From 2ed48247fd39ade97164dee3c65162b96a116f14 Mon Sep 17 00:00:00 2001

From: Hanna Reitz <hreitz@redhat.com>

Date: Fri, 4 Feb 2022 12:10:12 +0100

Subject: [PATCH 6/6] iotests/281: Let NBD connection yield in iothread

RH-Author: Hanna Reitz <hreitz@redhat.com>

RH-MergeRequest: 117: block/nbd: Handle AioContext changes

RH-Commit: [6/6] a23706f34022d301eb7ffc84fc0d0a77d72b9844

RH-Bugzilla: 2035185

RH-Acked-by: Kevin Wolf <kwolf@redhat.com>

RH-Acked-by: Eric Blake <eblake@redhat.com>

RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

Put an NBD block device into an I/O thread, and then read data from it,

hoping that the NBD connection will yield during that read.  When it

does, the coroutine must be reentered in the block device's I/O thread,

which will only happen if the NBD block driver attaches the connection's

QIOChannel to the new AioContext.  It did not do that after 4ddb5d2fde

("block/nbd: drop connection_co") and prior to "block/nbd: Move s->ioc

on AioContext change", which would cause an assertion failure.

To improve our chances of yielding, the NBD server is throttled to

reading 64 kB/s, and the NBD client reads 128 kB, so it should yield at

some point.

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

Signed-off-by: Hanna Reitz <hreitz@redhat.com>

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

(cherry picked from commit 8cfbe929e8c26050f0a4580a1606a370a947d4ce)

Signed-off-by: Hanna Reitz <hreitz@redhat.com>

---

 tests/qemu-iotests/281     | 28 +++++++++++++++++++++++++---

 tests/qemu-iotests/281.out |  4 ++--

 2 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/tests/qemu-iotests/281 b/tests/qemu-iotests/281

index 13c588be75..b2ead7f388 100755

--- a/tests/qemu-iotests/281

+++ b/tests/qemu-iotests/281

@@ -253,8 +253,9 @@ class TestYieldingAndTimers(iotests.QMPTestCase):

         self.create_nbd_export()

         # Simple VM with an NBD block device connected to the NBD export

-        # provided by the QSD

+        # provided by the QSD, and an (initially unused) iothread

         self.vm = iotests.VM()

+        self.vm.add_object('iothread,id=iothr')

         self.vm.add_blockdev('nbd,node-name=nbd,server.type=unix,' +

                              f'server.path={self.sock},export=exp,' +

                              'reconnect-delay=1')

@@ -293,19 +294,40 @@ class TestYieldingAndTimers(iotests.QMPTestCase):

         # thus not see the error, and so the test will pass.)

         time.sleep(2)

+    def test_yield_in_iothread(self):

+        # Move the NBD node to the I/O thread; the NBD block driver should

+        # attach the connection's QIOChannel to that thread's AioContext, too

+        result = self.vm.qmp('x-blockdev-set-iothread',

+                             node_name='nbd', iothread='iothr')

+        self.assert_qmp(result, 'return', {})

+

+        # Do some I/O that will be throttled by the QSD, so that the network

+        # connection hopefully will yield here.  When it is resumed, it must

+        # then be resumed in the I/O thread's AioContext.

+        result = self.vm.qmp('human-monitor-command',

+                             command_line='qemu-io nbd "read 0 128K"')

+        self.assert_qmp(result, 'return', '')

+

     def create_nbd_export(self):

         assert self.qsd is None

-        # Simple NBD export of a null-co BDS

+        # Export a throttled null-co BDS: Reads are throttled (max 64 kB/s),

+        # writes are not.

         self.qsd = QemuStorageDaemon(

+            '--object',

+            'throttle-group,id=thrgr,x-bps-read=65536,x-bps-read-max=65536',

+

             '--blockdev',

             'null-co,node-name=null,read-zeroes=true',

+            '--blockdev',

+            'throttle,node-name=thr,file=null,throttle-group=thrgr',

+

             '--nbd-server',

             f'addr.type=unix,addr.path={self.sock}',

             '--export',

-            'nbd,id=exp,node-name=null,name=exp,writable=true'

+            'nbd,id=exp,node-name=thr,name=exp,writable=true'

         )

     def stop_nbd_export(self):

diff --git a/tests/qemu-iotests/281.out b/tests/qemu-iotests/281.out

index 914e3737bd..3f8a935a08 100644

--- a/tests/qemu-iotests/281.out

+++ b/tests/qemu-iotests/281.out

@@ -1,5 +1,5 @@

-.....

+......

 ----------------------------------------------------------------------

-Ran 5 tests

+Ran 6 tests

 OK

-- 

2.27.0