[PATCH v2 0/2] block: bdrv_reopen() with backing file in different AioContext

[PATCH v2 0/2] block: bdrv_reopen() with backing file in different AioContext

[Kevin Wolf]

v2:
- Fix bdrv_reopen_can_attach() call [Berto]

Kevin Wolf (2):
  iotests: Refactor blockdev-reopen test for iothreads
  block: bdrv_reopen() with backing file in different AioContext

 block.c                    | 32 ++++++++++++++++++++++-----
 tests/qemu-iotests/245     | 45 +++++++++++++++++++++++++++++---------
 tests/qemu-iotests/245.out |  4 ++--
 3 files changed, 63 insertions(+), 18 deletions(-)

-- 
2.20.1

[PATCH v2 1/2] iotests: Refactor blockdev-reopen test for iothreads

[Kevin Wolf]

We'll want to test more than one successful case in the future, so
prepare the test for that by a refactoring that runs each scenario in a
separate VM.

test_iothreads_switch_{backing,overlay} currently produce errors, but
these are cases that should actually work, by switching either the
backing file node or the overlay node to the AioContext of the other
node.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Tested-by: Peter Krempa <pkrempa@redhat.com>
---
 tests/qemu-iotests/245     | 47 ++++++++++++++++++++++++++++++--------
 tests/qemu-iotests/245.out |  4 ++--
 2 files changed, 39 insertions(+), 12 deletions(-)

diff --git a/tests/qemu-iotests/245 b/tests/qemu-iotests/245
index 489bf78bd0..7d9eb6285c 100755
--- a/tests/qemu-iotests/245
+++ b/tests/qemu-iotests/245
@@ -970,8 +970,7 @@ class TestBlockdevReopen(iotests.QMPTestCase):
         self.assertEqual(self.get_node('hd1'), None)
         self.assert_qmp(self.get_node('hd2'), 'ro', True)
 
-    # We don't allow setting a backing file that uses a different AioContext
-    def test_iothreads(self):
+    def run_test_iothreads(self, iothread_a, iothread_b, errmsg = None):
         opts = hd_opts(0)
         result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
         self.assert_qmp(result, 'return', {})
@@ -986,20 +985,48 @@ class TestBlockdevReopen(iotests.QMPTestCase):
         result = self.vm.qmp('object-add', qom_type='iothread', id='iothread1')
         self.assert_qmp(result, 'return', {})
 
-        result = self.vm.qmp('x-blockdev-set-iothread', node_name='hd0', iothread='iothread0')
+        result = self.vm.qmp('device_add', driver='virtio-scsi', id='scsi0',
+                             iothread=iothread_a)
         self.assert_qmp(result, 'return', {})
 
-        self.reopen(opts, {'backing': 'hd2'}, "Cannot use a new backing file with a different AioContext")
-
-        result = self.vm.qmp('x-blockdev-set-iothread', node_name='hd2', iothread='iothread1')
+        result = self.vm.qmp('device_add', driver='virtio-scsi', id='scsi1',
+                             iothread=iothread_b)
         self.assert_qmp(result, 'return', {})
 
-        self.reopen(opts, {'backing': 'hd2'}, "Cannot use a new backing file with a different AioContext")
+        if iothread_a:
+            result = self.vm.qmp('device_add', driver='scsi-hd', drive='hd0',
+                                 share_rw=True, bus="scsi0.0")
+            self.assert_qmp(result, 'return', {})
 
-        result = self.vm.qmp('x-blockdev-set-iothread', node_name='hd2', iothread='iothread0')
-        self.assert_qmp(result, 'return', {})
+        if iothread_b:
+            result = self.vm.qmp('device_add', driver='scsi-hd', drive='hd2',
+                                 share_rw=True, bus="scsi1.0")
+            self.assert_qmp(result, 'return', {})
 
-        self.reopen(opts, {'backing': 'hd2'})
+        # Attaching the backing file may or may not work
+        self.reopen(opts, {'backing': 'hd2'}, errmsg)
+
+        # But removing the backing file should always work
+        self.reopen(opts, {'backing': None})
+
+        self.vm.shutdown()
+
+    # We don't allow setting a backing file that uses a different AioContext if
+    # neither of them can switch to the other AioContext
+    def test_iothreads_error(self):
+        self.run_test_iothreads('iothread0', 'iothread1',
+                                "Cannot use a new backing file with a different AioContext")
+
+    def test_iothreads_compatible_users(self):
+        self.run_test_iothreads('iothread0', 'iothread0')
+
+    def test_iothreads_switch_backing(self):
+        self.run_test_iothreads('iothread0', None,
+                                "Cannot use a new backing file with a different AioContext")
+
+    def test_iothreads_switch_overlay(self):
+        self.run_test_iothreads(None, 'iothread0',
+                                "Cannot use a new backing file with a different AioContext")
 
 if __name__ == '__main__':
     iotests.main(supported_fmts=["qcow2"],
diff --git a/tests/qemu-iotests/245.out b/tests/qemu-iotests/245.out
index a19de5214d..682b93394d 100644
--- a/tests/qemu-iotests/245.out
+++ b/tests/qemu-iotests/245.out
@@ -1,6 +1,6 @@
-..................
+.....................
 ----------------------------------------------------------------------
-Ran 18 tests
+Ran 21 tests
 
