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Blame SOURCES/kvm-test-bdrv-drain-bdrv_drain-works-with-cross-AioConte.patch

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From ae1deee29ac316ea755c96f15b739db7a59e5c61 Mon Sep 17 00:00:00 2001
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From: Kevin Wolf <kwolf@redhat.com>
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Date: Wed, 10 Oct 2018 20:08:35 +0100
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Subject: [PATCH 04/49] test-bdrv-drain: bdrv_drain() works with
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 cross-AioContext events
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RH-Author: Kevin Wolf <kwolf@redhat.com>
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Message-id: <20181010200843.6710-2-kwolf@redhat.com>
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Patchwork-id: 82581
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O-Subject: [RHEL-8 qemu-kvm PATCH 01/44] test-bdrv-drain: bdrv_drain() works with cross-AioContext events
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Bugzilla: 1637976
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RH-Acked-by: Max Reitz <mreitz@redhat.com>
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RH-Acked-by: John Snow <jsnow@redhat.com>
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RH-Acked-by: Thomas Huth <thuth@redhat.com>
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As long as nobody keeps the other I/O thread from working, there is no
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reason why bdrv_drain() wouldn't work with cross-AioContext events. The
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key is that the root request we're waiting for is in the AioContext
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we're polling (which it always is for bdrv_drain()) so that aio_poll()
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is woken up in the end.
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Add a test case that shows that it works. Remove the comment in
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bdrv_drain() that claims otherwise.
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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(cherry picked from commit bb6756895459f181e2f25e877d3d7a10c297b5c8)
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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/io.c              |   4 --
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 tests/test-bdrv-drain.c | 187 +++++++++++++++++++++++++++++++++++++++++++++++-
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 2 files changed, 186 insertions(+), 5 deletions(-)
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diff --git a/block/io.c b/block/io.c
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index bb617de..7e0a169 100644
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--- a/block/io.c
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+++ b/block/io.c
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@@ -369,10 +369,6 @@ void bdrv_unapply_subtree_drain(BdrvChild *child, BlockDriverState *old_parent)
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  *
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  * Note that unlike bdrv_drain_all(), the caller must hold the BlockDriverState
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  * AioContext.
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- *
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- * Only this BlockDriverState's AioContext is run, so in-flight requests must
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- * not depend on events in other AioContexts.  In that case, use
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- * bdrv_drain_all() instead.
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  */
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 void coroutine_fn bdrv_co_drain(BlockDriverState *bs)
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 {
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diff --git a/tests/test-bdrv-drain.c b/tests/test-bdrv-drain.c
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index 403446e..dee0a10 100644
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--- a/tests/test-bdrv-drain.c
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+++ b/tests/test-bdrv-drain.c
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@@ -27,9 +27,13 @@
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 #include "block/blockjob_int.h"
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 #include "sysemu/block-backend.h"
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 #include "qapi/error.h"
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+#include "iothread.h"
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+
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+static QemuEvent done_event;
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 typedef struct BDRVTestState {
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     int drain_count;
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+    AioContext *bh_indirection_ctx;
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 } BDRVTestState;
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 static void coroutine_fn bdrv_test_co_drain_begin(BlockDriverState *bs)
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@@ -50,16 +54,29 @@ static void bdrv_test_close(BlockDriverState *bs)
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     g_assert_cmpint(s->drain_count, >, 0);
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 }
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+static void co_reenter_bh(void *opaque)
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+{
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+    aio_co_wake(opaque);
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+}
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+
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 static int coroutine_fn bdrv_test_co_preadv(BlockDriverState *bs,
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                                             uint64_t offset, uint64_t bytes,
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                                             QEMUIOVector *qiov, int flags)
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 {
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+    BDRVTestState *s = bs->opaque;
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+
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     /* We want this request to stay until the polling loop in drain waits for
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      * it to complete. We need to sleep a while as bdrv_drain_invoke() comes
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      * first and polls its result, too, but it shouldn't accidentally complete
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      * this request yet. */
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     qemu_co_sleep_ns(QEMU_CLOCK_REALTIME, 100000);
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+    if (s->bh_indirection_ctx) {
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+        aio_bh_schedule_oneshot(s->bh_indirection_ctx, co_reenter_bh,
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+                                qemu_coroutine_self());
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+        qemu_coroutine_yield();
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+    }
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+
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     return 0;
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 }
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@@ -490,6 +507,164 @@ static void test_graph_change(void)
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     blk_unref(blk_b);
