[PATCH 4/4] block/export: add BlockExportOptions->iothread member

[Stefan Hajnoczi <stefanha@redhat.com>]

Make it possible to specify the iothread where the export will run.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
Note the x-blockdev-set-iothread QMP command can be used to do the same,
but not from the command-line. And it requires sending an additional
command.

In the long run vhost-user-blk will support per-virtqueue iothread
mappings. But for now a single iothread makes sense and most other
transports will just use one iothread anyway.
---
 qapi/block-export.json |  4 ++++
 block/export/export.c  | 26 +++++++++++++++++++++++++-
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/qapi/block-export.json b/qapi/block-export.json
index 87ac5117cd..eba6f6eae9 100644
--- a/qapi/block-export.json
+++ b/qapi/block-export.json
@@ -219,11 +219,15 @@
 #                export before completion is signalled. (since: 5.2;
 #                default: false)
 #
+# @iothread: The name of the iothread object where the export will run. The
+#            default is the main loop thread. (since: 5.2)
+#
 # Since: 4.2
 ##
 { 'union': 'BlockExportOptions',
   'base': { 'type': 'BlockExportType',
             'id': 'str',
+	    '*iothread': 'str',
             'node-name': 'str',
             '*writable': 'bool',
             '*writethrough': 'bool' },
diff --git a/block/export/export.c b/block/export/export.c
index 550897e236..0fb3d76ee3 100644
--- a/block/export/export.c
+++ b/block/export/export.c
@@ -15,6 +15,7 @@
 
 #include "block/block.h"
 #include "sysemu/block-backend.h"
+#include "sysemu/iothread.h"
 #include "block/export.h"
 #include "block/nbd.h"
 #include "qapi/error.h"
@@ -66,7 +67,7 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
     const BlockExportDriver *drv;
     BlockExport *exp = NULL;
     BlockDriverState *bs;
-    BlockBackend *blk;
+    BlockBackend *blk = NULL;
     AioContext *ctx;
     uint64_t perm;
     int ret;
@@ -102,6 +103,29 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
     ctx = bdrv_get_aio_context(bs);
     aio_context_acquire(ctx);
 
+    if (export->has_iothread) {
+        IOThread *iothread;
+        AioContext *new_ctx;
+
+        iothread = iothread_by_id(export->iothread);
+        if (!iothread) {
+            error_setg(errp, "iothread \"%s\" not found", export->iothread);
+            goto fail;
+        }
+
+        new_ctx = iothread_get_aio_context(iothread);
+
+        ret = bdrv_try_set_aio_context(bs, new_ctx, errp);
+        if (ret != 0) {
+            goto fail;
+        }
+
+        aio_context_release(ctx);
+        aio_context_acquire(new_ctx);
+
+        ctx = new_ctx;
+    }
+
     /*
      * Block exports are used for non-shared storage migration. Make sure
      * that BDRV_O_INACTIVE is cleared and the image is ready for write
-- 
2.26.2