[Qemu-devel] [PATCH 02/23] block: New BlockBackend

[Markus Armbruster <armbru@redhat.com>]

A block device consists of a frontend device model and a backend.

A block backend has a tree of block drivers doing the actual work.
The tree is managed by the block layer.

We currently use a single abstraction BlockDriverState both for tree
nodes and the backend as a whole.  Drawbacks:

* Its API includes both stuff that makes sense only at the block
  backend level (root of the tree) and stuff that's only for use
  within the block layer.  This makes the API bigger and more complex
  than necessary.  Moreover, it's not obvious which interfaces are
  meant for device models, and which really aren't.

* Since device models keep a reference to their backend, the backend
  object can't just be destroyed.  But for media change, we need to
  replace the tree.  Our solution is to make the BlockDriverState
  generic, with actual driver state in a separate object, pointed to
  by member opaque.  That lets us replace the tree by deinitializing
  and reinitializing its root.  This special need of the root makes
  the data structure awkward everywhere in the tree.

The general plan is to separate the APIs into "block backend", for use
by device models, monitor and whatever other code dealing with block
backends, and "block driver", for use by the block layer and whatever
other code (if any) dealing with trees and tree nodes.

Code dealing with block backends, device models in particular, should
become completely oblivious of BlockDriverState.  This should let us
clean up both APIs, and the tree data structures.

This commit is a first step.  It creates a minimal "block backend"
API: type BlockBackend and functions to create, destroy and find them.
BlockBackend objects are created and destroyed, but not yet used for
anything; that'll come shortly.

BlockBackend is reference-counted.  Its reference count never exceeds
one so far, but that's going to change.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 block/Makefile.objs            |   2 +-
 block/block-backend.c          | 110 +++++++++++++++++++++++++++++++++++++++++
 blockdev.c                     |  10 +++-
 hw/block/xen_disk.c            |  11 +++++
 include/qemu/typedefs.h        |   1 +
 include/sysemu/block-backend.h |  26 ++++++++++
 qemu-img.c                     |  46 +++++++++++++++++
 qemu-io.c                      |   8 +++
 qemu-nbd.c                     |   3 +-
 9 files changed, 214 insertions(+), 3 deletions(-)
 create mode 100644 block/block-backend.c
 create mode 100644 include/sysemu/block-backend.h

diff --git a/block/Makefile.objs b/block/Makefile.objs
index f45f939..a70140b 100644
--- a/block/Makefile.objs
+++ b/block/Makefile.objs
@@ -5,7 +5,7 @@ block-obj-y += qed-check.o
 block-obj-$(CONFIG_VHDX) += vhdx.o vhdx-endian.o vhdx-log.o
 block-obj-$(CONFIG_QUORUM) += quorum.o
 block-obj-y += parallels.o blkdebug.o blkverify.o
-block-obj-y += snapshot.o qapi.o
+block-obj-y += block-backend.o snapshot.o qapi.o
 block-obj-$(CONFIG_WIN32) += raw-win32.o win32-aio.o
 block-obj-$(CONFIG_POSIX) += raw-posix.o
 block-obj-$(CONFIG_LINUX_AIO) += linux-aio.o
diff --git a/block/block-backend.c b/block/block-backend.c
new file mode 100644
index 0000000..833f7d9
--- /dev/null
+++ b/block/block-backend.c
@@ -0,0 +1,110 @@
+/*
+ * QEMU Block backends
+ *
+ * Copyright (C) 2014 Red Hat, Inc.
+ *
+ * Authors:
+ *  Markus Armbruster <armbru@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 "sysemu/block-backend.h"
+#include "block/block_int.h"
+
+struct BlockBackend {
+    char *name;
+    int refcnt;
+    QTAILQ_ENTRY(BlockBackend) link; /* for blk_backends */
+};
+
+static QTAILQ_HEAD(, BlockBackend) blk_backends =
+    QTAILQ_HEAD_INITIALIZER(blk_backends);
+
+/**
+ * blk_new:
+ * @name: name, must not be %NULL or empty
+ * @errp: return location for an error to be set on failure, or %NULL
+ *
+ * Create a new BlockBackend, with a reference count of one.  Fail if
+ * @name already exists.
+ *
+ * Returns: the BlockBackend on success, %NULL on failure
+ */
+BlockBackend *blk_new(const char *name, Error **errp)
+{
+    BlockBackend *blk = g_new0(BlockBackend, 1);
+
+    assert(name && name[0]);
+    if (blk_by_name(name)) {
+        error_setg(errp, "Device with id '%s' already exists", name);
+        return NULL;
+    }
+    blk->name = g_strdup(name);
+    blk->refcnt = 1;
+    QTAILQ_INSERT_TAIL(&blk_backends, blk, link);
+    return blk;
+}
+
+static void blk_delete(BlockBackend *blk)
+{
+    assert(!blk->refcnt);
+    QTAILQ_REMOVE(&blk_backends, blk, link);
+    g_free(blk->name);
+    g_free(blk);
+}
+
+/**
+ * blk_ref:
+ *
+ * Increment @blk's reference count.
+ */
+void blk_ref(BlockBackend *blk)
+{
+    blk->refcnt++;
+}
+
+/**
+ * blk_unref:
+ *
+ * Decrement @blk's reference count.  If this drops it to zero,
+ * destroy @blk.
+ */
+void blk_unref(BlockBackend *blk)
+{
+    if (blk) {
+        g_assert(blk->refcnt > 0);
+        if (!--blk->refcnt) {
+            blk_delete(blk);
+        }
+    }
+}
+
+const char *blk_name(BlockBackend *blk)
+{
+    return blk->name;
+}
+
+BlockBackend *blk_by_name(const char *name)
+{
+    BlockBackend *blk;
+
+    QTAILQ_FOREACH(blk, &blk_backends, link) {
+        if (!strcmp(name, blk->name)) {
+            return blk;
+        }
+    }
+    return NULL;
+}
+
+/**
+ * blk_next:
+ *
+ * Returns: the first BlockBackend if @blk is null, else @blk's next
+ * sibling, which is %NULL for the last BlockBackend
+ */
+BlockBackend *blk_next(BlockBackend *blk)
+{
+    return blk ? QTAILQ_NEXT(blk, link) : QTAILQ_FIRST(&blk_backends);
+}
diff --git a/blockdev.c b/blockdev.c
index 9fbd888..86596bc 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -30,6 +30,7 @@
  * THE SOFTWARE.
  */
 
