[PULL 17/29] parallels: Remove unnecessary data_end field

["Denis V. Lunev" <den@openvz.org>]

From: Denis V. Lunev <den@openvz.org>

Since we have used bitmap, field data_end in BDRVParallelsState is
redundant and can be removed.

Add parallels_data_end() helper and remove data_end handling.

The two are not equivalent, which is why this comes before the Format
Extension is stored. data_end is the highest extent seen in the BAT,
while the helper derives the end of the payload from the image file. A
cluster which belongs to the image without being referenced by the BAT,
as the Format Extension and its bitmap data clusters are, stays
invisible to the field: parallels_allocate_host_clusters() appends at
data_end, so it would hand out an offset which is already occupied and
parallels_mark_used() would refuse it with -EBUSY, failing the guest
write.

seek_to_sector() validates a BAT entry against data_end, so it becomes
a user of the new helper, which suits that check better as well: a
cluster has to live inside the image file, while the field could grow
to whatever extent a corrupted BAT entry claimed.

The BAT scan in parallels_open() no longer tracks the maximum extent,
but it keeps rejecting entries below data_start or beyond the end of the
file, so need_check is still set when an entry is out of bounds. Nothing
is accumulated any more, so the scan stops at the first such entry.
high_off in parallels_check_outside_image() only fed the
image_end_offset which the helper now provides, so it goes away with
the field.

The bdrv_pwrite_zeroes() of the branch which reuses a hole goes as well.
It was guarded by data_end, and it is redundant: the space was already
fallocated when the image grew over it. The 'bytes' variable goes with
it, as the used bitmap grows by the preallocated size rather than the
requested one.

Based on the original work from Alexander Ivanov.

Cc: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
---
 block/parallels.c | 57 +++++++++++++----------------------------------
 block/parallels.h |  1 -
 2 files changed, 15 insertions(+), 43 deletions(-)

diff --git a/block/parallels.c b/block/parallels.c
index 2be7c20338..ace79ad968 100644
--- a/block/parallels.c
+++ b/block/parallels.c
@@ -116,6 +116,13 @@ static uint32_t bat_entry_off(uint32_t idx)
     return sizeof(ParallelsHeader) + sizeof(uint32_t) * idx;
 }
 
+static int64_t parallels_data_end(BDRVParallelsState *s)
+{
+    int64_t data_end = s->data_start * BDRV_SECTOR_SIZE;
+    data_end += s->used_bmap_size * s->cluster_size;
+    return data_end;
+}
+
 static int64_t seek_to_sector(BDRVParallelsState *s, int64_t sector_num)
 {
     uint32_t index, offset;
@@ -130,7 +137,8 @@ static int64_t seek_to_sector(BDRVParallelsState *s, int64_t sector_num)
     }
 
     cluster_off = bat2sect(s, index);
-    if (cluster_off < s->data_start || cluster_off + s->tracks > s->data_end) {
+    if (cluster_off < s->data_start ||
+        cluster_off + s->tracks > parallels_data_end(s) >> BDRV_SECTOR_BITS) {
         /* Cluster is outside of the image file or overlaps the header. */
         return -1;
     }
@@ -284,15 +292,14 @@ int64_t GRAPH_RDLOCK parallels_allocate_host_clusters(BlockDriverState *bs,
 {
     BDRVParallelsState *s = bs->opaque;
     int64_t first_free, next_used, host_off, prealloc_clusters;
-    int64_t bytes, prealloc_bytes;
+    int64_t prealloc_bytes;
     uint32_t new_usedsize;
     int ret = 0;
 
     first_free = find_first_zero_bit(s->used_bmap, s->used_bmap_size);
     if (first_free == s->used_bmap_size) {
-        host_off = s->data_end * BDRV_SECTOR_SIZE;
+        host_off = parallels_data_end(s);
         prealloc_clusters = *clusters + s->prealloc_size / s->tracks;
-        bytes = *clusters * s->cluster_size;
         prealloc_bytes = prealloc_clusters * s->cluster_size;
 
         /*
@@ -323,27 +330,9 @@ int64_t GRAPH_RDLOCK parallels_allocate_host_clusters(BlockDriverState *bs,
 
