[PATCH RFC v2 0/4] blockdev-replace

[PATCH RFC v2 0/4] blockdev-replace

[Vladimir Sementsov-Ogievskiy]

Hi all!

v2:

1. Let's start with minimal functionality: replace only one specific
child.

2. Explicit type of parent: qdev / export / driver

Hmm, 'driver' is for BlockDriverState.. Any better idea? I don't want to
call it "node" or even "block-node", as finally, devices and exports are
kind of nodes too in the whole block graph..

3. I think it's better to start with x- prefix

Plans for v3:

- add tests of filter insertion and removing
- add qmp transaction support

Vladimir Sementsov-Ogievskiy (4):
  block-backend: blk_root(): drop const specifier on return type
  block/export: add blk_by_export_id()
  block: make bdrv_find_child() function public
  qapi: add blockdev-replace command

 qapi/block.json                | 61 ++++++++++++++++++++++++++++++++++
 include/block/block_int.h      |  1 +
 include/sysemu/block-backend.h |  3 +-
 block.c                        | 13 ++++++++
 block/block-backend.c          |  2 +-
 block/export/export.c          | 18 ++++++++++
 block/qapi-sysemu.c            | 56 +++++++++++++++++++++++++++++++
 blockdev.c                     | 14 --------
 8 files changed, 152 insertions(+), 16 deletions(-)

-- 
2.31.1

[PATCH v2 1/4] block-backend: blk_root(): drop const specifier on return type

[Vladimir Sementsov-Ogievskiy]

We'll need get non-const child pointer for graph modifications in
further commits.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 include/sysemu/block-backend.h | 2 +-
 block/block-backend.c          | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index e5e1524f06..904d70f49c 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -277,7 +277,7 @@ int coroutine_fn blk_co_copy_range(BlockBackend *blk_in, int64_t off_in,
                                    int64_t bytes, BdrvRequestFlags read_flags,
                                    BdrvRequestFlags write_flags);
 
-const BdrvChild *blk_root(BlockBackend *blk);
+BdrvChild *blk_root(BlockBackend *blk);
 
 int blk_make_empty(BlockBackend *blk, Error **errp);
 
diff --git a/block/block-backend.c b/block/block-backend.c
index 12ef80ea17..d994a0f096 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -2438,7 +2438,7 @@ int coroutine_fn blk_co_copy_range(BlockBackend *blk_in, int64_t off_in,
                               bytes, read_flags, write_flags);
 }
 
-const BdrvChild *blk_root(BlockBackend *blk)
+BdrvChild *blk_root(BlockBackend *blk)
 {
     return blk->root;
 }
-- 
2.31.1

[PATCH v2 2/4] block/export: add blk_by_export_id()

[Vladimir Sementsov-Ogievskiy]

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 include/sysemu/block-backend.h |  1 +
 block/export/export.c          | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
index 904d70f49c..250c7465a5 100644
--- a/include/sysemu/block-backend.h
+++ b/include/sysemu/block-backend.h
@@ -124,6 +124,7 @@ DeviceState *blk_get_attached_dev(BlockBackend *blk);
 char *blk_get_attached_dev_id(BlockBackend *blk);
 BlockBackend *blk_by_dev(void *dev);
 BlockBackend *blk_by_qdev_id(const char *id, Error **errp);
+BlockBackend *blk_by_export_id(const char *id, Error **errp);
 void blk_set_dev_ops(BlockBackend *blk, const BlockDevOps *ops, void *opaque);
 int coroutine_fn blk_co_preadv(BlockBackend *blk, int64_t offset,
                                int64_t bytes, QEMUIOVector *qiov,
diff --git a/block/export/export.c b/block/export/export.c
index 6d3b9964c8..613b5bc1d5 100644
--- a/block/export/export.c
+++ b/block/export/export.c
@@ -362,3 +362,21 @@ BlockExportInfoList *qmp_query_block_exports(Error **errp)
 
     return head;
 }
+
+BlockBackend *blk_by_export_id(const char *id, Error **errp)
+{
+    BlockExport *exp;
+
+    exp = blk_exp_find(id);
+    if (exp == NULL) {
+        error_setg(errp, "Export '%s' not found", id);
+        return NULL;
+    }
+
+    if (!exp->blk) {
+        error_setg(errp, "Export '%s' is empty", id);
+        return NULL;
+    }
+
+    return exp->blk;
+}
-- 
2.31.1