+#include "sysemu/block-backend.h"
 #include "sysemu/blockdev.h"
 #include "hw/block/block.h"
 #include "block/blockjob.h"
@@ -221,6 +222,7 @@ void drive_del(DriveInfo *dinfo)
     }
 
     bdrv_unref(dinfo->bdrv);
+    blk_unref(blk_by_name(dinfo->id));
     g_free(dinfo->id);
     QTAILQ_REMOVE(&drives, dinfo, next);
     g_free(dinfo->serial);
@@ -301,6 +303,7 @@ static DriveInfo *blockdev_init(const char *file, QDict *bs_opts,
     int ro = 0;
     int bdrv_flags = 0;
     int on_read_error, on_write_error;
+    BlockBackend *blk;
     DriveInfo *dinfo;
     ThrottleConfig cfg;
     int snapshot = 0;
@@ -456,6 +459,10 @@ static DriveInfo *blockdev_init(const char *file, QDict *bs_opts,
     }
 
     /* init */
+    blk = blk_new(qemu_opts_id(opts), errp);
+    if (!blk) {
+        goto early_err;
+    }
     dinfo = g_malloc0(sizeof(*dinfo));
     dinfo->id = g_strdup(qemu_opts_id(opts));
     dinfo->bdrv = bdrv_new_named(dinfo->id, &error);
@@ -525,6 +532,7 @@ err:
 bdrv_new_err:
     g_free(dinfo->id);
     g_free(dinfo);
+    blk_unref(blk);
 early_err:
     qemu_opts_del(opts);
 err_no_opts:
@@ -1770,7 +1778,7 @@ int do_drive_del(Monitor *mon, const QDict *qdict, QObject **ret_data)
      */
     if (bdrv_get_attached_dev(bs)) {
         bdrv_make_anon(bs);
-
+        blk_unref(blk_by_name(id));
         /* Further I/O must not pause the guest */
         bdrv_set_on_error(bs, BLOCKDEV_ON_ERROR_REPORT,
                           BLOCKDEV_ON_ERROR_REPORT);
diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
index 8bac7ff..730a021 100644
--- a/hw/block/xen_disk.c
+++ b/hw/block/xen_disk.c
@@ -39,6 +39,7 @@
 #include "hw/xen/xen_backend.h"
 #include "xen_blkif.h"
 #include "sysemu/blockdev.h"
+#include "sysemu/block-backend.h"
 