 OK
 {"execute": "job-finalize", "arguments": {"id": "commit0"}}
-- 
2.20.1

Re: [PATCH v2 1/2] iotests: Refactor blockdev-reopen test for iothreads

[John Snow]

On 3/6/20 9:14 AM, Kevin Wolf wrote:
> We'll want to test more than one successful case in the future, so
> prepare the test for that by a refactoring that runs each scenario in a
> separate VM.
> 
> test_iothreads_switch_{backing,overlay} currently produce errors, but
> these are cases that should actually work, by switching either the
> backing file node or the overlay node to the AioContext of the other
> node.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> Tested-by: Peter Krempa <pkrempa@redhat.com>

Reviewed-by: John Snow <jsnow@redhat.com>

> ---
>  tests/qemu-iotests/245     | 47 ++++++++++++++++++++++++++++++--------
>  tests/qemu-iotests/245.out |  4 ++--
>  2 files changed, 39 insertions(+), 12 deletions(-)
> 
> diff --git a/tests/qemu-iotests/245 b/tests/qemu-iotests/245
> index 489bf78bd0..7d9eb6285c 100755
> --- a/tests/qemu-iotests/245
> +++ b/tests/qemu-iotests/245
> @@ -970,8 +970,7 @@ class TestBlockdevReopen(iotests.QMPTestCase):
>          self.assertEqual(self.get_node('hd1'), None)
>          self.assert_qmp(self.get_node('hd2'), 'ro', True)
>  
> -    # We don't allow setting a backing file that uses a different AioContext
> -    def test_iothreads(self):
> +    def run_test_iothreads(self, iothread_a, iothread_b, errmsg = None):
>          opts = hd_opts(0)
>          result = self.vm.qmp('blockdev-add', conv_keys = False, **opts)
>          self.assert_qmp(result, 'return', {})
> @@ -986,20 +985,48 @@ class TestBlockdevReopen(iotests.QMPTestCase):
>          result = self.vm.qmp('object-add', qom_type='iothread', id='iothread1')
>          self.assert_qmp(result, 'return', {})
>  
> -        result = self.vm.qmp('x-blockdev-set-iothread', node_name='hd0', iothread='iothread0')
> +        result = self.vm.qmp('device_add', driver='virtio-scsi', id='scsi0',
> +                             iothread=iothread_a)
>          self.assert_qmp(result, 'return', {})
>  
> -        self.reopen(opts, {'backing': 'hd2'}, "Cannot use a new backing file with a different AioContext")
> -
> -        result = self.vm.qmp('x-blockdev-set-iothread', node_name='hd2', iothread='iothread1')
> +        result = self.vm.qmp('device_add', driver='virtio-scsi', id='scsi1',
> +                             iothread=iothread_b)
>          self.assert_qmp(result, 'return', {})
>  
> -        self.reopen(opts, {'backing': 'hd2'}, "Cannot use a new backing file with a different AioContext")
> +        if iothread_a:
> +            result = self.vm.qmp('device_add', driver='scsi-hd', drive='hd0',
> +                                 share_rw=True, bus="scsi0.0")
> +            self.assert_qmp(result, 'return', {})
>  
> -        result = self.vm.qmp('x-blockdev-set-iothread', node_name='hd2', iothread='iothread0')
> -        self.assert_qmp(result, 'return', {})
> +        if iothread_b:
> +            result = self.vm.qmp('device_add', driver='scsi-hd', drive='hd2',
> +                                 share_rw=True, bus="scsi1.0")
> +            self.assert_qmp(result, 'return', {})
>  
> -        self.reopen(opts, {'backing': 'hd2'})
> +        # Attaching the backing file may or may not work
> +        self.reopen(opts, {'backing': 'hd2'}, errmsg)
> +
> +        # But removing the backing file should always work
> +        self.reopen(opts, {'backing': None})
> +
> +        self.vm.shutdown()
> +
> +    # We don't allow setting a backing file that uses a different AioContext if
> +    # neither of them can switch to the other AioContext
> +    def test_iothreads_error(self):
> +        self.run_test_iothreads('iothread0', 'iothread1',
> +                                "Cannot use a new backing file with a different AioContext")
> +
> +    def test_iothreads_compatible_users(self):
> +        self.run_test_iothreads('iothread0', 'iothread0')
> +
> +    def test_iothreads_switch_backing(self):
> +        self.run_test_iothreads('iothread0', None,
> +                                "Cannot use a new backing file with a different AioContext")
> +
> +    def test_iothreads_switch_overlay(self):
> +        self.run_test_iothreads(None, 'iothread0',
> +                                "Cannot use a new backing file with a different AioContext")
>  
>  if __name__ == '__main__':
>      iotests.main(supported_fmts=["qcow2"],
> diff --git a/tests/qemu-iotests/245.out b/tests/qemu-iotests/245.out
> index a19de5214d..682b93394d 100644
> --- a/tests/qemu-iotests/245.out
> +++ b/tests/qemu-iotests/245.out
> @@ -1,6 +1,6 @@
> -..................
> +.....................
>  ----------------------------------------------------------------------
> -Ran 18 tests
> +Ran 21 tests
>  
>  OK
>  {"execute": "job-finalize", "arguments": {"id": "commit0"}}
> 

