@@ -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);
@@ -123,124 +123,265 @@ static int get_refcount(BlockDriverState *bs, int64_t cluster_index)
return be16_to_cpu(s->refcount_block_cache[block_index]);
}
-static int grow_refcount_table(BlockDriverState *bs, int min_size)
+/*
+ * Rounds the refcount table size up to avoid growing the table for each single
+ * refcount block that is allocated.
+ */
+static unsigned int next_refcount_table_size(BDRVQcowState *s,
+ unsigned int min_size)
{
- 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_clusters = 0;
+ unsigned int new_table_size = 1;
- if (min_size <= s->refcount_table_size)
- return 0;
- /* compute new table size */
- refcount_table_clusters = s->refcount_table_size >> (s->cluster_bits - 3);
- for(;;) {
+ while (min_size > new_table_size) {
if (refcount_table_clusters == 0) {
refcount_table_clusters = 1;
} else {
refcount_table_clusters = (refcount_table_clusters * 3 + 1) / 2;
}
new_table_size = refcount_table_clusters << (s->cluster_bits - 3);
- if (min_size <= new_table_size)
- break;
}
-#ifdef DEBUG_ALLOC2
- printf("grow_refcount_table from %d to %d\n",
- s->refcount_table_size,
- new_table_size);
-#endif
- new_table_size2 = new_table_size * sizeof(uint64_t);
- new_table = qemu_mallocz(new_table_size2);
- memcpy(new_table, s->refcount_table,
- s->refcount_table_size * sizeof(uint64_t));
- for(i = 0; i < s->refcount_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]);
- cpu_to_be64w((uint64_t*)data, table_offset);
- cpu_to_be32w((uint32_t*)(data + 8), refcount_table_clusters);
- ret = bdrv_pwrite(s->hd, offsetof(QCowHeader, refcount_table_offset),
- data, sizeof(data));
- if (ret != sizeof(data)) {
- goto fail;
- }
+ return new_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_offset = table_offset;
+/* 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);
- update_refcount(bs, table_offset, new_table_size2, 1);
- 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;
+ 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;
- int64_t offset, refcount_block_offset;
unsigned int refcount_table_index;
+ uint64_t refcount_block_offset;
int ret;
- uint64_t data64;
- int cache = cache_refcount_updates;
- /* Find L1 index and grow refcount table if needed */
+ /* 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) {
- ret = grow_refcount_table(bs, refcount_table_index + 1);
- if (ret < 0)
- return ret;
+ refcount_block_offset = 0;
+ } else {
+ refcount_block_offset = s->refcount_table[refcount_table_index];
}
- /* 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;
+ /* 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;
+ }
}
- /* 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;
+ 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) {
+ write_refcount_block(s);
+ }
+
+ /* 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;
+
+#ifdef DEBUG_ALLOC2
+ fprintf(stderr, "qcow2: Allocate refcount block %d for %" PRIx64
+ " at %" PRIx64 "\n",
+ refcount_table_index, cluster_index << s->cluster_bits, new_block);
+#endif
+
+ 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 {
- if (refcount_block_offset != s->refcount_block_cache_offset) {
- if (load_refcount_block(bs, refcount_block_offset) < 0)
- return -EIO;
+ /* 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;
}
- return refcount_block_offset;
+ /*
+ * 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 = 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;
+
+ 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));
+ 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]);
+ }
+
+ 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), table_clusters);
+ ret = bdrv_pwrite(s->hd, offsetof(QCowHeader, refcount_table_offset),
+ 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);
+ s->refcount_table = new_table;
+ s->refcount_table_size = table_size;
+ s->refcount_table_offset = table_offset;
+
+ /* 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));
+ s->free_cluster_index = old_free_cluster_index;
+
+ ret = load_refcount_block(bs, new_block);
+ if (ret < 0) {
+ goto fail_block;
+ }
+
+ return new_block;
+
+fail_table:
+ qemu_free(new_table);
+fail_block:
+ s->refcount_block_cache_offset = 0;
+ return ret;
}
#define REFCOUNTS_PER_SECTOR (512 >> REFCOUNT_SHIFT)
@@ -923,9 +1064,21 @@ int qcow2_check_refcounts(BlockDriverState *bs)
for(i = 0; i < s->refcount_table_size; i++) {
int64_t offset;
offset = s->refcount_table[i];
+
+ /* Refcount blocks are cluster aligned */
+ if (offset & (s->cluster_size - 1)) {
+ fprintf(stderr, "ERROR refcount block %d is not "
+ "cluster aligned; refcount table entry corrupted\n", i);
+ errors++;
+ }
+
if (offset != 0) {
errors += inc_refcounts(bs, refcount_table, nb_clusters,
offset, s->cluster_size);
+ if (refcount_table[offset / s->cluster_size] != 1) {
+ fprintf(stderr, "ERROR refcount block %d refcount=%d\n",
+ i, refcount_table[offset / s->cluster_size]);
+ }
}
}