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 }
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+struct test_iothread_data {
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+    BlockDriverState *bs;
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+    enum drain_type drain_type;
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+    int *aio_ret;
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+};
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+
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+static void test_iothread_drain_entry(void *opaque)
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+{
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+    struct test_iothread_data *data = opaque;
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+
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+    aio_context_acquire(bdrv_get_aio_context(data->bs));
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+    do_drain_begin(data->drain_type, data->bs);
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+    g_assert_cmpint(*data->aio_ret, ==, 0);
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+    do_drain_end(data->drain_type, data->bs);
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+    aio_context_release(bdrv_get_aio_context(data->bs));
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+
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+    qemu_event_set(&done_event);
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+}
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+
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+static void test_iothread_aio_cb(void *opaque, int ret)
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+{
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+    int *aio_ret = opaque;
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+    *aio_ret = ret;
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+    qemu_event_set(&done_event);
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+}
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+
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+/*
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+ * Starts an AIO request on a BDS that runs in the AioContext of iothread 1.
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+ * The request involves a BH on iothread 2 before it can complete.
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+ *
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+ * @drain_thread = 0 means that do_drain_begin/end are called from the main
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+ * thread, @drain_thread = 1 means that they are called from iothread 1. Drain
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+ * for this BDS cannot be called from iothread 2 because only the main thread
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+ * may do cross-AioContext polling.
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+ */
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+static void test_iothread_common(enum drain_type drain_type, int drain_thread)
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+{
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+    BlockBackend *blk;
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+    BlockDriverState *bs;
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+    BDRVTestState *s;
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+    BlockAIOCB *acb;
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+    int aio_ret;
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+    struct test_iothread_data data;
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+
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+    IOThread *a = iothread_new();
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+    IOThread *b = iothread_new();
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+    AioContext *ctx_a = iothread_get_aio_context(a);
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+    AioContext *ctx_b = iothread_get_aio_context(b);
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+
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+    QEMUIOVector qiov;
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+    struct iovec iov = {
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+        .iov_base = NULL,
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+        .iov_len = 0,
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+    };
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+    qemu_iovec_init_external(&qiov, &iov, 1);
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+
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+    /* bdrv_drain_all() may only be called from the main loop thread */
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+    if (drain_type == BDRV_DRAIN_ALL && drain_thread != 0) {
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+        goto out;
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+    }
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+
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+    blk = blk_new(BLK_PERM_ALL, BLK_PERM_ALL);
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+    bs = bdrv_new_open_driver(&bdrv_test, "test-node", BDRV_O_RDWR,
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+                              &error_abort);
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+    s = bs->opaque;
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+    blk_insert_bs(blk, bs, &error_abort);
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+
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+    blk_set_aio_context(blk, ctx_a);
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+    aio_context_acquire(ctx_a);
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+
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+    s->bh_indirection_ctx = ctx_b;
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+
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+    aio_ret = -EINPROGRESS;
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+    if (drain_thread == 0) {
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+        acb = blk_aio_preadv(blk, 0, &qiov, 0, test_iothread_aio_cb, &aio_ret);
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+    } else {
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+        acb = blk_aio_preadv(blk, 0, &qiov, 0, aio_ret_cb, &aio_ret);
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+    }
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+    g_assert(acb != NULL);
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+    g_assert_cmpint(aio_ret, ==, -EINPROGRESS);
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+
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+    aio_context_release(ctx_a);
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+
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+    data = (struct test_iothread_data) {
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+        .bs         = bs,
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+        .drain_type = drain_type,
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+        .aio_ret    = &aio_ret,
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+    };
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+
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+    switch (drain_thread) {
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+    case 0:
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+        if (drain_type != BDRV_DRAIN_ALL) {
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+            aio_context_acquire(ctx_a);
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+        }
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+
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+        /* The request is running on the IOThread a. Draining its block device
