block/export: Add BlockExport infrastructure and block-export-add

We want to have a common set of commands for all types of block exports.
Currently, this is only NBD, but we're going to add more types.

This patch adds the basic BlockExport and BlockExportDriver structs and
a QMP command block-export-add that creates a new export based on the
given BlockExportOptions.

qmp_nbd_server_add() becomes a wrapper around qmp_block_export_add().

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200924152717.287415-5-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

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);
+}

block/export/meson.build

@@ -0,0 +1 @@
+block_ss.add(files('export.c'))

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}

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,

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

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,

meson.build

@@ -970,6 +970,7 @@ subdir('dump')
 
 block_ss.add(files(
   'block.c',
+  'blockdev-nbd.c',
   'blockjob.c',
   'job.c',
   'qemu-io-cmds.c',
@@ -982,7 +983,6 @@ subdir('block')
 
 blockdev_ss.add(files(
   'blockdev.c',
-  'blockdev-nbd.c',
   'iothread.c',
   'job-qmp.c',
 ))

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;

qapi/block-export.json

@@ -172,3 +172,13 @@
   'data': {
       'nbd': 'BlockExportOptionsNbd'
    } }
+
+##
+# @block-export-add:
+#
+# Creates a new block export.
+#
+# Since: 5.2
+##
+{ 'command': 'block-export-add',
+  'data': 'BlockExportOptions', 'boxed': true }