[v2,04/31] block/export: Add BlockExport infrastructure and block-export-add

diff --git a/qapi/block-export.json b/qapi/block-export.json
index d540bcb25a..71c5730bc0 100644
--- a/qapi/block-export.json
+++ b/qapi/block-export.json
@@ -173,3 +173,12 @@ 
       'nbd': 'BlockExportOptionsNbd'
    } }
 
+##
+# @block-export-add:
+#
+# Creates a new block export.
+#
+# Since: 5.2
+##
+{ 'command': 'block-export-add',
+  'data': 'BlockExportOptions', 'boxed': true }
diff --git a/include/block/export.h b/include/block/export.h
new file mode 100644
index 0000000000..42e3c055fc
--- /dev/null
+++ b/include/block/export.h
@@ -0,0 +1,33 @@ 
+/*
+ * Declarations for block exports
+ *
+ * Copyright (c) 2012, 2020 Red Hat, Inc.
+ *
+ * Authors:
+ * Paolo Bonzini <pbonzini@redhat.com>
+ * Kevin Wolf <kwolf@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * later.  See the COPYING file in the top-level directory.
+ */
+
+#ifndef BLOCK_EXPORT_H
+#define BLOCK_EXPORT_H
+
+#include "qapi/qapi-types-block-export.h"
+
+typedef struct BlockExport BlockExport;
+
+typedef struct BlockExportDriver {
+    /* The export type that this driver services */
+    BlockExportType type;
+
+    /* Creates and starts a new block export */
+    BlockExport *(*create)(BlockExportOptions *, Error **);
+} BlockExportDriver;
+
+struct BlockExport {
+    const BlockExportDriver *drv;
+};
+
+#endif
diff --git a/include/block/nbd.h b/include/block/nbd.h
index 262f6da2ce..7698453fb2 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -20,11 +20,13 @@ 
 #ifndef NBD_H
 #define NBD_H
 
-#include "qapi/qapi-types-block-export.h"
+#include "block/export.h"
 #include "io/channel-socket.h"
 #include "crypto/tlscreds.h"
 #include "qapi/error.h"
 
+extern const BlockExportDriver blk_exp_nbd;
+
 /* Handshake phase structs - this struct is passed on the wire */
 
 struct NBDOption {
@@ -328,6 +330,7 @@  int nbd_errno_to_system_errno(int err);
 typedef struct NBDExport NBDExport;
 typedef struct NBDClient NBDClient;
 
+BlockExport *nbd_export_create(BlockExportOptions *exp_args, Error **errp);
 NBDExport *nbd_export_new(BlockDriverState *bs, uint64_t dev_offset,
                           uint64_t size, const char *name, const char *desc,
                           const char *bitmap, bool readonly, bool shared,
diff --git a/block/export/export.c b/block/export/export.c
new file mode 100644
index 0000000000..fd65541963
--- /dev/null
+++ b/block/export/export.c
@@ -0,0 +1,48 @@ 
+/*
+ * Common block export infrastructure
+ *
+ * Copyright (c) 2012, 2020 Red Hat, Inc.
+ *
+ * Authors:
+ * Paolo Bonzini <pbonzini@redhat.com>
+ * Kevin Wolf <kwolf@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * later.  See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+
+#include "block/export.h"
+#include "block/nbd.h"
+#include "qapi/error.h"
+#include "qapi/qapi-commands-block-export.h"
+
+static const BlockExportDriver *blk_exp_drivers[] = {
+    &blk_exp_nbd,
+};
+
+static const BlockExportDriver *blk_exp_find_driver(BlockExportType type)
+{
+    int i;
+
+    for (i = 0; i < ARRAY_SIZE(blk_exp_drivers); i++) {
+        if (blk_exp_drivers[i]->type == type) {
+            return blk_exp_drivers[i];
+        }
+    }
+    return NULL;
+}
+
+void qmp_block_export_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;
+    }
+
+    drv->create(export, errp);
+}
diff --git a/blockdev-nbd.c b/blockdev-nbd.c
index 98ee1b6170..47b04f166a 100644
--- a/blockdev-nbd.c
+++ b/blockdev-nbd.c
@@ -148,17 +148,20 @@  void qmp_nbd_server_start(SocketAddressLegacy *addr,
     qapi_free_SocketAddress(addr_flat);
 }
 
-void qmp_nbd_server_add(BlockExportOptionsNbd *arg, Error **errp)
+BlockExport *nbd_export_create(BlockExportOptions *exp_args, Error **errp)
 {
+    BlockExportOptionsNbd *arg = &exp_args->u.nbd;
     BlockDriverState *bs = NULL;
     BlockBackend *on_eject_blk;
-    NBDExport *exp;
+    NBDExport *exp = NULL;
     int64_t len;
     AioContext *aio_context;
 
