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Blame SOURCES/kvm-block-bdrv_reopen-with-backing-file-in-different-Aio.patch

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From 1e0582ad34e77a060e2067a35992979c9eae82c9 Mon Sep 17 00:00:00 2001
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From: Kevin Wolf <kwolf@redhat.com>
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Date: Fri, 13 Mar 2020 12:34:31 +0000
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Subject: [PATCH 11/20] block: bdrv_reopen() with backing file in different
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 AioContext
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RH-Author: Kevin Wolf <kwolf@redhat.com>
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Message-id: <20200313123439.10548-6-kwolf@redhat.com>
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Patchwork-id: 94282
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O-Subject: [RHEL-AV-8.2.0 qemu-kvm PATCH v2 05/13] block: bdrv_reopen() with backing file in different AioContext
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Bugzilla: 1790482 1805143
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RH-Acked-by: John Snow <jsnow@redhat.com>
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RH-Acked-by: Daniel P. Berrange <berrange@redhat.com>
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RH-Acked-by: Peter Krempa <pkrempa@redhat.com>
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This patch allows bdrv_reopen() (and therefore the x-blockdev-reopen QMP
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command) to attach a node as the new backing file even if the node is in
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a different AioContext than the parent if one of both nodes can be moved
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to the AioContext of the other node.
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Tested-by: Peter Krempa <pkrempa@redhat.com>
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Message-Id: <20200306141413.30705-3-kwolf@redhat.com>
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Reviewed-by: Alberto Garcia <berto@igalia.com>
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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(cherry picked from commit 1de6b45fb5c1489b450df7d1a4c692bba9678ce6)
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
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---
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 block.c                | 32 ++++++++++++++++++++++++++------
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 tests/qemu-iotests/245 |  8 +++-----
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 2 files changed, 29 insertions(+), 11 deletions(-)
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diff --git a/block.c b/block.c
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index a744bb5..39e4647 100644
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--- a/block.c
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+++ b/block.c
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@@ -3749,6 +3749,29 @@ static void bdrv_reopen_perm(BlockReopenQueue *q, BlockDriverState *bs,
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     *shared = cumulative_shared_perms;
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 }
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+static bool bdrv_reopen_can_attach(BlockDriverState *parent,
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+                                   BdrvChild *child,
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+                                   BlockDriverState *new_child,
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+                                   Error **errp)
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+{
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+    AioContext *parent_ctx = bdrv_get_aio_context(parent);
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+    AioContext *child_ctx = bdrv_get_aio_context(new_child);
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+    GSList *ignore;
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+    bool ret;
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+
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+    ignore = g_slist_prepend(NULL, child);
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+    ret = bdrv_can_set_aio_context(new_child, parent_ctx, &ignore, NULL);
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+    g_slist_free(ignore);
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+    if (ret) {
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+        return ret;
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+    }
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+
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+    ignore = g_slist_prepend(NULL, child);
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+    ret = bdrv_can_set_aio_context(parent, child_ctx, &ignore, errp);
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+    g_slist_free(ignore);
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+    return ret;
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+}
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+
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 /*
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  * Take a BDRVReopenState and check if the value of 'backing' in the
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  * reopen_state->options QDict is valid or not.
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@@ -3800,14 +3823,11 @@ static int bdrv_reopen_parse_backing(BDRVReopenState *reopen_state,
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     }
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     /*
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-     * TODO: before removing the x- prefix from x-blockdev-reopen we
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-     * should move the new backing file into the right AioContext
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-     * instead of returning an error.
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+     * Check AioContext compatibility so that the bdrv_set_backing_hd() call in
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+     * bdrv_reopen_commit() won't fail.
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      */
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     if (new_backing_bs) {
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-        if (bdrv_get_aio_context(new_backing_bs) != bdrv_get_aio_context(bs)) {
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-            error_setg(errp, "Cannot use a new backing file "
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-                       "with a different AioContext");
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+        if (!bdrv_reopen_can_attach(bs, bs->backing, new_backing_bs, errp)) {
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             return -EINVAL;
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         }
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     }
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diff --git a/tests/qemu-iotests/245 b/tests/qemu-iotests/245
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index f69c2fa..919131d 100644
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--- a/tests/qemu-iotests/245
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+++ b/tests/qemu-iotests/245
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@@ -1013,18 +1013,16 @@ class TestBlockdevReopen(iotests.QMPTestCase):
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     # neither of them can switch to the other AioContext
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     def test_iothreads_error(self):
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         self.run_test_iothreads('iothread0', 'iothread1',
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-                                "Cannot use a new backing file with a different AioContext")
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+                                "Cannot change iothread of active block backend")
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     def test_iothreads_compatible_users(self):
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         self.run_test_iothreads('iothread0', 'iothread0')
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     def test_iothreads_switch_backing(self):
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-        self.run_test_iothreads('iothread0', None,
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-                                "Cannot use a new backing file with a different AioContext")
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+        self.run_test_iothreads('iothread0', None)
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     def test_iothreads_switch_overlay(self):
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-        self.run_test_iothreads(None, 'iothread0',
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-                                "Cannot use a new backing file with a different AioContext")
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+        self.run_test_iothreads(None, 'iothread0')
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 if __name__ == '__main__':
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     iotests.main(supported_fmts=["qcow2"],
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-- 
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1.8.3.1
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