block/qapi: Use blk_enable_write_cache()

Now that WCE is handled on the BlockBackend level, the flag is
meaningless for BDSes. As the schema requires us to fill the field,
we return an enabled write cache for them.

Note that this means that querying the BlockBackend name may return
writethrough as the cache information, whereas querying the node-name of
the root of that same BlockBackend will return writeback.

This may appear odd at first, but it actually makes sense because it
correctly repesents the layer that implements the WCE handling. This
becomes more apparent when you consider nodes that are the root node of
multiple BlockBackends, where each BB can have its own WCE setting.

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

block.c

@@ -2917,7 +2917,7 @@ BlockDeviceInfoList *bdrv_named_nodes_list(Error **errp)
 
     list = NULL;
     QTAILQ_FOREACH(bs, &graph_bdrv_states, node_list) {
-        BlockDeviceInfo *info = bdrv_block_device_info(bs, errp);
+        BlockDeviceInfo *info = bdrv_block_device_info(NULL, bs, errp);
         if (!info) {
             qapi_free_BlockDeviceInfoList(list);
             return NULL;

block/qapi.c

@@ -34,7 +34,8 @@
 #include "sysemu/block-backend.h"
 #include "qemu/cutils.h"
 
-BlockDeviceInfo *bdrv_block_device_info(BlockDriverState *bs, Error **errp)
+BlockDeviceInfo *bdrv_block_device_info(BlockBackend *blk,
+                                        BlockDriverState *bs, Error **errp)
 {
     ImageInfo **p_image_info;
     BlockDriverState *bs0;
@@ -48,7 +49,7 @@ BlockDeviceInfo *bdrv_block_device_info(BlockDriverState *bs, Error **errp)
 
     info->cache = g_new(BlockdevCacheInfo, 1);
     *info->cache = (BlockdevCacheInfo) {
-        .writeback      = bdrv_enable_write_cache(bs),
+        .writeback      = blk ? blk_enable_write_cache(blk) : true,
         .direct         = !!(bs->open_flags & BDRV_O_NOCACHE),
         .no_flush       = !!(bs->open_flags & BDRV_O_NO_FLUSH),
     };
@@ -343,7 +344,7 @@ static void bdrv_query_info(BlockBackend *blk, BlockInfo **p_info,
 
     if (bs && bs->drv) {
         info->has_inserted = true;
-        info->inserted = bdrv_block_device_info(bs, errp);
+        info->inserted = bdrv_block_device_info(blk, bs, errp);
         if (info->inserted == NULL) {
             goto err;
         }

include/block/qapi.h

@@ -29,7 +29,8 @@
 #include "block/block.h"
 #include "block/snapshot.h"
 
-BlockDeviceInfo *bdrv_block_device_info(BlockDriverState *bs, Error **errp);
+BlockDeviceInfo *bdrv_block_device_info(BlockBackend *blk,
+                                        BlockDriverState *bs, Error **errp);
 int bdrv_query_snapshot_info_list(BlockDriverState *bs,
                                   SnapshotInfoList **p_list,
                                   Error **errp);

tests/qemu-iotests/142

@@ -134,7 +134,8 @@ echo
 
 # First check the inherited cache mode after opening the image.
 
-hmp_cmds="info block image
+hmp_cmds="info block none0
+info block image
 info block file
 info block backing
 info block backing-file"
@@ -164,6 +165,7 @@ echo
 # new cache mode is specified in the flags, not as an option.
 
 hmp_cmds='qemu-io none0 "reopen -c none"
+info block none0
 info block image
 info block file
 info block backing
@@ -179,6 +181,7 @@ echo
 # new cache mode is specified as an option, not in the flags.
 
 hmp_cmds='qemu-io none0 "reopen -o cache.direct=on"
+info block none0
 info block image
 info block file
 info block backing
@@ -214,6 +217,7 @@ echo
 # options from its parent node.
 
