[Qemu-devel] [PATCH v2 4/7] vmdk: New functions to allocate multiple clusters and cluster offset

[Ashijeet Acharya <ashijeetacharya@gmail.com>]

Introduce two new helper functions handle_alloc() and
vmdk_alloc_cluster_offset(). handle_alloc() helps to allocate multiple
clusters at once starting from a given offset on disk and performs COW
if necessary for first and last allocated clusters.
vmdk_alloc_cluster_offset() helps to return the offset of the first of
the many newly allocated clusters. Also, provide proper documentation
for both.

Signed-off-by: Ashijeet Acharya <ashijeetacharya@gmail.com>
---
 block/vmdk.c | 206 +++++++++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 187 insertions(+), 19 deletions(-)

diff --git a/block/vmdk.c b/block/vmdk.c
index a42322e..5a95929 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -136,6 +136,7 @@ typedef struct VmdkMetaData {
     unsigned int l2_offset;
     int valid;
     uint32_t *l2_cache_entry;
+    uint32_t nb_clusters;
 } VmdkMetaData;
 
 typedef struct VmdkGrainMarker {
@@ -1036,6 +1037,34 @@ static void vmdk_refresh_limits(BlockDriverState *bs, Error **errp)
     }
 }
 
+static int vmdk_L2update(VmdkExtent *extent, VmdkMetaData *m_data,
+                         uint32_t offset)
+{
+    offset = cpu_to_le32(offset);
+    /* update L2 table */
+    if (bdrv_pwrite_sync(extent->file,
+                ((int64_t)m_data->l2_offset * 512)
+                    + (m_data->l2_index * sizeof(offset)),
+                &offset, sizeof(offset)) < 0) {
+        return VMDK_ERROR;
+    }
+    /* update backup L2 table */
+    if (extent->l1_backup_table_offset != 0) {
+        m_data->l2_offset = extent->l1_backup_table[m_data->l1_index];
+        if (bdrv_pwrite_sync(extent->file,
+                    ((int64_t)m_data->l2_offset * 512)
+                        + (m_data->l2_index * sizeof(offset)),
+                    &offset, sizeof(offset)) < 0) {
+            return VMDK_ERROR;
+        }
+    }
+    if (m_data->l2_cache_entry) {
+        *m_data->l2_cache_entry = offset;
+    }
+
+    return VMDK_OK;
+}
+
 /*
  * vmdk_L2load
  *
@@ -1222,29 +1251,168 @@ exit:
     return ret;
 }
 
