[Qemu-devel] [PATCH v7 5/8] vmdk: Set maximum bytes allocated in one cycle

[Ashijeet Acharya <ashijeetacharya@gmail.com>]

Set the maximum bytes allowed to get allocated at once to be not more
than the extent size boundary to handle writes at two separate extents
appropriately.

Signed-off-by: Ashijeet Acharya <ashijeetacharya@gmail.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
---
 block/vmdk.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/block/vmdk.c b/block/vmdk.c
index 5647f53..fe2046b 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -1624,6 +1624,7 @@ static int vmdk_pwritev(BlockDriverState *bs, uint64_t offset,
     uint64_t cluster_offset;
     uint64_t bytes_done = 0;
     VmdkMetaData m_data;
+    uint64_t extent_end;
 
     if (DIV_ROUND_UP(offset, BDRV_SECTOR_SIZE) > bs->total_sectors) {
         error_report("Wrong offset: offset=0x%" PRIx64
@@ -1637,9 +1638,17 @@ static int vmdk_pwritev(BlockDriverState *bs, uint64_t offset,
         if (!extent) {
             return -EIO;
         }
+        extent_end = extent->end_sector * BDRV_SECTOR_SIZE;
+
         offset_in_cluster = vmdk_find_offset_in_cluster(extent, offset);
-        n_bytes = MIN(bytes, extent->cluster_sectors * BDRV_SECTOR_SIZE
-                             - offset_in_cluster);
+
+        /* truncate n_bytes to first cluster because we need to perform COW */
+        if (offset_in_cluster > 0) {
+            n_bytes = MIN(bytes, extent->cluster_sectors * BDRV_SECTOR_SIZE
+                                 - offset_in_cluster);
+        } else {
+            n_bytes = MIN(bytes, extent_end - offset);
+        }
 
         ret = vmdk_get_cluster_offset(bs, extent, &m_data, offset,
                                       !(extent->compressed || zeroed),
-- 
2.6.2