 hmp_cmds="qemu-io none0 \"reopen -o cache.writeback=off,cache.direct=on,cache.no-flush=on\"
+info block none0
 info block image
 info block blkdebug
 info block file"
@@ -321,6 +325,7 @@ echo "--- Basic reopen ---"
 echo
 
 hmp_cmds='qemu-io none0 "reopen -o backing.cache.direct=on"
+info block none0
 info block image
 info block file
 info block backing

tests/qemu-iotests/142.out

@@ -39,14 +39,17 @@ cache.direct=on on none0
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
+    Cache mode:       writeback, direct
 
 cache.direct=on on file
+    Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback, direct
     Cache mode:       writeback
     Cache mode:       writeback
 
 cache.direct=on on backing
+    Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback, direct
@@ -56,6 +59,7 @@ cache.direct=on on backing-file
     Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback
+    Cache mode:       writeback
     Cache mode:       writeback, direct
 
 
@@ -64,6 +68,7 @@ cache.writeback=off on none0
     Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback
+    Cache mode:       writeback
 
 cache.writeback=off on file
 QEMU_PROG: -drive if=none,file=TEST_DIR/t.qcow2,backing.file.filename=TEST_DIR/t.qcow2.base,node-name=image,backing.node-name=backing,backing.file.node-name=backing-file,file.node-name=file,file.cache.writeback=off: Can't set writethrough mode except for the root
@@ -80,14 +85,17 @@ cache.no-flush=on on none0
     Cache mode:       writeback, ignore flushes
     Cache mode:       writeback, ignore flushes
     Cache mode:       writeback, ignore flushes
+    Cache mode:       writeback, ignore flushes
 
 cache.no-flush=on on file
+    Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback, ignore flushes
     Cache mode:       writeback
     Cache mode:       writeback
 
 cache.no-flush=on on backing
+    Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback, ignore flushes
@@ -97,6 +105,7 @@ cache.no-flush=on on backing-file
     Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback
+    Cache mode:       writeback
     Cache mode:       writeback, ignore flushes
 
 --- Cache modes after reopen (live snapshot) ---
@@ -182,24 +191,28 @@ cache.direct=on on none0
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
+    Cache mode:       writeback, direct
 
 cache.direct=on on file
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
+    Cache mode:       writeback, direct
 
 cache.direct=on on backing
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
+    Cache mode:       writeback, direct
 
 cache.direct=on on backing-file
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
+    Cache mode:       writeback, direct
 
 
 cache.writeback=off on none0
@@ -207,6 +220,7 @@ cache.writeback=off on none0
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
+    Cache mode:       writeback, direct
 
 cache.writeback=off on file
 QEMU_PROG: -drive if=none,file=TEST_DIR/t.qcow2,backing.file.filename=TEST_DIR/t.qcow2.base,node-name=image,backing.node-name=backing,backing.file.node-name=backing-file,file.node-name=file,file.cache.writeback=off: Can't set writethrough mode except for the root
@@ -223,14 +237,17 @@ cache.no-flush=on on none0
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
+    Cache mode:       writeback, direct
 
 cache.no-flush=on on file
+    Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct, ignore flushes
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
 
 cache.no-flush=on on backing
+    Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct, ignore flushes
@@ -240,6 +257,7 @@ cache.no-flush=on on backing-file
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
+    Cache mode:       writeback, direct
     Cache mode:       writeback, direct, ignore flushes
 
 --- Change cache modes with reopen (qemu-io command, options) ---
@@ -249,24 +267,28 @@ cache.direct=on on none0
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
+    Cache mode:       writeback, direct
 
 cache.direct=on on file
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
+    Cache mode:       writeback, direct
 
 cache.direct=on on backing
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
+    Cache mode:       writeback, direct
 
 cache.direct=on on backing-file
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
+    Cache mode:       writeback, direct
 
 
 cache.writeback=off on none0
@@ -274,6 +296,7 @@ cache.writeback=off on none0
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
+    Cache mode:       writeback, direct
 
 cache.writeback=off on file
 QEMU_PROG: -drive if=none,file=TEST_DIR/t.qcow2,backing.file.filename=TEST_DIR/t.qcow2.base,node-name=image,backing.node-name=backing,backing.file.node-name=backing-file,file.node-name=file,file.cache.writeback=off: Can't set writethrough mode except for the root
@@ -290,14 +313,17 @@ cache.no-flush=on on none0
     Cache mode:       writeback, direct, ignore flushes
     Cache mode:       writeback, direct, ignore flushes
     Cache mode:       writeback, direct, ignore flushes
+    Cache mode:       writeback, direct, ignore flushes
 
 cache.no-flush=on on file
+    Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct, ignore flushes
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
 
 cache.no-flush=on on backing
+    Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct, ignore flushes
@@ -307,6 +333,7 @@ cache.no-flush=on on backing-file
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
+    Cache mode:       writeback, direct
     Cache mode:       writeback, direct, ignore flushes
 
