[Qemu-devel] [PATCH v6 1/9] block: add bdrv_measure() API

[Stefan Hajnoczi]

bdrv_measure() provides a conservative maximum for the size of a new
image.  This information is handy if storage needs to be allocated (e.g.
a SAN or an LVM volume) ahead of time.

Signed-off-by: Stefan Hajnoczi <address@hidden>
Reviewed-by: Alberto Garcia <address@hidden>
---
v6:
 * Change bdrv_measure() return type to BlockMeasureInfo * [Eric]
 * Clarify that holes in sparse POSIX files are still counted [Eric]
---
 qapi/block-core.json      | 25 +++++++++++++++++++++++++
 include/block/block.h     |  2 ++
 include/block/block_int.h |  2 ++
 block.c                   | 35 +++++++++++++++++++++++++++++++++++
 4 files changed, 64 insertions(+)

diff --git a/qapi/block-core.json b/qapi/block-core.json
index 87fb747..90795f7 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -463,6 +463,31 @@
            '*dirty-bitmaps': ['BlockDirtyInfo'] } }
 
 ##
+# @BlockMeasureInfo:
+#
+# Image file size calculation information.  This structure describes the size
+# requirements for creating a new image file.
+#
+# The size requirements depend on the new image file format.  File size always
+# equals virtual disk size for the 'raw' format, even for sparse POSIX files.
+# Compact formats such as 'qcow2' represent unallocated and zero regions
+# efficiently so file size may be smaller than virtual disk size.
+#
+# The values are upper bounds that are guaranteed to fit the new image file.
+# Subsequent modification, such as internal snapshot or bitmap creation, may
+# require additional space and is not covered here.
+#
+# @required: Size required for a new image file, in bytes.
+#
+# @fully-allocated: Image file size, in bytes, once data has been written
+#                   to all sectors.
+#
+# Since: 2.10
+##
+{ 'struct': 'BlockMeasureInfo',
+  'data': {'required': 'int', 'fully-allocated': 'int'} }
+
+##
 # @query-block:
 #
 # Get a list of BlockInfo for all virtual block devices.
diff --git a/include/block/block.h b/include/block/block.h
index 862eb56..4bfd7ae 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -298,6 +298,8 @@ int bdrv_truncate(BdrvChild *child, int64_t offset, Error 
**errp);
 int64_t bdrv_nb_sectors(BlockDriverState *bs);
 int64_t bdrv_getlength(BlockDriverState *bs);
 int64_t bdrv_get_allocated_file_size(BlockDriverState *bs);
+BlockMeasureInfo *bdrv_measure(BlockDriver *drv, QemuOpts *opts,
+                               BlockDriverState *in_bs, Error **errp);
 void bdrv_get_geometry(BlockDriverState *bs, uint64_t *nb_sectors_ptr);
 void bdrv_refresh_limits(BlockDriverState *bs, Error **errp);
 int bdrv_commit(BlockDriverState *bs);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 8773940..9788a69 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -201,6 +201,8 @@ struct BlockDriver {
     int64_t (*bdrv_getlength)(BlockDriverState *bs);
     bool has_variable_length;
     int64_t (*bdrv_get_allocated_file_size)(BlockDriverState *bs);
+    BlockMeasureInfo *(*bdrv_measure)(QemuOpts *opts, BlockDriverState *in_bs,
+                                      Error **errp);
 
     int coroutine_fn (*bdrv_co_pwritev_compressed)(BlockDriverState *bs,
         uint64_t offset, uint64_t bytes, QEMUIOVector *qiov);
diff --git a/block.c b/block.c
index 6c6bb3e..5bc6827 100644
--- a/block.c
+++ b/block.c
@@ -3359,6 +3359,41 @@ int64_t bdrv_get_allocated_file_size(BlockDriverState 
*bs)
     return -ENOTSUP;
 }
 
+/*
+ * bdrv_measure:
+ * @drv: Format driver
+ * @opts: Creation options for new image
+ * @in_bs: Existing image containing data for new image (may be NULL)
+ * @errp: Error object
+ * Returns: A #BlockMeasureInfo (free using qapi_free_BlockMeasureInfo())
+ *          or NULL on error
+ *
+ * Calculate file size required to create a new image.
+ *
+ * If @in_bs is given then space for allocated clusters and zero clusters
+ * from that image are included in the calculation.  If @opts contains a
+ * backing file that is shared by @in_bs then backing clusters are omitted
+ * from the calculation.
+ *
+ * If @in_bs is NULL then the calculation includes no allocated clusters
+ * unless a preallocation option is given in @opts.
+ *
+ * Note that @in_bs may use a different BlockDriver from @drv.
+ *
+ * If an error occurs the @errp pointer is set.
+ */
+BlockMeasureInfo *bdrv_measure(BlockDriver *drv, QemuOpts *opts,
+                               BlockDriverState *in_bs, Error **errp)
+{
+    if (!drv->bdrv_measure) {
+        error_setg(errp, "Block driver '%s' does not support size measurement",
+                   drv->format_name);
+        return NULL;
+    }
+
+    return drv->bdrv_measure(opts, in_bs, errp);
+}
+
 /**
  * Return number of sectors on success, -errno on error.
  */
-- 
2.9.3