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+         * will make sure that it has completed as far as the BDS is concerned,
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+         * but the drain in this thread can continue immediately after
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+         * bdrv_dec_in_flight() and aio_ret might be assigned only slightly
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+         * later. */
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+        qemu_event_reset(&done_event);
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+        do_drain_begin(drain_type, bs);
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+        g_assert_cmpint(bs->in_flight, ==, 0);
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+
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+        if (drain_type != BDRV_DRAIN_ALL) {
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+            aio_context_release(ctx_a);
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+        }
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+        qemu_event_wait(&done_event);
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+        if (drain_type != BDRV_DRAIN_ALL) {
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+            aio_context_acquire(ctx_a);
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+        }
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+
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+        g_assert_cmpint(aio_ret, ==, 0);
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+        do_drain_end(drain_type, bs);
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+
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+        if (drain_type != BDRV_DRAIN_ALL) {
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+            aio_context_release(ctx_a);
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+        }
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+        break;
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+    case 1:
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+        qemu_event_reset(&done_event);
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+        aio_bh_schedule_oneshot(ctx_a, test_iothread_drain_entry, &data);
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+        qemu_event_wait(&done_event);
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+        break;
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+    default:
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+        g_assert_not_reached();
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+    }
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+
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+    aio_context_acquire(ctx_a);
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+    blk_set_aio_context(blk, qemu_get_aio_context());
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+    aio_context_release(ctx_a);
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+
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+    bdrv_unref(bs);
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+    blk_unref(blk);
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+
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+out:
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+    iothread_join(a);
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+    iothread_join(b);
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+}
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+
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+static void test_iothread_drain_all(void)
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+{
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+    test_iothread_common(BDRV_DRAIN_ALL, 0);
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+    test_iothread_common(BDRV_DRAIN_ALL, 1);
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+}
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+
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+static void test_iothread_drain(void)
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+{
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+    test_iothread_common(BDRV_DRAIN, 0);
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+    test_iothread_common(BDRV_DRAIN, 1);
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+}
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+
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+static void test_iothread_drain_subtree(void)
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+{
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+    test_iothread_common(BDRV_SUBTREE_DRAIN, 0);
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+    test_iothread_common(BDRV_SUBTREE_DRAIN, 1);
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+}
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+
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 typedef struct TestBlockJob {
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     BlockJob common;
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@@ -613,10 +788,13 @@ static void test_blockjob_drain_subtree(void)
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 int main(int argc, char **argv)
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 {
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+    int ret;
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+
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     bdrv_init();
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     qemu_init_main_loop(&error_abort);
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     g_test_init(&argc, &argv, NULL);
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+    qemu_event_init(&done_event, false);
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     g_test_add_func("/bdrv-drain/driver-cb/drain_all", test_drv_cb_drain_all);
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     g_test_add_func("/bdrv-drain/driver-cb/drain", test_drv_cb_drain);
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@@ -643,10 +821,17 @@ int main(int argc, char **argv)
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     g_test_add_func("/bdrv-drain/multiparent", test_multiparent);
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     g_test_add_func("/bdrv-drain/graph-change", test_graph_change);
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+    g_test_add_func("/bdrv-drain/iothread/drain_all", test_iothread_drain_all);
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+    g_test_add_func("/bdrv-drain/iothread/drain", test_iothread_drain);
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+    g_test_add_func("/bdrv-drain/iothread/drain_subtree",
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+                    test_iothread_drain_subtree);
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+
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     g_test_add_func("/bdrv-drain/blockjob/drain_all", test_blockjob_drain_all);
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     g_test_add_func("/bdrv-drain/blockjob/drain", test_blockjob_drain);
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     g_test_add_func("/bdrv-drain/blockjob/drain_subtree",
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                     test_blockjob_drain_subtree);
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-    return g_test_run();
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+    ret = g_test_run();
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+    qemu_event_destroy(&done_event);
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+    return ret;
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 }
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-- 
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1.8.3.1
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