[Qemu-devel] [PATCH 2/5] block: Add a mechanism for passing a block driver a block configuration

[Ari Sundholm]

A block driver may need to know about the block configuration, most
critically the sector sizes, of a block backend for alignment purposes
or for some other reason. It doesn't seem like qemu has an existing
mechanism for a block backend to convey the required information to
the relevant block driver when it is being realized.

The need for this mechanism rises from the fact that a drive may not
have a backend at the time it is created, as devices are created after
drives during qemu startup. Therefore, a driver requiring information
about the block configuration can get this information when a backend
is created for it at the earliest. The most natural place for this to
take place seems to be in the realization functions of the various
block device drivers, such as scsi-hd. The interface proposed here
allows the block driver to receive information about the block
configuration and the associated backend through a new callback.

Signed-off-by: Ari Sundholm <address@hidden>
---
 block/io.c                | 19 +++++++++++++++++++
 hw/block/block.c          | 11 ++++++++++-
 include/block/block.h     | 10 ++++++++++
 include/block/block_int.h |  9 +++++++++
 include/hw/block/block.h  |  1 +
 5 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/block/io.c b/block/io.c
index ca96b48..b806c91 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2835,3 +2835,22 @@ void bdrv_unregister_buf(BlockDriverState *bs, void 
*host)
         bdrv_unregister_buf(child->bs, host);
     }
 }
+
+void bdrv_apply_blkconf(BlockDriverState *bs, BlockConf *conf)
+{
+    BlockDriver *drv = bs->drv;
+
+    if (!drv)
+        return;
+
+    if (drv->bdrv_apply_blkconf) {
+        drv->bdrv_apply_blkconf(bs, conf);
+        return;
+    }
+
+    if (bs->file && bs->file->bs)
+        bdrv_apply_blkconf(bs->file->bs, conf);
+
+    if (bs->drv->supports_backing && backing_bs(bs))
+        bdrv_apply_blkconf(backing_bs(bs), conf);
+}
diff --git a/hw/block/block.c b/hw/block/block.c
index b91e2b6..a2d33df 100644
--- a/hw/block/block.c
+++ b/hw/block/block.c
@@ -38,7 +38,7 @@ void blkconf_blocksizes(BlockConf *conf)
     /* fill in detected values if they are not defined via qemu command line */
     if (!conf->physical_block_size) {
         if (!backend_ret) {
-           conf->physical_block_size = blocksizes.phys;
+            conf->physical_block_size = blocksizes.phys;
         } else {
             conf->physical_block_size = BDRV_SECTOR_SIZE;
         }
@@ -52,6 +52,15 @@ void blkconf_blocksizes(BlockConf *conf)
     }
 }
 
+void blkconf_apply_to_blkdrv(BlockConf *conf)
+{
+    BlockBackend *blk = conf->blk;
+    BlockDriverState *bs = blk_bs(blk);
+
+    if (bs)
+        bdrv_apply_blkconf(bs, conf);
+}
+
 bool blkconf_apply_backend_options(BlockConf *conf, bool readonly,
                                    bool resizable, Error **errp)
 {
diff --git a/include/block/block.h b/include/block/block.h
index fb7d379..57a8b65 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -10,6 +10,7 @@
 #include "block/dirty-bitmap.h"
 #include "block/blockjob.h"
 #include "qemu/hbitmap.h"
+#include "hw/block/block.h"
 
 /* block.c */
 typedef struct BlockDriver BlockDriver;
@@ -618,4 +619,13 @@ bool bdrv_can_store_new_dirty_bitmap(BlockDriverState *bs, 
const char *name,
  */
 void bdrv_register_buf(BlockDriverState *bs, void *host, size_t size);
 void bdrv_unregister_buf(BlockDriverState *bs, void *host);
+
+/**
+ * bdrv_apply_blkconf:
+ *
+ * Recursively finds the highest-level block drivers among the files and
+ * backing files that accept a block configuration and applies the given block
+ * configuration to them.
+ */
+void bdrv_apply_blkconf(BlockDriverState *bs, BlockConf *conf);
 #endif
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 6c0927b..1d99a0d 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -433,6 +433,15 @@ struct BlockDriver {
     void (*bdrv_abort_perm_update)(BlockDriverState *bs);
 
     /**
+     * Called to inform the driver of the block configuration of the virtual
+     * block device.
+     *
+     * This function is called by a block device realization function if the
+     * device wants to inform the block driver of its block configuration.
+     */
+    void (*bdrv_apply_blkconf)(BlockDriverState *bs, BlockConf *conf);
+
+    /**
      * Returns in @nperm and @nshared the permissions that the driver for @bs
      * needs on its child @c, based on the cumulative permissions requested by
      * the parents in @parent_perm and @parent_shared.
diff --git a/include/hw/block/block.h b/include/hw/block/block.h
index d4f4dff..2861995 100644
--- a/include/hw/block/block.h
+++ b/include/hw/block/block.h
@@ -77,6 +77,7 @@ bool blkconf_geometry(BlockConf *conf, int *trans,
                       unsigned cyls_max, unsigned heads_max, unsigned secs_max,
                       Error **errp);
 void blkconf_blocksizes(BlockConf *conf);
+void blkconf_apply_to_blkdrv(BlockConf *conf);
 bool blkconf_apply_backend_options(BlockConf *conf, bool readonly,
                                    bool resizable, Error **errp);
 
-- 
2.7.4