusters_noref(bs, new_table_size2); - ret = bdrv_pwrite(s->hd, table_offset, new_table, new_table_size2); - if (ret != new_table_size2) - goto fail; - for(i = 0; i < s->refcount_table_size; i++) - be64_to_cpus(&new_table[i]); + } + + ret = bdrv_pwrite(s->hd, table_offset, new_table, + table_size * sizeof(uint64_t)); + if (ret < 0) { + goto fail_table; + } + for(i = 0; i < table_size; i++) { + cpu_to_be64s(&new_table[i]); + } + + /* Hook up the new refcount table in the qcow2 header */ + uint8_t data[12]; cpu_to_be64w((uint64_t*)data, table_offset); - cpu_to_be32w((uint32_t*)(data + 8), refcount_table_clusters); + cpu_to_be32w((uint32_t*)(data + 8), table_clusters); ret = bdrv_pwrite(s->hd, offsetof(QCowHeader, refcount_table_offset), - data, sizeof(data)); - if (ret != sizeof(data)) { - goto fail; + data, sizeof(data)); + if (ret < 0) { + goto fail_table; } + /* And switch it in memory */ + uint64_t old_table_offset = s->refcount_table_offset; + uint64_t old_table_size = s->refcount_table_size; + qemu_free(s->refcount_table); - old_table_offset = s->refcount_table_offset; - old_table_size = s->refcount_table_size; s->refcount_table = new_table; - s->refcount_table_size = new_table_size; + s->refcount_table_size = table_size; s->refcount_table_offset = table_offset; - update_refcount(bs, table_offset, new_table_size2, 1); + /* Free old table. Remember, we must not change free_cluster_index */ + uint64_t old_free_cluster_index = s->free_cluster_index; qcow2_free_clusters(bs, old_table_offset, old_table_size * sizeof(uint64_t)); - return 0; - fail: - qemu_free(new_table); - return ret < 0 ? ret : -EIO; -} - - -static int64_t alloc_refcount_block(BlockDriverState *bs, int64_t cluster_index) -{ - BDRVQcowState *s = bs->opaque; - int64_t offset, refcount_block_offset; - unsigned int refcount_table_index; - int ret; - uint64_t data64; - int cache = cache_refcount_updates; + s->free_cluster_index = old_free_cluster_index; - /* Find L1 index and grow refcount table if needed */ - refcount_table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT); - if (refcount_table_index >= s->refcount_table_size) { - ret = grow_refcount_table(bs, refcount_table_index + 1); - if (ret < 0) - return ret; + ret = load_refcount_block(bs, new_block); + if (ret < 0) { + goto fail_block; } - /* Load or allocate the refcount block */ - refcount_block_offset = s->refcount_table[refcount_table_index]; - if (!refcount_block_offset) { - if (cache_refcount_updates) { - write_refcount_block(s); - cache_refcount_updates = 0; - } - /* create a new refcount block */ - /* Note: we cannot update the refcount now to avoid recursion */ - offset = alloc_clusters_noref(bs, s->cluster_size); - memset(s->refcount_block_cache, 0, s->cluster_size); - ret = bdrv_pwrite(s->hd, offset, s->refcount_block_cache, s->cluster_size); - if (ret != s->cluster_size) - return -EINVAL; - s->refcount_table[refcount_table_index] = offset; - data64 = cpu_to_be64(offset); - ret = bdrv_pwrite(s->hd, s->refcount_table_offset + - refcount_table_index * sizeof(uint64_t), - &data64, sizeof(data64)); - if (ret != sizeof(data64)) - return -EINVAL; - - refcount_block_offset = offset; - s->refcount_block_cache_offset = offset; - update_refcount(bs, offset, s->cluster_size, 1); - cache_refcount_updates = cache; - } else { - if (refcount_block_offset != s->refcount_block_cache_offset) { - if (load_refcount_block(bs, refcount_block_offset) < 0) - return -EIO; - } - } + return new_block; - return refcount_block_offset; +fail_table: + qemu_free(new_table); +fail_block: + s->refcount_block_cache_offset = 0; + return ret; } #define REFCOUNTS_PER_SECTOR (512 >> REFCOUNT_SHIFT) |