 /* ------------------------------------------------------------- */
 
@@ -852,12 +853,18 @@ static int blk_connect(struct XenDevice *xendev)
     blkdev->dinfo = drive_get(IF_XEN, 0, index);
     if (!blkdev->dinfo) {
         Error *local_err = NULL;
+        BlockBackend *blk;
         BlockDriver *drv;
 
         /* setup via xenbus -> create new block driver instance */
         xen_be_printf(&blkdev->xendev, 2, "create new bdrv (xenbus setup)\n");
+        blk = blk_new(blkdev->dev, NULL);
+        if (!blk) {
+            return -1;
+        }
         blkdev->bs = bdrv_new_named(blkdev->dev, NULL);
         if (!blkdev->bs) {
+            blk_unref(blk);
             return -1;
         }
 
@@ -868,6 +875,7 @@ static int blk_connect(struct XenDevice *xendev)
                           error_get_pretty(local_err));
             error_free(local_err);
             bdrv_unref(blkdev->bs);
+            blk_unref(blk);
             blkdev->bs = NULL;
             return -1;
         }
@@ -983,6 +991,9 @@ static void blk_disconnect(struct XenDevice *xendev)
     if (blkdev->bs) {
         bdrv_detach_dev(blkdev->bs, blkdev);
         bdrv_unref(blkdev->bs);
+        if (!blkdev->dinfo) {
+            blk_unref(blk_by_name(blkdev->dev));
+        }
         blkdev->bs = NULL;
     }
     xen_be_unbind_evtchn(&blkdev->xendev);
diff --git a/include/qemu/typedefs.h b/include/qemu/typedefs.h
index 5f20b0e..198da2e 100644
--- a/include/qemu/typedefs.h
+++ b/include/qemu/typedefs.h
@@ -35,6 +35,7 @@ typedef struct MachineClass MachineClass;
 typedef struct NICInfo NICInfo;
 typedef struct HCIInfo HCIInfo;
 typedef struct AudioState AudioState;
+typedef struct BlockBackend BlockBackend;
 typedef struct BlockDriverState BlockDriverState;
 typedef struct DriveInfo DriveInfo;
 typedef struct DisplayState DisplayState;
diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h
new file mode 100644
index 0000000..3f8371c
--- /dev/null
+++ b/include/sysemu/block-backend.h
@@ -0,0 +1,26 @@
+/*
+ * QEMU Block backends
+ *
+ * Copyright (C) 2014 Red Hat, Inc.
+ *
+ * Authors:
+ *  Markus Armbruster <armbru@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_BACKEND_H
+#define BLOCK_BACKEND_H
+
+#include "qemu/typedefs.h"
+#include "qapi/error.h"
+
+BlockBackend *blk_new(const char *name, Error **errp);
+void blk_ref(BlockBackend *blk);
+void blk_unref(BlockBackend *blk);
+const char *blk_name(BlockBackend *blk);
+BlockBackend *blk_by_name(const char *name);
+BlockBackend *blk_next(BlockBackend *blk);
+
+#endif
diff --git a/qemu-img.c b/qemu-img.c
index 4490a22..bad3f64 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -29,6 +29,7 @@
 #include "qemu/error-report.h"
 #include "qemu/osdep.h"
 #include "sysemu/sysemu.h"
+#include "sysemu/block-backend.h"
 #include "block/block_int.h"
 #include "block/qapi.h"
 #include <getopt.h>
@@ -575,6 +576,7 @@ static int img_check(int argc, char **argv)
     int c, ret;
     OutputFormat output_format = OFORMAT_HUMAN;
     const char *filename, *fmt, *output, *cache;
+    BlockBackend *blk;
     BlockDriverState *bs;
     int fix = 0;
     int flags = BDRV_O_FLAGS | BDRV_O_CHECK;
@@ -649,6 +651,7 @@ static int img_check(int argc, char **argv)
         return 1;
     }
 
+    blk = blk_new("image", &error_abort);
     bs = bdrv_new_open("image", filename, fmt, flags, true, quiet);
     if (!bs) {
         return 1;
@@ -710,6 +713,7 @@ static int img_check(int argc, char **argv)
 fail:
     qapi_free_ImageCheck(check);
     bdrv_unref(bs);
+    blk_unref(blk);
 
     return ret;
 }
@@ -718,6 +722,7 @@ static int img_commit(int argc, char **argv)
 {
     int c, ret, flags;
     const char *filename, *fmt, *cache;
+    BlockBackend *blk;
     BlockDriverState *bs;
     bool quiet = false;
 
