Am 10.10.2014 um 14:32 schrieb Eric Blake:
On 08/26/2014 03:36 PM, Max Reitz wrote:
bdrv_make_empty() is currently only called if the current image
represents an external snapshot that has been committed to its base
image; it is therefore unlikely to have internal snapshots. In this
case, bdrv_make_empty() can be greatly sped up by emptying the L1 and
refcount table (while having the dirty flag set) and creating a trivial
refcount structure.
If there are snapshots, fall back to the simple implementation (discard
all clusters).
Signed-off-by: Max Reitz <[email protected]>
---
block/blkdebug.c | 2 +
block/qcow2.c | 137 ++++++++++++++++++++++++++++++++++++++++++++------
include/block/block.h | 2 +
3 files changed, 126 insertions(+), 15 deletions(-)
+ } else {
+ int l1_clusters;
+ int64_t offset;
+ uint64_t *new_reftable;
+ uint8_t l1_ofs_rt_ofs_cls[20]; /* L1 offset; RT offset and clusters */
+ uint64_t rt_entry;
+
+ ret = qcow2_cache_empty(bs, s->l2_table_cache);
if (ret < 0) {
- break;
+ return ret;
+ }
+
+ ret = qcow2_cache_empty(bs, s->refcount_block_cache);
+ if (ret < 0) {
+ return ret;
+ }
+
+ /* Refcounts will be broken utterly */
+ ret = qcow2_mark_dirty(bs);
qcow2_mark_dirty does assert(s->qcow_version >= 3). But this code can
be reached when committing a qcow2 0.10 compat-level file, right?
You're right, this code doesn't work for compat=0.10. As you proposed in
your own answer to this, I'll just use the fallback code in that case
(in v13)
+ /* "Create" an empty reftable (one cluster) directly after the image
+ * header and an empty L1 table three clusters after the image header;
+ * the cluster between those two will be used as the first refblock */
+ cpu_to_be64w((uint64_t *)&l1_ofs_rt_ofs_cls[ 0], 3 * s->cluster_size);
+ cpu_to_be64w((uint64_t *)&l1_ofs_rt_ofs_cls[ 8], s->cluster_size);
+ cpu_to_be32w((uint32_t *)&l1_ofs_rt_ofs_cls[16], 1);
The offsets here feel a bit magic.
Well, such byte offsets are everywhere in the qcow2 code which does such
small writes to the image header. Making them non-magic would mean
offsetof(...) - offsetof(...). Can and will do, but I probably won't
find it much more readable. ;-)
Max