-static int vmdk_L2update(VmdkExtent *extent, VmdkMetaData *m_data,
-                         uint32_t offset)
+/*
+ * handle_alloc
+ *
+ * Allocates new clusters for an area that either is yet unallocated or needs a
+ * copy on write. If *cluster_offset is non_zero, clusters are only allocated if
+ * the new allocation can match the specified host offset.
+ *
+ * Returns:
+ *   VMDK_OK:       if new clusters were allocated, *bytes may be decreased if
+ *                  the new allocation doesn't cover all of the requested area.
+ *                  *cluster_offset is updated to contain the offset of the
+ *                  first newly allocated cluster.
+ *
+ *   VMDK_UNALLOC:  if no clusters could be allocated. *cluster_offset is left
+ *                  unchanged.
+ *
+ *   VMDK_ERROR:    in error cases
+ */
+static int handle_alloc(BlockDriverState *bs, VmdkExtent *extent,
+                        uint64_t offset, uint64_t *cluster_offset,
+                        int64_t *bytes, VmdkMetaData *m_data,
+                        bool allocate, uint32_t *total_alloc_clusters)
 {
-    offset = cpu_to_le32(offset);
-    /* update L2 table */
-    if (bdrv_pwrite_sync(extent->file,
-                ((int64_t)m_data->l2_offset * 512)
-                    + (m_data->l2_index * sizeof(offset)),
-                &offset, sizeof(offset)) < 0) {
-        return VMDK_ERROR;
+    int l1_index, l2_offset, l2_index;
+    uint32_t *l2_table;
+    uint32_t cluster_sector;
+    uint32_t nb_clusters;
+    bool zeroed = false;
+    uint64_t skip_start_bytes, skip_end_bytes;
+    int ret;
+
+    ret = get_cluster_table(extent, offset, &l1_index, &l2_offset,
+                            &l2_index, &l2_table);
+    if (ret < 0) {
+        return ret;
     }
-    /* update backup L2 table */
-    if (extent->l1_backup_table_offset != 0) {
-        m_data->l2_offset = extent->l1_backup_table[m_data->l1_index];
-        if (bdrv_pwrite_sync(extent->file,
-                    ((int64_t)m_data->l2_offset * 512)
-                        + (m_data->l2_index * sizeof(offset)),
-                    &offset, sizeof(offset)) < 0) {
-            return VMDK_ERROR;
+
+    cluster_sector = le32_to_cpu(l2_table[l2_index]);
+
+    skip_start_bytes = vmdk_find_offset_in_cluster(extent, offset);
+    /* Calculate the number of clusters to look for. Here it will return one
+     * cluster less than the actual value calculated as we may need to perfrom
+     * COW for the last one. */
+    nb_clusters = size_to_clusters(extent, skip_start_bytes + *bytes);
+
+    nb_clusters = MIN(nb_clusters, extent->l2_size - l2_index);
+    assert(nb_clusters <= INT_MAX);
+
+    /* update bytes according to final nb_clusters value */
+    if (nb_clusters != 0) {
+        *bytes = ((nb_clusters * extent->cluster_sectors) << 9)
+                                            - skip_start_bytes;
+    } else {
+        nb_clusters = 1;
+    }
+    *total_alloc_clusters += nb_clusters;
+    skip_end_bytes = skip_start_bytes + MIN(*bytes,
+                     extent->cluster_sectors * BDRV_SECTOR_SIZE
+                                    - skip_start_bytes);
+
+    if (extent->has_zero_grain && cluster_sector == VMDK_GTE_ZEROED) {
+        zeroed = true;
+    }
+
+    if (!cluster_sector || zeroed) {
+        if (!allocate) {
+            return zeroed ? VMDK_ZEROED : VMDK_UNALLOC;
+        }
+
+        cluster_sector = extent->next_cluster_sector;
+        extent->next_cluster_sector += extent->cluster_sectors
+                                                * nb_clusters;
+
+        ret = vmdk_perform_cow(bs, extent, cluster_sector * BDRV_SECTOR_SIZE,
+                               offset, skip_start_bytes,
+                               skip_end_bytes);
+        if (ret < 0) {
+            return ret;
+        }
+        if (m_data) {
+            m_data->valid = 1;
+            m_data->l1_index = l1_index;
+            m_data->l2_index = l2_index;
+            m_data->l2_offset = l2_offset;
+            m_data->l2_cache_entry = &l2_table[l2_index];
+            m_data->nb_clusters = nb_clusters;
         }
     }
-    if (m_data->l2_cache_entry) {
-        *m_data->l2_cache_entry = offset;
+    *cluster_offset = cluster_sector << BDRV_SECTOR_BITS;
+    return VMDK_OK;
+}
+
+/*
+ * vmdk_alloc_cluster_offset
+ *
+ * For a given offset on the virtual disk, find the cluster offset in vmdk
+ * file. If the offset is not found, allocate a new cluster.
+ *
+ * If the cluster is newly allocated, m_data->nb_clusters is set to the number
+ * of contiguous clusters that have been allocated. In this case, the other
+ * fields of m_data are valid and contain information about the first allocated
+ * cluster.
+ *
+ * Returns:
+ *
+ *   VMDK_OK:           on success and @cluster_offset was set
+ *
+ *   VMDK_UNALLOC:      if no clusters were allocated and @cluster_offset is
+ *                      set to zero
+ *
+ *   VMDK_ERROR:        in error cases
+ */
+static int vmdk_alloc_cluster_offset(BlockDriverState *bs,
+                                     VmdkExtent *extent,
+                                     VmdkMetaData *m_data, uint64_t offset,
+                                     bool allocate, uint64_t *cluster_offset,
+                                     int64_t bytes,
+                                     uint32_t *total_alloc_clusters)
+{
+    uint64_t start, remaining;
+    uint64_t new_cluster_offset;
+    int64_t n_bytes;
+    int ret;
+
+    if (extent->flat) {
+        *cluster_offset = extent->flat_start_offset;
+        return VMDK_OK;
+    }
+
+    start = offset;
+    remaining = bytes;
+    new_cluster_offset = 0;
+    *cluster_offset = 0;
+    n_bytes = 0;
+    if (m_data) {
+        m_data->valid = 0;
+    }
+
+    /* due to L2 table margins all bytes may not get allocated at once */
+    while (true) {
+
+        if (!*cluster_offset) {
+            *cluster_offset = new_cluster_offset;
+        }
+
+        start              += n_bytes;
+        remaining          -= n_bytes;
+        new_cluster_offset += n_bytes;
+
+        if (remaining == 0) {
+            break;
+        }
+
+        n_bytes = remaining;
+
+        ret = handle_alloc(bs, extent, start, &new_cluster_offset, &n_bytes,
+                           m_data, allocate, total_alloc_clusters);
+
+        if (ret < 0) {
+            return ret;
+
+        }
     }
 
     return VMDK_OK;
-- 
2.6.2