@@ -756,6 +761,7 @@ static int img_commit(int argc, char **argv)
         return 1;
     }
 
+    blk = blk_new("image", &error_abort);
     bs = bdrv_new_open("image", filename, fmt, flags, true, quiet);
     if (!bs) {
         return 1;
@@ -780,6 +786,7 @@ static int img_commit(int argc, char **argv)
     }
 
     bdrv_unref(bs);
+    blk_unref(blk);
     if (ret) {
         return 1;
     }
@@ -942,6 +949,7 @@ static int check_empty_sectors(BlockDriverState *bs, int64_t sect_num,
 static int img_compare(int argc, char **argv)
 {
     const char *fmt1 = NULL, *fmt2 = NULL, *cache, *filename1, *filename2;
+    BlockBackend *blk1, *blk2;
     BlockDriverState *bs1, *bs2;
     int64_t total_sectors1, total_sectors2;
     uint8_t *buf1 = NULL, *buf2 = NULL;
@@ -1011,6 +1019,7 @@ static int img_compare(int argc, char **argv)
         goto out3;
     }
 
+    blk1 = blk_new("image 1", &error_abort);
     bs1 = bdrv_new_open("image 1", filename1, fmt1, flags, true, quiet);
     if (!bs1) {
         error_report("Can't open file %s", filename1);
@@ -1018,6 +1027,7 @@ static int img_compare(int argc, char **argv)
         goto out3;
     }
 
+    blk2 = blk_new("image 2", &error_abort);
     bs2 = bdrv_new_open("image 2", filename2, fmt2, flags, true, quiet);
     if (!bs2) {
         error_report("Can't open file %s", filename2);
@@ -1184,10 +1194,12 @@ static int img_compare(int argc, char **argv)
 
 out:
     bdrv_unref(bs2);
+    blk_unref(blk2);
     qemu_vfree(buf1);
     qemu_vfree(buf2);
 out2:
     bdrv_unref(bs1);
+    blk_unref(blk1);
 out3:
     qemu_progress_end();
     return ret;
@@ -1200,6 +1212,7 @@ static int img_convert(int argc, char **argv)
     int progress = 0, flags, src_flags;
     const char *fmt, *out_fmt, *cache, *src_cache, *out_baseimg, *out_filename;
     BlockDriver *drv, *proto_drv;
+    BlockBackend **blk = NULL, *out_blk = NULL;
     BlockDriverState **bs = NULL, *out_bs = NULL;
     int64_t total_sectors, nb_sectors, sector_num, bs_offset;
     int64_t *bs_sectors = NULL;
@@ -1354,6 +1367,7 @@ static int img_convert(int argc, char **argv)
 
     qemu_progress_print(0, 100);
 
+    blk = g_new0(BlockBackend *, bs_n);
     bs = g_new0(BlockDriverState *, bs_n);
     bs_sectors = g_new(int64_t, bs_n);
 
@@ -1361,6 +1375,7 @@ static int img_convert(int argc, char **argv)
     for (bs_i = 0; bs_i < bs_n; bs_i++) {
         char *id = bs_n > 1 ? g_strdup_printf("source %d", bs_i)
                             : g_strdup("source");
+        blk[bs_i] = blk_new(id, &error_abort);
         bs[bs_i] = bdrv_new_open(id, argv[optind + bs_i], fmt, src_flags,
                                  true, quiet);
         g_free(id);
@@ -1486,6 +1501,7 @@ static int img_convert(int argc, char **argv)
         goto out;
     }
 
+    out_blk = blk_new("target", &error_abort);
     out_bs = bdrv_new_open("target", out_filename, out_fmt, flags, true, quiet);
     if (!out_bs) {
         ret = -1;
@@ -1742,6 +1758,7 @@ out:
     if (out_bs) {
         bdrv_unref(out_bs);
     }
+    blk_unref(out_blk);
     if (bs) {
         for (bs_i = 0; bs_i < bs_n; bs_i++) {
             if (bs[bs_i]) {
@@ -1750,6 +1767,12 @@ out:
         }
         g_free(bs);
     }
+    if (blk) {
+        for (bs_i = 0; bs_i < bs_n; bs_i++) {
+            blk_unref(blk[bs_i]);
+        }
+        g_free(blk);
+    }
     g_free(bs_sectors);
 fail_getopt:
     g_free(options);
@@ -1858,6 +1881,7 @@ static ImageInfoList *collect_image_info_list(const char *filename,
     filenames = g_hash_table_new_full(g_str_hash, str_equal_func, NULL, NULL);
 
     while (filename) {
+        BlockBackend *blk;
         BlockDriverState *bs;
         ImageInfo *info;
         ImageInfoList *elem;
@@ -1869,6 +1893,7 @@ static ImageInfoList *collect_image_info_list(const char *filename,
         }
         g_hash_table_insert(filenames, (gpointer)filename, NULL);
 
