From f51d23c80af73c95e0ce703ad06a300f1b3d63ef Mon Sep 17 00:00:00 2001
From: Stefan Hajnoczi <stefanha@redhat.com>
Date: Tue, 29 Sep 2020 13:55:16 +0100
Subject: block/export: add iothread and fixed-iothread options

Make it possible to specify the iothread where the export will run. By
default the block node can be moved to other AioContexts later and the
export will follow. The fixed-iothread option forces strict behavior
that prevents changing AioContext while the export is active. See the
QAPI docs for details.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20200929125516.186715-5-stefanha@redhat.com
[Fix stray '#' character in block-export.json and add missing "(since:
5.2)" as suggested by Eric Blake.
--Stefan]
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 block/export/export.c                | 31 ++++++++++++++++++++++++++++++-
 block/export/vhost-user-blk-server.c |  5 ++++-
 2 files changed, 34 insertions(+), 2 deletions(-)

(limited to 'block/export')

diff --git a/block/export/export.c b/block/export/export.c
index a24fadcfb5..c3478c6c97 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"
@@ -63,10 +64,11 @@ static const BlockExportDriver *blk_exp_find_driver(BlockExportType type)
 
 BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
 {
+    bool fixed_iothread = export->has_fixed_iothread && export->fixed_iothread;
     const BlockExportDriver *drv;
     BlockExport *exp = NULL;
     BlockDriverState *bs;
-    BlockBackend *blk;
+    BlockBackend *blk = NULL;
     AioContext *ctx;
     uint64_t perm;
     int ret;
@@ -102,6 +104,28 @@ 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) {
+            aio_context_release(ctx);
+            aio_context_acquire(new_ctx);
+            ctx = new_ctx;
+        } else if (fixed_iothread) {
+            goto fail;
+        }
+    }
+
     /*
      * Block exports are used for non-shared storage migration. Make sure
      * that BDRV_O_INACTIVE is cleared and the image is ready for write
@@ -116,6 +140,11 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
     }
 
     blk = blk_new(ctx, perm, BLK_PERM_ALL);
+
+    if (!fixed_iothread) {
+        blk_set_allow_aio_context_change(blk, true);
+    }
+
     ret = blk_insert_bs(blk, bs, errp);
     if (ret < 0) {
         goto fail;
diff --git a/block/export/vhost-user-blk-server.c b/block/export/vhost-user-blk-server.c
index f7021cbd7b..286eb5fb9a 100644
--- a/block/export/vhost-user-blk-server.c
+++ b/block/export/vhost-user-blk-server.c
@@ -323,13 +323,17 @@ static const VuDevIface vu_blk_iface = {
 static void blk_aio_attached(AioContext *ctx, void *opaque)
 {
     VuBlkExport *vexp = opaque;
+
+    vexp->export.ctx = ctx;
     vhost_user_server_attach_aio_context(&vexp->vu_server, ctx);
 }
 
 static void blk_aio_detach(void *opaque)
 {
     VuBlkExport *vexp = opaque;
+
     vhost_user_server_detach_aio_context(&vexp->vu_server);
+    vexp->export.ctx = NULL;
 }
 
 static void
@@ -384,7 +388,6 @@ static int vu_blk_exp_create(BlockExport *exp, BlockExportOptions *opts,
     vu_blk_initialize_config(blk_bs(exp->blk), &vexp->blkcfg,
                                logical_block_size);
 
-    blk_set_allow_aio_context_change(exp->blk, true);
     blk_add_aio_context_notifier(exp->blk, blk_aio_attached, blk_aio_detach,
                                  vexp);
 
-- 
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