[PULL,11/37] block/export: Remove magic from block-export-add

diff --git a/include/block/export.h b/include/block/export.h
index 42e3c055fc..e7af2c7687 100644
--- a/include/block/export.h
+++ b/include/block/export.h
@@ -30,4 +30,6 @@  struct BlockExport {
     const BlockExportDriver *drv;
 };
 
+BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp);
+
 #endif
diff --git a/include/block/nbd.h b/include/block/nbd.h
index 451f399b0a..f55f5b710b 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -335,7 +335,8 @@  NBDExport *nbd_export_new(BlockDriverState *bs,
                           const char *name, const char *desc,
                           const char *bitmap, bool readonly, bool shared,
                           void (*close)(NBDExport *), bool writethrough,
-                          BlockBackend *on_eject_blk, Error **errp);
+                          Error **errp);
+void nbd_export_set_on_eject_blk(BlockExport *exp, BlockBackend *blk);
 void nbd_export_close(NBDExport *exp);
 void nbd_export_remove(NBDExport *exp, NbdServerRemoveMode mode, Error **errp);
 void nbd_export_get(NBDExport *exp);
diff --git a/block/export/export.c b/block/export/export.c
index fd65541963..05bc5e3744 100644
--- a/block/export/export.c
+++ b/block/export/export.c
@@ -13,6 +13,8 @@ 
 
 #include "qemu/osdep.h"
 
+#include "block/block.h"
+#include "sysemu/block-backend.h"
 #include "block/export.h"
 #include "block/nbd.h"
 #include "qapi/error.h"
@@ -34,15 +36,20 @@  static const BlockExportDriver *blk_exp_find_driver(BlockExportType type)
     return NULL;
 }
 
-void qmp_block_export_add(BlockExportOptions *export, Error **errp)
+BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
 {
     const BlockExportDriver *drv;
 
     drv = blk_exp_find_driver(export->type);
     if (!drv) {
         error_setg(errp, "No driver found for the requested export type");
-        return;
+        return NULL;
     }
 
-    drv->create(export, errp);
+    return drv->create(export, errp);
+}
+
+void qmp_block_export_add(BlockExportOptions *export, Error **errp)
+{
+    blk_exp_add(export, errp);
 }
diff --git a/blockdev-nbd.c b/blockdev-nbd.c
index 96cb0100e9..7bcca105f9 100644
--- a/blockdev-nbd.c
+++ b/blockdev-nbd.c
@@ -152,7 +152,6 @@  BlockExport *nbd_export_create(BlockExportOptions *exp_args, Error **errp)
 {
     BlockExportOptionsNbd *arg = &exp_args->u.nbd;
     BlockDriverState *bs = NULL;
-    BlockBackend *on_eject_blk;
     NBDExport *exp = NULL;
     AioContext *aio_context;
 
@@ -182,8 +181,6 @@  BlockExport *nbd_export_create(BlockExportOptions *exp_args, Error **errp)
         return NULL;
     }
 
-    on_eject_blk = blk_by_name(arg->device);
-
     bs = bdrv_lookup_bs(arg->device, arg->device, errp);
     if (!bs) {
         return NULL;
@@ -195,13 +192,14 @@  BlockExport *nbd_export_create(BlockExportOptions *exp_args, Error **errp)
     if (!arg->has_writable) {
         arg->writable = false;
     }
-    if (bdrv_is_read_only(bs)) {
-        arg->writable = false;
+    if (bdrv_is_read_only(bs) && arg->writable) {
+        error_setg(errp, "Cannot export read-only node as writable");
+        goto out;
     }
 
     exp = nbd_export_new(bs, arg->name, arg->description, arg->bitmap,
                          !arg->writable, !arg->writable,
-                         NULL, false, on_eject_blk, errp);
+                         NULL, false, errp);
     if (!exp) {
         goto out;
     }
@@ -219,11 +217,44 @@  BlockExport *nbd_export_create(BlockExportOptions *exp_args, Error **errp)
 