-- 
—js

[PATCH v2 2/2] block: bdrv_reopen() with backing file in different AioContext

[Kevin Wolf]

This patch allows bdrv_reopen() (and therefore the x-blockdev-reopen QMP
command) to attach a node as the new backing file even if the node is in
a different AioContext than the parent if one of both nodes can be moved
to the AioContext of the other node.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Tested-by: Peter Krempa <pkrempa@redhat.com>
---
 block.c                | 32 ++++++++++++++++++++++++++------
 tests/qemu-iotests/245 |  8 +++-----
 2 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/block.c b/block.c
index aaa387504e..957630b1c5 100644
--- a/block.c
+++ b/block.c
@@ -3787,6 +3787,29 @@ static void bdrv_reopen_perm(BlockReopenQueue *q, BlockDriverState *bs,
     *shared = cumulative_shared_perms;
 }
 
+static bool bdrv_reopen_can_attach(BlockDriverState *parent,
+                                   BdrvChild *child,
+                                   BlockDriverState *new_child,
+                                   Error **errp)
+{
+    AioContext *parent_ctx = bdrv_get_aio_context(parent);
+    AioContext *child_ctx = bdrv_get_aio_context(new_child);
+    GSList *ignore;
+    bool ret;
+
+    ignore = g_slist_prepend(NULL, child);
+    ret = bdrv_can_set_aio_context(new_child, parent_ctx, &ignore, NULL);
+    g_slist_free(ignore);
+    if (ret) {
+        return ret;
+    }
+
+    ignore = g_slist_prepend(NULL, child);
+    ret = bdrv_can_set_aio_context(parent, child_ctx, &ignore, errp);
+    g_slist_free(ignore);
+    return ret;
+}
+
 /*
  * Take a BDRVReopenState and check if the value of 'backing' in the
  * reopen_state->options QDict is valid or not.
@@ -3838,14 +3861,11 @@ static int bdrv_reopen_parse_backing(BDRVReopenState *reopen_state,
     }
 
     /*
-     * TODO: before removing the x- prefix from x-blockdev-reopen we
-     * should move the new backing file into the right AioContext
-     * instead of returning an error.
+     * Check AioContext compatibility so that the bdrv_set_backing_hd() call in
+     * bdrv_reopen_commit() won't fail.
      */
     if (new_backing_bs) {
-        if (bdrv_get_aio_context(new_backing_bs) != bdrv_get_aio_context(bs)) {
-            error_setg(errp, "Cannot use a new backing file "
-                       "with a different AioContext");
+        if (!bdrv_reopen_can_attach(bs, bs->backing, new_backing_bs, errp)) {
             return -EINVAL;
         }
     }
diff --git a/tests/qemu-iotests/245 b/tests/qemu-iotests/245
index 7d9eb6285c..1001275a44 100755
--- a/tests/qemu-iotests/245
+++ b/tests/qemu-iotests/245
@@ -1015,18 +1015,16 @@ class TestBlockdevReopen(iotests.QMPTestCase):
     # neither of them can switch to the other AioContext
     def test_iothreads_error(self):
         self.run_test_iothreads('iothread0', 'iothread1',
-                                "Cannot use a new backing file with a different AioContext")
+                                "Cannot change iothread of active block backend")
 
     def test_iothreads_compatible_users(self):
         self.run_test_iothreads('iothread0', 'iothread0')
 
     def test_iothreads_switch_backing(self):
-        self.run_test_iothreads('iothread0', None,
-                                "Cannot use a new backing file with a different AioContext")
+        self.run_test_iothreads('iothread0', None)
 
     def test_iothreads_switch_overlay(self):
-        self.run_test_iothreads(None, 'iothread0',
-                                "Cannot use a new backing file with a different AioContext")
+        self.run_test_iothreads(None, 'iothread0')
 
 if __name__ == '__main__':
     iotests.main(supported_fmts=["qcow2"],
-- 
2.20.1

Re: [PATCH v2 2/2] block: bdrv_reopen() with backing file in different AioContext

[Alberto Garcia]

On Fri 06 Mar 2020 03:14:13 PM CET, Kevin Wolf wrote:
> This patch allows bdrv_reopen() (and therefore the x-blockdev-reopen QMP
> command) to attach a node as the new backing file even if the node is in
> a different AioContext than the parent if one of both nodes can be moved
> to the AioContext of the other node.
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> Tested-by: Peter Krempa <pkrempa@redhat.com>

Reviewed-by: Alberto Garcia <berto@igalia.com>

Berto