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[Qemu-devel] [PATCH 2/5] qcow2: record fragmentation statistics during c


From: Stefan Hajnoczi
Subject: [Qemu-devel] [PATCH 2/5] qcow2: record fragmentation statistics during check
Date: Tue, 5 Feb 2013 19:54:08 +0100

The qemu-img check command can display fragmentation statistics:
 * Total number of clusters in virtual disk
 * Number of allocated clusters
 * Number of fragmented clusters

This patch adds fragmentation statistics support to qcow2.

Compressed and normal clusters count as allocated.  Zero clusters are
not counted as allocated unless their L2 entry has a non-zero offset
(e.g. preallocation).

Only the current L1 table counts towards the statistics - snapshots are
ignored.

Signed-off-by: Stefan Hajnoczi <address@hidden>
---
 block/qcow2-refcount.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index e2509ab..3d85e99 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -917,6 +917,7 @@ static void inc_refcounts(BlockDriverState *bs,
 /* Flags for check_refcounts_l1() and check_refcounts_l2() */
 enum {
     CHECK_OFLAG_COPIED = 0x1,   /* check QCOW_OFLAG_COPIED matches refcount */
+    CHECK_FRAG_INFO = 0x2,      /* update BlockFragInfo counters */
 };
 
 /*
@@ -933,6 +934,7 @@ static int check_refcounts_l2(BlockDriverState *bs, 
BdrvCheckResult *res,
 {
     BDRVQcowState *s = bs->opaque;
     uint64_t *l2_table, l2_entry;
+    uint64_t next_contiguous_offset = 0;
     int i, l2_size, nb_csectors, refcount;
 
     /* Read L2 table from disk */
@@ -963,6 +965,17 @@ static int check_refcounts_l2(BlockDriverState *bs, 
BdrvCheckResult *res,
             l2_entry &= s->cluster_offset_mask;
             inc_refcounts(bs, res, refcount_table, refcount_table_size,
                 l2_entry & ~511, nb_csectors * 512);
+
+            if (flags & CHECK_FRAG_INFO) {
+                res->bfi.allocated_clusters++;
+                if (next_contiguous_offset &&
+                    (l2_entry & ~511) != next_contiguous_offset) {
+                    res->bfi.fragmented_clusters++;
+                }
+                /* Round down again, see nb_sectors above */
+                next_contiguous_offset = (l2_entry & ~511) +
+                                         (nb_csectors - 1) * 512;
+            }
             break;
 
         case QCOW2_CLUSTER_ZERO:
@@ -990,6 +1003,15 @@ static int check_refcounts_l2(BlockDriverState *bs, 
BdrvCheckResult *res,
                 }
             }
 
+            if (flags & CHECK_FRAG_INFO) {
+                res->bfi.allocated_clusters++;
+                if (next_contiguous_offset &&
+                    offset != next_contiguous_offset) {
+                    res->bfi.fragmented_clusters++;
+                }
+                next_contiguous_offset = offset + s->cluster_size;
+            }
+
             /* Mark cluster as used */
             inc_refcounts(bs, res, refcount_table,refcount_table_size,
                 offset, s->cluster_size);
@@ -1125,6 +1147,7 @@ int qcow2_check_refcounts(BlockDriverState *bs, 
BdrvCheckResult *res,
 
     size = bdrv_getlength(bs->file);
     nb_clusters = size_to_clusters(s, size);
+    res->bfi.total_clusters = nb_clusters;
     refcount_table = g_malloc0(nb_clusters * sizeof(uint16_t));
 
     /* header */
@@ -1134,7 +1157,7 @@ int qcow2_check_refcounts(BlockDriverState *bs, 
BdrvCheckResult *res,
     /* current L1 table */
     ret = check_refcounts_l1(bs, res, refcount_table, nb_clusters,
                        s->l1_table_offset, s->l1_size,
-                       CHECK_OFLAG_COPIED);
+                       CHECK_OFLAG_COPIED | CHECK_FRAG_INFO);
     if (ret < 0) {
         goto fail;
     }
-- 
1.8.1




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