+        blk = blk_new("image", &error_abort);
         bs = bdrv_new_open("image", filename, fmt,
                            BDRV_O_FLAGS | BDRV_O_NO_BACKING, false, false);
         if (!bs) {
@@ -1880,6 +1905,7 @@ static ImageInfoList *collect_image_info_list(const char *filename,
             error_report("%s", error_get_pretty(err));
             error_free(err);
             bdrv_unref(bs);
+            blk_unref(blk);
             goto err;
         }
 
@@ -1889,6 +1915,7 @@ static ImageInfoList *collect_image_info_list(const char *filename,
         last = &elem->next;
 
         bdrv_unref(bs);
+        blk_unref(blk);
 
         filename = fmt = NULL;
         if (chain) {
@@ -2082,6 +2109,7 @@ static int img_map(int argc, char **argv)
 {
     int c;
     OutputFormat output_format = OFORMAT_HUMAN;
+    BlockBackend *blk;
     BlockDriverState *bs;
     const char *filename, *fmt, *output;
     int64_t length;
@@ -2130,6 +2158,7 @@ static int img_map(int argc, char **argv)
         return 1;
     }
 
+    blk = blk_new("image", &error_abort);
     bs = bdrv_new_open("image", filename, fmt, BDRV_O_FLAGS, true, false);
     if (!bs) {
         return 1;
@@ -2175,6 +2204,7 @@ static int img_map(int argc, char **argv)
 
 out:
     bdrv_unref(bs);
+    blk_unref(blk);
     return ret < 0;
 }
 
@@ -2185,6 +2215,7 @@ out:
 
 static int img_snapshot(int argc, char **argv)
 {
+    BlockBackend *blk;
     BlockDriverState *bs;
     QEMUSnapshotInfo sn;
     char *filename, *snapshot_name = NULL;
@@ -2250,6 +2281,7 @@ static int img_snapshot(int argc, char **argv)
     filename = argv[optind++];
 
     /* Open the image */
+    blk = blk_new("image", &error_abort);
     bs = bdrv_new_open("image", filename, NULL, bdrv_oflags, true, quiet);
     if (!bs) {
         return 1;
@@ -2297,6 +2329,7 @@ static int img_snapshot(int argc, char **argv)
 
     /* Cleanup */
     bdrv_unref(bs);
+    blk_unref(blk);
     if (ret) {
         return 1;
     }
@@ -2305,6 +2338,7 @@ static int img_snapshot(int argc, char **argv)
 
 static int img_rebase(int argc, char **argv)
 {
+    BlockBackend *blk = NULL, *blk_old_backing = NULL, *blk_new_backing = NULL;
     BlockDriverState *bs = NULL, *bs_old_backing = NULL, *bs_new_backing = NULL;
     BlockDriver *old_backing_drv, *new_backing_drv;
     char *filename;
@@ -2393,6 +2427,7 @@ static int img_rebase(int argc, char **argv)
      * Ignore the old backing file for unsafe rebase in case we want to correct
      * the reference to a renamed or moved backing file.
      */
+    blk = blk_new("image", &error_abort);
     bs = bdrv_new_open("image", filename, fmt, flags, true, quiet);
     if (!bs) {
         ret = -1;
@@ -2425,6 +2460,7 @@ static int img_rebase(int argc, char **argv)
     if (!unsafe) {
         char backing_name[1024];
 
