block: Fix bdrv_is_allocated() for short backing files

bdrv_is_allocated() shouldn't return true for sectors that are
unallocated, but after the end of a short backing file, even though
such sectors are (correctly) marked as containing zeros.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

block.c

diff --git a/block.c b/block.c
index c90c71a..65e8191 100644
--- a/block.c
+++ b/block.c
@@ -3864,7 +3864,7 @@
 
     if (!bs->drv->bdrv_co_get_block_status) {
         *pnum = nb_sectors;
-        ret = BDRV_BLOCK_DATA;
+        ret = BDRV_BLOCK_DATA | BDRV_BLOCK_ALLOCATED;
         if (bs->drv->protocol_name) {
             ret |= BDRV_BLOCK_OFFSET_VALID | (sector_num * BDRV_SECTOR_SIZE);
         }
@@ -3883,6 +3883,10 @@
                                      *pnum, pnum);
     }
 
+    if (ret & (BDRV_BLOCK_DATA | BDRV_BLOCK_ZERO)) {
+        ret |= BDRV_BLOCK_ALLOCATED;
+    }
+
     if (!(ret & BDRV_BLOCK_DATA) && !(ret & BDRV_BLOCK_ZERO)) {
         if (bdrv_unallocated_blocks_are_zero(bs)) {
             ret |= BDRV_BLOCK_ZERO;
@@ -3959,9 +3963,7 @@
     if (ret < 0) {
         return ret;
     }
-    return
-        (ret & BDRV_BLOCK_DATA) ||
-        ((ret & BDRV_BLOCK_ZERO) && !bdrv_has_zero_init(bs));
+    return (ret & BDRV_BLOCK_ALLOCATED);
 }
 
 /*

include/block/block.h

diff --git a/include/block/block.h b/include/block/block.h
index 1b119aa..59be83f 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -120,6 +120,8 @@
 /* BDRV_BLOCK_DATA: data is read from bs->file or another file
  * BDRV_BLOCK_ZERO: sectors read as zero
  * BDRV_BLOCK_OFFSET_VALID: sector stored in bs->file as raw data
+ * BDRV_BLOCK_ALLOCATED: the content of the block is determined by this
+ *                       layer (as opposed to the backing file)
  * BDRV_BLOCK_RAW: used internally to indicate that the request
  *                 was answered by the raw driver and that one
  *                 should look in bs->file directly.
@@ -141,10 +143,11 @@
  *  f    t        f       not allocated or unknown offset, read as zero
  *  f    f        f       not allocated or unknown offset, read from backing_hd
  */
-#define BDRV_BLOCK_DATA         1
-#define BDRV_BLOCK_ZERO         2
-#define BDRV_BLOCK_OFFSET_VALID 4
-#define BDRV_BLOCK_RAW          8
+#define BDRV_BLOCK_DATA         0x01
+#define BDRV_BLOCK_ZERO         0x02
+#define BDRV_BLOCK_OFFSET_VALID 0x04
+#define BDRV_BLOCK_RAW          0x08
+#define BDRV_BLOCK_ALLOCATED    0x10
 #define BDRV_BLOCK_OFFSET_MASK  BDRV_SECTOR_MASK
 
 typedef enum {