+    assert(exp_args->type == BLOCK_EXPORT_TYPE_NBD);
+
     if (!nbd_server) {
         error_setg(errp, "NBD server not running");
-        return;
+        return NULL;
     }
 
     if (!arg->has_name) {
@@ -167,24 +170,24 @@  void qmp_nbd_server_add(BlockExportOptionsNbd *arg, Error **errp)
 
     if (strlen(arg->name) > NBD_MAX_STRING_SIZE) {
         error_setg(errp, "export name '%s' too long", arg->name);
-        return;
+        return NULL;
     }
 
     if (arg->description && strlen(arg->description) > NBD_MAX_STRING_SIZE) {
         error_setg(errp, "description '%s' too long", arg->description);
-        return;
+        return NULL;
     }
 
     if (nbd_export_find(arg->name)) {
         error_setg(errp, "NBD server already has export named '%s'", arg->name);
-        return;
+        return NULL;
     }
 
     on_eject_blk = blk_by_name(arg->device);
 
     bs = bdrv_lookup_bs(arg->device, arg->device, errp);
     if (!bs) {
-        return;
+        return NULL;
     }
 
     aio_context = bdrv_get_aio_context(bs);
@@ -217,6 +220,17 @@  void qmp_nbd_server_add(BlockExportOptionsNbd *arg, Error **errp)
 
  out:
     aio_context_release(aio_context);
+    /* TODO Remove the cast: nbd_export_new() will return a BlockExport. */
+    return (BlockExport*) exp;
+}
+
+void qmp_nbd_server_add(BlockExportOptionsNbd *arg, Error **errp)
+{
+    BlockExportOptions export = {
+        .type = BLOCK_EXPORT_TYPE_NBD,
+        .u.nbd = *arg,
+    };
+    qmp_block_export_add(&export, errp);
 }
 
 void qmp_nbd_server_remove(const char *name,
diff --git a/nbd/server.c b/nbd/server.c
index bd53f7baea..f5af93c253 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -18,6 +18,8 @@ 
  */
 
 #include "qemu/osdep.h"
+
+#include "block/export.h"
 #include "qapi/error.h"
 #include "qemu/queue.h"
 #include "trace.h"
@@ -80,6 +82,7 @@  struct NBDRequestData {
 };
 
 struct NBDExport {
+    BlockExport common;
     int refcount;
     void (*close)(NBDExport *exp);
 
@@ -1512,10 +1515,15 @@  NBDExport *nbd_export_new(BlockDriverState *bs, uint64_t dev_offset,
 {
     AioContext *ctx;
     BlockBackend *blk;
-    NBDExport *exp = g_new0(NBDExport, 1);
+    NBDExport *exp;
     uint64_t perm;
     int ret;
 
+    exp = g_new0(NBDExport, 1);
+    exp->common = (BlockExport) {
+        .drv = &blk_exp_nbd,
+    };
+
     /*
      * NBD exports are used for non-shared storage migration.  Make sure
      * that BDRV_O_INACTIVE is cleared and the image is ready for write
@@ -1731,6 +1739,11 @@  void nbd_export_put(NBDExport *exp)
     }
 }
 
+const BlockExportDriver blk_exp_nbd = {
+    .type               = BLOCK_EXPORT_TYPE_NBD,
+    .create             = nbd_export_create,
+};
+
 void nbd_export_close_all(void)
 {
     NBDExport *exp, *next;
diff --git a/block/export/meson.build b/block/export/meson.build
new file mode 100644
index 0000000000..558ef35d38
--- /dev/null
+++ b/block/export/meson.build
@@ -0,0 +1 @@ 
+block_ss.add(files('export.c'))
diff --git a/block/meson.build b/block/meson.build
index a3e56b7cd1..0b38dc36f7 100644
--- a/block/meson.build
+++ b/block/meson.build
@@ -110,6 +110,8 @@  block_ss.add(module_block_h)
 block_ss.add(files('stream.c'))
 
 softmmu_ss.add(files('qapi-sysemu.c'))
+
+subdir('export')
 subdir('monitor')
 
 modules += {'block': block_modules}
diff --git a/meson.build b/meson.build
index f4d1ab1096..4c6c7310fa 100644
--- a/meson.build
+++ b/meson.build
@@ -830,6 +830,7 @@  subdir('dump')
 
 block_ss.add(files(
   'block.c',
+  'blockdev-nbd.c',
   'blockjob.c',
   'job.c',
   'qemu-io-cmds.c',
@@ -842,7 +843,6 @@  subdir('block')
 
 blockdev_ss.add(files(
   'blockdev.c',
-  'blockdev-nbd.c',
   'iothread.c',
   'job-qmp.c',
 ))