block: include base when checking image chain for block allocation

This patch is used in the 'block/stream: introduce a bottom node'
that is following. Instead of the base node, the caller may pass
the node that has the base as its backing image to the function
bdrv_is_allocated_above() with a new parameter include_base = true
and get rid of the dependency on the base that may change during
commit/stream parallel jobs. Now, if the specified base is not
found in the backing image chain, the QEMU will abort.

Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 1559152576-281803-2-git-send-email-andrey.shinkevich@virtuozzo.com
[mreitz: Squashed in the following as a rebase on conflicting patches:]
Message-id: e3cf99ae-62e9-8b6e-5a06-d3c8b9363b85@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

8 files changed, 24 insertions, 13 deletions

diff --git a/block/commit.c b/block/commit.c
index 212c6f639e..ca7e408b26 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -174,7 +174,7 @@ static int coroutine_fn commit_run(Job *job, Error **errp)
             break;
         }
         /* Copy if allocated above the base */
-        ret = bdrv_is_allocated_above(blk_bs(s->top), blk_bs(s->base),
+        ret = bdrv_is_allocated_above(blk_bs(s->top), blk_bs(s->base), false,
                                       offset, COMMIT_BUFFER_SIZE, &n);
         copy = (ret == 1);
         trace_commit_one_iteration(s, offset, n, ret);
diff --git a/block/io.c b/block/io.c
index 9ba1bada36..24a18759fd 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2295,10 +2295,11 @@ int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t offset,
 /*
  * Given an image chain: ... -> [BASE] -> [INTER1] -> [INTER2] -> [TOP]
  *
- * Return true if (a prefix of) the given range is allocated in any image
- * between BASE and TOP (inclusive).  BASE can be NULL to check if the given
- * offset is allocated in any image of the chain.  Return false otherwise,
- * or negative errno on failure.
+ * Return 1 if (a prefix of) the given range is allocated in any image
+ * between BASE and TOP (BASE is only included if include_base is set).
+ * BASE can be NULL to check if the given offset is allocated in any
+ * image of the chain.  Return 0 otherwise, or negative errno on
+ * failure.
  *
  * 'pnum' is set to the number of bytes (including and immediately
  * following the specified offset) that are known to be in the same
@@ -2310,17 +2311,21 @@ int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t offset,
  */
 int bdrv_is_allocated_above(BlockDriverState *top,
                             BlockDriverState *base,
-                            int64_t offset, int64_t bytes, int64_t *pnum)
+                            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 (intermediate && intermediate != base) {
+    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;
@@ -2339,6 +2344,10 @@ int bdrv_is_allocated_above(BlockDriverState *top,
             n = pnum_inter;
         }
 
+        if (intermediate == base) {
+            break;
+        }
+
         intermediate = backing_bs(intermediate);
     }
 
diff --git a/block/mirror.c b/block/mirror.c
index d17be4cdbc..2fcec70e35 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -808,7 +808,7 @@ static int coroutine_fn mirror_dirty_init(MirrorBlockJob *s)
             return 0;
         }
 
-        ret = bdrv_is_allocated_above(bs, base, offset, bytes, &count);
+        ret = bdrv_is_allocated_above(bs, base, false, offset, bytes, &count);
         if (ret < 0) {
             return ret;
         }
diff --git a/block/qcow2.c b/block/qcow2.c
index 9396d490d5..2a59eb27fe 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2148,7 +2148,8 @@ static bool is_unallocated(BlockDriverState *bs, int64_t offset, int64_t bytes)
 {
     int64_t nr;
     return !bytes ||
-        (!bdrv_is_allocated_above(bs, NULL, offset, bytes, &nr) && nr == bytes);
+        (!bdrv_is_allocated_above(bs, NULL, false, offset, bytes, &nr) &&
+         nr == bytes);
 }
 
 static bool is_zero_cow(BlockDriverState *bs, QCowL2Meta *m)
diff --git a/block/replication.c b/block/replication.c
index b41bc507c0..23b2993d74 100644
--- a/block/replication.c
+++ b/block/replication.c
@@ -275,7 +275,7 @@ static coroutine_fn int replication_co_writev(BlockDriverState *bs,
     while (remaining_sectors > 0) {
         int64_t count;
 
-        ret = bdrv_is_allocated_above(top->bs, base->bs,
+        ret = bdrv_is_allocated_above(top->bs, base->bs, false,
                                       sector_num * BDRV_SECTOR_SIZE,
                                       remaining_sectors * BDRV_SECTOR_SIZE,
                                       &count);
diff --git a/block/stream.c b/block/stream.c
index 1a906fd860..97fddb2608 100644
--- a/block/stream.c
+++ b/block/stream.c
@@ -160,7 +160,7 @@ static int coroutine_fn stream_run(Job *job, Error **errp)
         } else if (ret >= 0) {
             /* Copy if allocated in the intermediate images.  Limit to the
              * known-unallocated area [offset, offset+n*BDRV_SECTOR_SIZE).  */
-            ret = bdrv_is_allocated_above(backing_bs(bs), base,
+            ret = bdrv_is_allocated_above(backing_bs(bs), base, false,
                                           offset, n, &n);
 
             /* Finish early if end of backing file has been reached */
diff --git a/include/block/block.h b/include/block/block.h
index f9415ed740..734c9d2f76 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -449,7 +449,8 @@ int bdrv_block_status_above(BlockDriverState *bs, BlockDriverState *base,
 int bdrv_is_allocated(BlockDriverState *bs, int64_t offset, int64_t bytes,
                       int64_t *pnum);
 int bdrv_is_allocated_above(BlockDriverState *top, BlockDriverState *base,
-                            int64_t offset, int64_t bytes, int64_t *pnum);
+                            bool include_base, int64_t offset, int64_t bytes,
+                            int64_t *pnum);
 
 bool bdrv_is_read_only(BlockDriverState *bs);
 int bdrv_can_set_read_only(BlockDriverState *bs, bool read_only,
diff --git a/qemu-img.c b/qemu-img.c
index 158b3a505f..79983772de 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -3518,7 +3518,7 @@ static int img_rebase(int argc, char **argv)
                  * to take action
                  */
                 ret = bdrv_is_allocated_above(backing_bs(bs), prefix_chain_bs,
-                                              offset, n, &n);
+                                              false, offset, n, &n);
                 if (ret < 0) {
                     error_report("error while reading image metadata: %s",
                                  strerror(-ret));