         /* Not enough continuous clusters in the middle, adjust the size */
         *clusters = MIN(*clusters, next_used - first_free);
-        bytes = *clusters * s->cluster_size;
 
         host_off = s->data_start * BDRV_SECTOR_SIZE;
         host_off += first_free * s->cluster_size;
-
-        /*
-         * No need to preallocate if we are using tail area from the above
-         * branch. In the other case we are likely re-using hole. Preallocate
-         * the space if required by the prealloc_mode.
-         */
-        if (s->prealloc_mode == PRL_PREALLOC_MODE_FALLOCATE &&
-                host_off < s->data_end * BDRV_SECTOR_SIZE) {
-            ret = bdrv_pwrite_zeroes(bs->file, host_off, bytes, 0);
-            if (ret < 0) {
-                return ret;
-            }
-        }
-    }
-
-    if (host_off + bytes > s->data_end * BDRV_SECTOR_SIZE) {
-        s->data_end = (host_off + bytes) / BDRV_SECTOR_SIZE;
     }
 
     ret = parallels_mark_used(bs, s->used_bmap, s->used_bmap_size,
@@ -749,7 +738,7 @@ parallels_check_outside_image(BlockDriverState *bs, BdrvCheckResult *res,
 {
     BDRVParallelsState *s = bs->opaque;
     uint32_t i;
-    int64_t off, high_off, size, data_start_off;
+    int64_t off, size, data_start_off;
     bool fixed = false;
 
     size = bdrv_co_getlength(bs->file->bs);
@@ -759,7 +748,6 @@ parallels_check_outside_image(BlockDriverState *bs, BdrvCheckResult *res,
     }
     data_start_off = s->data_start << BDRV_SECTOR_BITS;
 
-    high_off = 0;
     for (i = 0; i < s->bat_size; i++) {
         off = bat2sect(s, i) << BDRV_SECTOR_BITS;
         if (off == 0) {
@@ -774,10 +762,6 @@ parallels_check_outside_image(BlockDriverState *bs, BdrvCheckResult *res,
                 res->corruptions_fixed++;
                 fixed = true;
             }
-            continue;
-        }
-        if (high_off < off) {
-            high_off = off;
         }
     }
 
@@ -792,14 +776,7 @@ parallels_check_outside_image(BlockDriverState *bs, BdrvCheckResult *res,
         }
     }
 
-    if (high_off == 0) {
-        res->image_end_offset = s->data_end << BDRV_SECTOR_BITS;
-    } else {
-        res->image_end_offset = high_off + s->cluster_size;
-        s->data_end = res->image_end_offset >> BDRV_SECTOR_BITS;
-    }
-
-
+    res->image_end_offset = parallels_data_end(s);
     return 0;
 }
 
@@ -1466,8 +1443,7 @@ static int parallels_open(BlockDriverState *bs, QDict *options, int flags,
     }
 
     s->data_start = data_start;
-    s->data_end = s->data_start;
-    if (s->data_end < (s->header_size >> BDRV_SECTOR_BITS)) {
+    if (s->data_start < (s->header_size >> BDRV_SECTOR_BITS)) {
         /*
          * There is not enough unused space to fit to block align between BAT
          * and actual data. We can't avoid read-modify-write...
@@ -1530,10 +1506,7 @@ static int parallels_open(BlockDriverState *bs, QDict *options, int flags,
         if (sector < data_start || sector + s->tracks > file_nb_sectors) {
             /* Cluster is outside of the image file or overlaps the header. */
             need_check = true;
-            continue;
-        }
-        if (sector + s->tracks > s->data_end) {
-            s->data_end = sector + s->tracks;
+            break;
         }
     }
 
diff --git a/block/parallels.h b/block/parallels.h
index 493c89e976..eb90aeea81 100644
--- a/block/parallels.h
+++ b/block/parallels.h
@@ -79,7 +79,6 @@ typedef struct BDRVParallelsState {
     unsigned int bat_size;
 
     int64_t  data_start;
-    int64_t  data_end;
     uint64_t prealloc_size;
     ParallelsPreallocMode prealloc_mode;
 
-- 
2.53.0