[Qemu-devel] [PATCH] qemu-img: find the highest offset in use during check

[Federico Simoncelli]

This patch adds the support for reporting the highest offset in use by
an image. This is particularly useful after a conversion (or a rebase)
where the destination is a block device in order to find the actual
amount of space in use.

Signed-off-by: Federico Simoncelli <address@hidden>
---
 block.h                |    1 +
 block/qcow2-refcount.c |   10 ++++++++--
 qemu-img.c             |    4 ++++
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/block.h b/block.h
index 722c620..de42e8c 100644
--- a/block.h
+++ b/block.h
@@ -213,6 +213,7 @@ typedef struct BdrvCheckResult {
     int check_errors;
     int corruptions_fixed;
     int leaks_fixed;
+    int64_t highest_offset;
     BlockFragInfo bfi;
 } BdrvCheckResult;
 
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 96224d1..017439d 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -1116,7 +1116,7 @@ int qcow2_check_refcounts(BlockDriverState *bs, 
BdrvCheckResult *res,
                           BdrvCheckMode fix)
 {
     BDRVQcowState *s = bs->opaque;
-    int64_t size, i;
+    int64_t size, i, highest_cluster;
     int nb_clusters, refcount1, refcount2;
     QCowSnapshot *sn;
     uint16_t *refcount_table;
@@ -1154,7 +1154,7 @@ int qcow2_check_refcounts(BlockDriverState *bs, 
BdrvCheckResult *res,
         s->refcount_table_offset,
         s->refcount_table_size * sizeof(uint64_t));
 
-    for(i = 0; i < s->refcount_table_size; i++) {
+    for(i = 0, highest_cluster = 0; i < s->refcount_table_size; i++) {
         uint64_t offset, cluster;
         offset = s->refcount_table[i];
         cluster = offset >> s->cluster_bits;
@@ -1197,6 +1197,11 @@ int qcow2_check_refcounts(BlockDriverState *bs, 
BdrvCheckResult *res,
         }
 
         refcount2 = refcount_table[i];
+
+        if (refcount1 > 0 || refcount2 > 0) {
+            highest_cluster = i;
+        }
+
         if (refcount1 != refcount2) {
 
             /* Check if we're allowed to fix the mismatch */
@@ -1231,6 +1236,7 @@ int qcow2_check_refcounts(BlockDriverState *bs, 
BdrvCheckResult *res,
         }
     }
 
+    res->highest_offset = (highest_cluster + 1) * s->cluster_size;
     ret = 0;
 
 fail:
diff --git a/qemu-img.c b/qemu-img.c
index e29e01b..3a8090b 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -470,6 +470,10 @@ static int img_check(int argc, char **argv)
         result.bfi.fragmented_clusters * 100.0 / 
result.bfi.allocated_clusters);
     }
 
+    if (result.highest_offset > 0) {
+        printf("Highest offset in use: %lu\n", result.highest_offset);
+    }
+
     bdrv_delete(bs);
 
     if (ret < 0 || result.check_errors) {
-- 
1.7.1