 void qmp_nbd_server_add(BlockExportOptionsNbd *arg, Error **errp)
 {
-    BlockExportOptions export = {
+    BlockExport *export;
+    BlockDriverState *bs;
+    BlockBackend *on_eject_blk;
+    BlockExportOptions export_opts;
+
+    bs = bdrv_lookup_bs(arg->device, arg->device, errp);
+    if (!bs) {
+        return;
+    }
+
+    export_opts = (BlockExportOptions) {
         .type = BLOCK_EXPORT_TYPE_NBD,
         .u.nbd = *arg,
     };
-    qmp_block_export_add(&export, errp);
+
+    /*
+     * nbd-server-add doesn't complain when a read-only device should be
+     * exported as writable, but simply downgrades it. This is an error with
+     * block-export-add.
+     */
+    if (bdrv_is_read_only(bs)) {
+        export_opts.u.nbd.has_writable = true;
+        export_opts.u.nbd.writable = false;
+    }
+
+    export = blk_exp_add(&export_opts, errp);
+    if (!export) {
+        return;
+    }
+
+    /*
+     * nbd-server-add removes the export when the named BlockBackend used for
+     * @device goes away.
+     */
+    on_eject_blk = blk_by_name(arg->device);
+    if (on_eject_blk) {
+        nbd_export_set_on_eject_blk(export, on_eject_blk);
+    }
 }
 
 void qmp_nbd_server_remove(const char *name,
diff --git a/nbd/server.c b/nbd/server.c
index 33aaca918c..23d9a53094 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -1506,11 +1506,23 @@  static void nbd_eject_notifier(Notifier *n, void *data)
     aio_context_release(aio_context);
 }
 
+void nbd_export_set_on_eject_blk(BlockExport *exp, BlockBackend *blk)
+{
+    NBDExport *nbd_exp = container_of(exp, NBDExport, common);
+    assert(exp->drv == &blk_exp_nbd);
+    assert(nbd_exp->eject_notifier_blk == NULL);
+
+    blk_ref(blk);
+    nbd_exp->eject_notifier_blk = blk;
+    nbd_exp->eject_notifier.notify = nbd_eject_notifier;
+    blk_add_remove_bs_notifier(blk, &nbd_exp->eject_notifier);
+}
+
 NBDExport *nbd_export_new(BlockDriverState *bs,
                           const char *name, const char *desc,
                           const char *bitmap, bool readonly, bool shared,
                           void (*close)(NBDExport *), bool writethrough,
-                          BlockBackend *on_eject_blk, Error **errp)
+                          Error **errp)
 {
     AioContext *ctx;
     BlockBackend *blk;
@@ -1617,12 +1629,6 @@  NBDExport *nbd_export_new(BlockDriverState *bs,
     exp->ctx = ctx;
     blk_add_aio_context_notifier(blk, blk_aio_attached, blk_aio_detach, exp);
 
-    if (on_eject_blk) {
-        blk_ref(on_eject_blk);
-        exp->eject_notifier_blk = on_eject_blk;
-        exp->eject_notifier.notify = nbd_eject_notifier;
-        blk_add_remove_bs_notifier(on_eject_blk, &exp->eject_notifier);
-    }
     QTAILQ_INSERT_TAIL(&exports, exp, next);
     nbd_export_get(exp);
     return exp;
diff --git a/qemu-nbd.c b/qemu-nbd.c
index 16473d809c..b2a0ea6c5e 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -1067,8 +1067,7 @@  int main(int argc, char **argv)
 
     export = nbd_export_new(bs, export_name,
                             export_description, bitmap, readonly, shared > 1,
-                            nbd_export_closed, writethrough, NULL,
-                            &error_fatal);
+                            nbd_export_closed, writethrough, &error_fatal);
 
     if (device) {
 #if HAVE_NBD_DEVICE