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[Qemu-devel] [PATCH 2/2] qcow2: truncate the tail of the image file afte
From: |
Pavel Butsykin |
Subject: |
[Qemu-devel] [PATCH 2/2] qcow2: truncate the tail of the image file after shrinking the image |
Date: |
Wed, 20 Sep 2017 16:58:33 +0300 |
Now after shrinking the image, at the end of the image file, there might be a
tail that probably will never be used. So we can find the last used cluster and
cut the tail.
Signed-off-by: Pavel Butsykin <address@hidden>
---
block/qcow2-refcount.c | 21 +++++++++++++++++++++
block/qcow2.c | 19 +++++++++++++++++++
block/qcow2.h | 1 +
3 files changed, 41 insertions(+)
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 88d5a3f1ad..5e221a166c 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -3181,3 +3181,24 @@ out:
g_free(reftable_tmp);
return ret;
}
+
+int64_t qcow2_get_last_cluster(BlockDriverState *bs, int64_t size)
+{
+ BDRVQcow2State *s = bs->opaque;
+ int64_t i, last_cluster, nb_clusters = size_to_clusters(s, size);
+ uint64_t refcount;
+
+ for (i = 0, last_cluster = 0; i < nb_clusters; i++) {
+ int ret = qcow2_get_refcount(bs, i, &refcount);
+ if (ret < 0) {
+ fprintf(stderr, "Can't get refcount for cluster %" PRId64 ": %s\n",
+ i, strerror(-ret));
+ continue;
+ }
+
+ if (refcount > 0) {
+ last_cluster = i;
+ }
+ }
+ return last_cluster;
+}
diff --git a/block/qcow2.c b/block/qcow2.c
index 8a4311d338..c3b6dd44c4 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -3106,6 +3106,7 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t
offset,
new_l1_size = size_to_l1(s, offset);
if (offset < old_length) {
+ int64_t image_end_offset, old_file_size;
if (prealloc != PREALLOC_MODE_OFF) {
error_setg(errp,
"Preallocation can't be used for shrinking an image");
@@ -3134,6 +3135,24 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t
offset,
"Failed to discard unused refblocks");
return ret;
}
+
+ old_file_size = bdrv_getlength(bs->file->bs);
+ if (old_file_size < 0) {
+ error_setg_errno(errp, -old_file_size,
+ "Failed to inquire current file length");
+ return old_file_size;
+ }
+ image_end_offset = (qcow2_get_last_cluster(bs, old_file_size) + 1) *
+ s->cluster_size;
+ if (image_end_offset < old_file_size) {
+ ret = bdrv_truncate(bs->file, image_end_offset,
+ PREALLOC_MODE_OFF, NULL);
+ if (ret < 0) {
+ error_setg_errno(errp, -ret,
+ "Failed to truncate the tail of the image");
+ return ret;
+ }
+ }
} else {
ret = qcow2_grow_l1_table(bs, new_l1_size, true);
if (ret < 0) {
diff --git a/block/qcow2.h b/block/qcow2.h
index 5a289a81e2..782a206ecb 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -597,6 +597,7 @@ int qcow2_change_refcount_order(BlockDriverState *bs, int
refcount_order,
BlockDriverAmendStatusCB *status_cb,
void *cb_opaque, Error **errp);
int qcow2_shrink_reftable(BlockDriverState *bs);
+int64_t qcow2_get_last_cluster(BlockDriverState *bs, int64_t size);
/* qcow2-cluster.c functions */
int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
--
2.14.1