1 files changed, 75 insertions, 57 deletions

diff --git a/block/io.c b/block/io.c
index 54f0968aee..02528b3823 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2343,6 +2343,7 @@ early_out:
 int coroutine_fn
 bdrv_co_common_block_status_above(BlockDriverState *bs,
                                   BlockDriverState *base,
+                                  bool include_base,
                                   bool want_zero,
                                   int64_t offset,
                                   int64_t bytes,
@@ -2350,34 +2351,84 @@ bdrv_co_common_block_status_above(BlockDriverState *bs,
                                   int64_t *map,
                                   BlockDriverState **file)
 {
+    int ret;
     BlockDriverState *p;
-    int ret = 0;
-    bool first = true;
+    int64_t eof = 0;
+
+    assert(!include_base || base); /* Can't include NULL base */
+
+    if (!include_base && bs == base) {
+        *pnum = bytes;
+        return 0;
+    }
+
+    ret = bdrv_co_block_status(bs, want_zero, offset, bytes, pnum, map, file);
+    if (ret < 0 || *pnum == 0 || ret & BDRV_BLOCK_ALLOCATED || bs == base) {
+        return ret;
+    }
+
+    if (ret & BDRV_BLOCK_EOF) {
+        eof = offset + *pnum;
+    }
+
+    assert(*pnum <= bytes);
+    bytes = *pnum;
 
-    assert(bs != base);
-    for (p = bs; p != base; p = bdrv_filter_or_cow_bs(p)) {
+    for (p = bdrv_filter_or_cow_bs(bs); include_base || p != base;
+         p = bdrv_filter_or_cow_bs(p))
+    {
         ret = bdrv_co_block_status(p, want_zero, offset, bytes, pnum, map,
                                    file);
         if (ret < 0) {
-            break;
+            return ret;
         }
-        if (ret & BDRV_BLOCK_ZERO && ret & BDRV_BLOCK_EOF && !first) {
+        if (*pnum == 0) {
             /*
-             * Reading beyond the end of the file continues to read
-             * zeroes, but we can only widen the result to the
-             * unallocated length we learned from an earlier
-             * iteration.
+             * The top layer deferred to this layer, and because this layer is
+             * short, any zeroes that we synthesize beyond EOF behave as if they
+             * were allocated at this layer.
+             *
+             * We don't include BDRV_BLOCK_EOF into ret, as upper layer may be
+             * larger. We'll add BDRV_BLOCK_EOF if needed at function end, see
+             * below.
              */
+            assert(ret & BDRV_BLOCK_EOF);
             *pnum = bytes;
+            if (file) {
+                *file = p;
+            }
+            ret = BDRV_BLOCK_ZERO | BDRV_BLOCK_ALLOCATED;
+            break;
+        }
+        if (ret & BDRV_BLOCK_ALLOCATED) {
+            /*
+             * We've found the node and the status, we must break.
+             *
+             * Drop BDRV_BLOCK_EOF, as it's not for upper layer, which may be
+             * larger. We'll add BDRV_BLOCK_EOF if needed at function end, see
+             * below.
+             */
+            ret &= ~BDRV_BLOCK_EOF;
+            break;
         }
-        if (ret & (BDRV_BLOCK_ZERO | BDRV_BLOCK_DATA)) {
+
+        if (p == base) {
+            assert(include_base);
             break;
         }
-        /* [offset, pnum] unallocated on this layer, which could be only
-         * the first part of [offset, bytes].  */
-        bytes = MIN(bytes, *pnum);
-        first = false;
+
+        /*
+         * OK, [offset, offset + *pnum) region is unallocated on this layer,
+         * let's continue the diving.
+         */
+        assert(*pnum <= bytes);
+        bytes = *pnum;
+    }
+
+    if (offset + *pnum == eof) {
+        ret |= BDRV_BLOCK_EOF;
     }
+
     return ret;
 }
 
@@ -2385,7 +2436,7 @@ int bdrv_block_status_above(BlockDriverState *bs, BlockDriverState *base,
                             int64_t offset, int64_t bytes, int64_t *pnum,
                             int64_t *map, BlockDriverState **file)
 {
-    return bdrv_common_block_status_above(bs, base, true, offset, bytes,
+    return bdrv_common_block_status_above(bs, base, false, true, offset, bytes,
                                           pnum, map, file);
 }
 
@@ -2402,9 +2453,9 @@ int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t offset,
     int ret;
     int64_t dummy;
 
-    ret = bdrv_common_block_status_above(bs, bdrv_filter_or_cow_bs(bs), false,
-                                         offset, bytes, pnum ? pnum : &dummy,
-                                         NULL, NULL);
+    ret = bdrv_common_block_status_above(bs, bs, true, false, offset,
+                                         bytes, pnum ? pnum : &dummy, NULL,
+                                         NULL);
     if (ret < 0) {
         return ret;
     }
@@ -2426,52 +2477,19 @@ int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t offset,
  * at 'offset + *pnum' may return the same allocation status (in other
  * words, the result is not necessarily the maximum possible range);
  * but 'pnum' will only be 0 when end of file is reached.
- *
  */
 int bdrv_is_allocated_above(BlockDriverState *top,
                             BlockDriverState *base,
                             bool include_base, int64_t offset,
                             int64_t bytes, int64_t *pnum)
 {
-    BlockDriverState *intermediate;
-    int ret;
-    int64_t n = bytes;
-
-    assert(base || !include_base);
-
-    intermediate = top;
-    while (include_base || intermediate != base) {
-        int64_t pnum_inter;
-        int64_t size_inter;
-
-        assert(intermediate);
-        ret = bdrv_is_allocated(intermediate, offset, bytes, &pnum_inter);
-        if (ret < 0) {
-            return ret;
-        }
-        if (ret) {
-            *pnum = pnum_inter;
-            return 1;
-        }
-
-        size_inter = bdrv_getlength(intermediate);
-        if (size_inter < 0) {
-            return size_inter;
-        }
-        if (n > pnum_inter &&
-            (intermediate == top || offset + pnum_inter < size_inter)) {
-            n = pnum_inter;
-        }
-
-        if (intermediate == base) {
-            break;
-        }
-
-        intermediate = bdrv_filter_or_cow_bs(intermediate);
+    int ret = bdrv_common_block_status_above(top, base, include_base, false,
+                                             offset, bytes, pnum, NULL, NULL);
+    if (ret < 0) {
+        return ret;
     }
 
-    *pnum = n;
-    return 0;
+    return !!(ret & BDRV_BLOCK_ALLOCATED);
 }
 
 int coroutine_fn