[PATCH v2 3/4] block: make bdrv_find_child() function public

[Vladimir Sementsov-Ogievskiy]

To be reused soon.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 include/block/block_int.h |  1 +
 block.c                   | 13 +++++++++++++
 blockdev.c                | 14 --------------
 3 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/include/block/block_int.h b/include/block/block_int.h
index f4c75e8ba9..79bdde8bf4 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -1433,6 +1433,7 @@ BdrvDirtyBitmap *block_dirty_bitmap_remove(const char *node, const char *name,
                                            BlockDriverState **bitmap_bs,
                                            Error **errp);
 
+BdrvChild *bdrv_find_child(BlockDriverState *parent_bs, const char *child_name);
 BdrvChild *bdrv_cow_child(BlockDriverState *bs);
 BdrvChild *bdrv_filter_child(BlockDriverState *bs);
 BdrvChild *bdrv_filter_or_cow_child(BlockDriverState *bs);
diff --git a/block.c b/block.c
index 0ac5b163d2..840d52e7c8 100644
--- a/block.c
+++ b/block.c
@@ -7727,6 +7727,19 @@ int bdrv_make_empty(BdrvChild *c, Error **errp)
     return 0;
 }
 
+BdrvChild *bdrv_find_child(BlockDriverState *parent_bs, const char *child_name)
+{
+    BdrvChild *child;
+
+    QLIST_FOREACH(child, &parent_bs->children, next) {
+        if (strcmp(child->name, child_name) == 0) {
+            return child;
+        }
+    }
+
+    return NULL;
+}
+
 /*
  * Return the child that @bs acts as an overlay for, and from which data may be
  * copied in COW or COR operations.  Usually this is the backing file.
diff --git a/blockdev.c b/blockdev.c
index 0eb2823b1b..ce23059d5e 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3644,20 +3644,6 @@ out:
     aio_context_release(aio_context);
 }
 
-static BdrvChild *bdrv_find_child(BlockDriverState *parent_bs,
-                                  const char *child_name)
-{
-    BdrvChild *child;
-
-    QLIST_FOREACH(child, &parent_bs->children, next) {
-        if (strcmp(child->name, child_name) == 0) {
-            return child;
-        }
-    }
-
-    return NULL;
-}
-
 void qmp_x_blockdev_change(const char *parent, bool has_child,
                            const char *child, bool has_node,
                            const char *node, Error **errp)
-- 
2.31.1

[PATCH v2 4/4] qapi: add blockdev-replace command

[Vladimir Sementsov-Ogievskiy]

Add a command that can replace bs in following BdrvChild structures:

 - qdev blk root child
 - block-export blk root child
 - any child BlockDriverState selected by child-name

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 qapi/block.json     | 61 +++++++++++++++++++++++++++++++++++++++++++++
 block/qapi-sysemu.c | 56 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 117 insertions(+)

