qcow2: Update multiple refcounts at once

Message-id: <1252527484-19604-3-git-send-email-ehabkost@redhat.com>
RH-Author: Eduardo Habkost <ehabkost@redhat.com>
Patchwork-id: 3386
O-Subject: [PATCH 2/5] qcow2: Update multiple refcounts at once
Bugzilla:

Author: Kevin Wolf <kwolf@redhat.com>
Bugzilla: 520693
RH-Acked-by: Juan Quintela <quintela@redhat.com>
RH-Acked-by: Andrea Arcangeli <aarcange@redhat.com>
RH-Acked-by: Gleb Natapov <gleb@redhat.com>

Don't write each single changed refcount block entry to the disk after it is
written, but update all entries of the block and write all of them at once.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
---
 qemu/block-qcow2.c |   40 ++++++++++++++++++++++++++++++++++++----
 1 files changed, 36 insertions(+), 4 deletions(-)

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 qemu/block-qcow2.c |   40 ++++++++++++++++++++++++++++++++++++----
 1 files changed, 36 insertions(+), 4 deletions(-)

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

1 files changed, 36 insertions, 4 deletions

diff --git a/qemu/block-qcow2.c b/qemu/block-qcow2.c
index 466de8ae..171eb83f 100644
--- a/qemu/block-qcow2.c
+++ b/qemu/block-qcow2.c
@@ -2588,6 +2588,9 @@ static int update_refcount(BlockDriverState *bs,
 {
     BDRVQcowState *s = bs->opaque;
     int64_t start, last, cluster_offset;
+    int64_t refcount_block_offset = 0;
+    int64_t table_index = -1, old_table_index;
+    int first_index = -1, last_index = -1;
 
 #ifdef DEBUG_ALLOC2
     printf("update_refcount: offset=%lld size=%lld addend=%d\n",
@@ -2600,10 +2603,25 @@ static int update_refcount(BlockDriverState *bs,
     for(cluster_offset = start; cluster_offset <= last;
         cluster_offset += s->cluster_size)
     {
-        int64_t refcount_block_offset;
         int block_index, refcount;
         int64_t cluster_index = cluster_offset >> s->cluster_bits;
 
+        /* Only write refcount block to disk when we are done with it */
+        old_table_index = table_index;
+        table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);
+        if ((old_table_index >= 0) && (table_index != old_table_index)) {
+            size_t size = (last_index - first_index + 1) << REFCOUNT_SHIFT;
+            if (bdrv_pwrite(s->hd,
+                refcount_block_offset + (first_index << REFCOUNT_SHIFT),
+                &s->refcount_block_cache[first_index], size) != size)
+            {
+                return -EIO;
+            }
+
+            first_index = -1;
+            last_index = -1;
+        }
+
         /* Load the refcount block and allocate it if needed */
         refcount_block_offset = alloc_refcount_block(bs, cluster_index);
         if (refcount_block_offset < 0) {
@@ -2613,6 +2631,13 @@ static int update_refcount(BlockDriverState *bs,
         /* we can update the count and save it */
         block_index = cluster_index &
             ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);
+        if (first_index == -1 || block_index < first_index) {
+            first_index = block_index;
+        }
+        if (block_index > last_index) {
+            last_index = block_index;
+        }
+
         refcount = be16_to_cpu(s->refcount_block_cache[block_index]);
         refcount += addend;
         if (refcount < 0 || refcount > 0xffff)
@@ -2621,12 +2646,19 @@ static int update_refcount(BlockDriverState *bs,
             s->free_cluster_index = cluster_index;
         }
         s->refcount_block_cache[block_index] = cpu_to_be16(refcount);
+    }
+
+    /* Write last changed block to disk */
+    if (refcount_block_offset != 0) {
+        size_t size = (last_index - first_index + 1) << REFCOUNT_SHIFT;
         if (bdrv_pwrite(s->hd,
-                        refcount_block_offset + (block_index << REFCOUNT_SHIFT),
-                        &s->refcount_block_cache[block_index], 2) != 2)
+            refcount_block_offset + (first_index << REFCOUNT_SHIFT),
+            &s->refcount_block_cache[first_index], size) != size)
+        {
             return -EIO;
-
+        }
     }
+
     return 0;
 }