 --- Change cache modes after snapshot ---
@@ -389,6 +416,7 @@ cache.no-flush=on on backing-file
 
     Cache mode:       writethrough, direct, ignore flushes
     Cache mode:       writeback, direct, ignore flushes
+    Cache mode:       writeback, direct, ignore flushes
     Cache mode:       writeback, ignore flushes
 
 === Check that referenced BDSes don't inherit ===
@@ -422,28 +450,28 @@ cache.direct=on on backing-file
 
 
 cache.writeback=off on blk
-    Cache mode:       writethrough
+    Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback
 
 cache.writeback=off on file
     Cache mode:       writeback
-    Cache mode:       writethrough
+    Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback
 
 cache.writeback=off on backing
     Cache mode:       writeback
     Cache mode:       writeback
-    Cache mode:       writethrough
+    Cache mode:       writeback
     Cache mode:       writeback
 
 cache.writeback=off on backing-file
     Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback
-    Cache mode:       writethrough
+    Cache mode:       writeback
 
 
 cache.no-flush=on on blk
@@ -511,7 +539,7 @@ cache.writeback=off on blk
 cache.writeback=off on file
     Cache mode:       writeback
     Cache mode:       writeback
-    Cache mode:       writethrough
+    Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback
 
@@ -519,7 +547,7 @@ cache.writeback=off on backing
     Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback
-    Cache mode:       writethrough
+    Cache mode:       writeback
     Cache mode:       writeback
 
 cache.writeback=off on backing-file
@@ -527,7 +555,7 @@ cache.writeback=off on backing-file
     Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback
-    Cache mode:       writethrough
+    Cache mode:       writeback
 
 
 cache.no-flush=on on blk
@@ -593,21 +621,21 @@ cache.writeback=off on blk
 
 cache.writeback=off on file
     Cache mode:       writeback, direct
-    Cache mode:       writethrough
+    Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback
 
 cache.writeback=off on backing
     Cache mode:       writeback, direct
     Cache mode:       writeback
-    Cache mode:       writethrough
+    Cache mode:       writeback
     Cache mode:       writeback
 
 cache.writeback=off on backing-file
     Cache mode:       writeback, direct
     Cache mode:       writeback
     Cache mode:       writeback
-    Cache mode:       writethrough
+    Cache mode:       writeback
 
 
 cache.no-flush=on on blk
@@ -644,20 +672,24 @@ cache.direct=on on none0
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
+    Cache mode:       writeback, direct
 
 cache.direct=on on file
+    Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
 
 cache.direct=on on backing
+    Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
 
 cache.direct=on on backing-file
+    Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback, direct
@@ -667,6 +699,7 @@ cache.direct=on on backing-file
 cache.writeback=off on none0
     Cache mode:       writethrough
     Cache mode:       writeback
+    Cache mode:       writeback
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
 
@@ -681,24 +714,28 @@ QEMU_PROG: -drive if=none,file=TEST_DIR/t.qcow2,backing.file.filename=TEST_DIR/t
 
 
 cache.no-flush=on on none0
+    Cache mode:       writeback, ignore flushes
     Cache mode:       writeback, ignore flushes
     Cache mode:       writeback, ignore flushes
     Cache mode:       writeback, direct, ignore flushes
     Cache mode:       writeback, direct, ignore flushes
 
 cache.no-flush=on on file
+    Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback, ignore flushes
     Cache mode:       writeback, direct
     Cache mode:       writeback, direct
 
 cache.no-flush=on on backing
+    Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback, direct, ignore flushes
     Cache mode:       writeback, direct, ignore flushes
 
 cache.no-flush=on on backing-file
+    Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback
     Cache mode:       writeback, direct