diff --git a/qapi/block.json b/qapi/block.json
index 82fcf2c914..a4dd1e34d4 100644
--- a/qapi/block.json
+++ b/qapi/block.json
@@ -570,3 +570,64 @@
            '*boundaries-read': ['uint64'],
            '*boundaries-write': ['uint64'],
            '*boundaries-flush': ['uint64'] } }
+##
+# @BlockParentType:
+#
+# Since 7.0
+##
+{ 'enum': 'BlockParentType',
+  'data': ['qdev', 'driver', 'export'] }
+
+##
+# @BdrvChildRefQdev:
+#
+# Since 7.0
+##
+{ 'struct': 'BdrvChildRefQdev',
+  'data': { 'qdev-id': 'str' } }
+
+##
+# @BdrvChildRefExport:
+#
+# Since 7.0
+##
+{ 'struct': 'BdrvChildRefExport',
+  'data': { 'export-id': 'str' } }
+
+##
+# @BdrvChildRefDriver:
+#
+# Since 7.0
+##
+{ 'struct': 'BdrvChildRefDriver',
+  'data': { 'node-name': 'str', 'child': 'str' } }
+
+##
+# @BlockdevReplace:
+#
+# Since 7.0
+##
+{ 'union': 'BlockdevReplace',
+  'base': {
+      'parent-type': 'BlockParentType',
+      'new-child': 'str'
+  },
+  'discriminator': 'parent-type',
+  'data': {
+      'qdev': 'BdrvChildRefQdev',
+      'export': 'BdrvChildRefExport',
+      'driver': 'BdrvChildRefDriver'
+  } }
+
+##
+# @x-blockdev-replace:
+#
+# Replace a block-node associated with device (selected by
+# @qdev-id) or with block-export (selected by @export-id) or
+# any child of block-node (selected by @node-name and @child)
+# with @new-child block-node.
+#
+# Since 7.0
+##
+{ 'command': 'x-blockdev-replace', 'boxed': true,
+  'data': 'BlockdevReplace' }
diff --git a/block/qapi-sysemu.c b/block/qapi-sysemu.c
index 8498402ad4..ca1aaef376 100644
--- a/block/qapi-sysemu.c
+++ b/block/qapi-sysemu.c
@@ -588,3 +588,59 @@ void qmp_block_latency_histogram_set(
         }
     }
 }
+
+void qmp_x_blockdev_replace(BlockdevReplace *repl, Error **errp)
+{
+    BdrvChild *child = NULL;
+    BlockDriverState *new_child_bs;
+
+    if (repl->parent_type == BLOCK_PARENT_TYPE_DRIVER) {
+        BlockDriverState *parent_bs;
+
+        parent_bs = bdrv_find_node(repl->u.driver.node_name);
+        if (!parent_bs) {
+            error_setg(errp, "Block driver node with node-name '%s' not "
+                       "found", repl->u.driver.node_name);
+            return;
+        }
+
+        child = bdrv_find_child(parent_bs, repl->u.driver.child);
+        if (!child) {
+            error_setg(errp, "Block driver node '%s' doesn't have child "
+                       "named '%s'", repl->u.driver.node_name,
+                       repl->u.driver.child);
+            return;
+        }
+    } else {
+        /* Other types are similar, they work through blk */
+        BlockBackend *blk;
+        bool is_qdev = repl->parent_type == BLOCK_PARENT_TYPE_QDEV;
+        const char *id =
+            is_qdev ? repl->u.qdev.qdev_id : repl->u.export.export_id;
+
+        assert(is_qdev || repl->parent_type == BLOCK_PARENT_TYPE_EXPORT);
+
+        blk = is_qdev ? blk_by_qdev_id(id, errp) : blk_by_export_id(id, errp);
+        if (!blk) {
+            return;
+        }
+
+        child = blk_root(blk);
+        if (!child) {
+            error_setg(errp, "%s '%s' is empty, nothing to replace",
+                       is_qdev ? "Device" : "Export", id);
+            return;
+        }
+    }
+
+    assert(child);
+    assert(child->bs);
+
+    new_child_bs = bdrv_find_node(repl->new_child);
+    if (!new_child_bs) {
+        error_setg(errp, "Node '%s' not found", repl->new_child);
+        return;
+    }
+
+    bdrv_replace_child_bs(child, new_child_bs, errp);
+}
-- 
2.31.1