+        blk_old_backing = blk_new("old_backing", &error_abort);
         bs_old_backing = bdrv_new_named("old_backing", &error_abort);
         bdrv_get_backing_filename(bs, backing_name, sizeof(backing_name));
         ret = bdrv_open(&bs_old_backing, backing_name, NULL, NULL, src_flags,
@@ -2436,6 +2472,7 @@ static int img_rebase(int argc, char **argv)
             goto out;
         }
         if (out_baseimg[0]) {
+            blk_new_backing = blk_new("new_backing", &error_abort);
             bs_new_backing = bdrv_new_named("new_backing", &error_abort);
             ret = bdrv_open(&bs_new_backing, out_baseimg, NULL, NULL, src_flags,
                             new_backing_drv, &local_err);
@@ -2614,12 +2651,15 @@ out:
         if (bs_old_backing != NULL) {
             bdrv_unref(bs_old_backing);
         }
+        blk_unref(blk_old_backing);
         if (bs_new_backing != NULL) {
             bdrv_unref(bs_new_backing);
         }
+        blk_unref(blk_new_backing);
     }
 
     bdrv_unref(bs);
+    blk_unref(blk);
     if (ret) {
         return 1;
     }
@@ -2632,6 +2672,7 @@ static int img_resize(int argc, char **argv)
     const char *filename, *fmt, *size;
     int64_t n, total_size;
     bool quiet = false;
+    BlockBackend *blk = NULL;
     BlockDriverState *bs = NULL;
     QemuOpts *param;
     static QemuOptsList resize_options = {
@@ -2708,6 +2749,7 @@ static int img_resize(int argc, char **argv)
     n = qemu_opt_get_size(param, BLOCK_OPT_SIZE, 0);
     qemu_opts_del(param);
 
+    blk = blk_new("image", &error_abort);
     bs = bdrv_new_open("image", filename, fmt, BDRV_O_FLAGS | BDRV_O_RDWR,
                        true, quiet);
     if (!bs) {
@@ -2745,6 +2787,7 @@ out:
     if (bs) {
         bdrv_unref(bs);
     }
+    blk_unref(blk);
     if (ret) {
         return 1;
     }
@@ -2760,6 +2803,7 @@ static int img_amend(int argc, char **argv)
     const char *fmt = NULL, *filename, *cache;
     int flags;
     bool quiet = false;
+    BlockBackend *blk = NULL;
     BlockDriverState *bs = NULL;
 
     cache = BDRV_DEFAULT_CACHE;
@@ -2823,6 +2867,7 @@ static int img_amend(int argc, char **argv)
         goto out;
     }
 
+    blk = blk_new("image", &error_abort);
     bs = bdrv_new_open("image", filename, fmt, flags, true, quiet);
     if (!bs) {
         error_report("Could not open image '%s'", filename);
@@ -2856,6 +2901,7 @@ out:
     if (bs) {
         bdrv_unref(bs);
     }
+    blk_unref(blk);
     qemu_opts_del(opts);
     qemu_opts_free(create_opts);
     g_free(options);
diff --git a/qemu-io.c b/qemu-io.c
index 44c2e1c..45e5494 100644
--- a/qemu-io.c
+++ b/qemu-io.c
@@ -19,6 +19,7 @@
 #include "qemu/option.h"
 #include "qemu/config-file.h"
 #include "qemu/readline.h"
+#include "sysemu/block-backend.h"
 #include "block/block_int.h"
 #include "trace/control.h"
 
@@ -26,6 +27,7 @@
 
 static char *progname;
 
+static BlockBackend *qemuio_blk;
 static BlockDriverState *qemuio_bs;
 
 /* qemu-io commands passed using -c */
@@ -37,7 +39,9 @@ static ReadLineState *readline_state;
 static int close_f(BlockDriverState *bs, int argc, char **argv)
 {
     bdrv_unref(bs);
+    blk_unref(qemuio_blk);
     qemuio_bs = NULL;
+    qemuio_blk = NULL;
     return 0;
 }
 
@@ -58,6 +62,7 @@ static int openfile(char *name, int flags, int growable, QDict *opts)
         return 1;
     }
 
+    qemuio_blk = blk_new("hda", &error_abort);
     qemuio_bs = bdrv_new_named("hda", &error_abort);
 
     if (growable) {
@@ -70,7 +75,9 @@ static int openfile(char *name, int flags, int growable, QDict *opts)
                 error_get_pretty(local_err));
         error_free(local_err);
         bdrv_unref(qemuio_bs);
+        blk_unref(qemuio_blk);
         qemuio_bs = NULL;
+        qemuio_blk = NULL;
         return 1;
     }
 
@@ -479,6 +486,7 @@ int main(int argc, char **argv)
     if (qemuio_bs) {
         bdrv_unref(qemuio_bs);
     }
+    blk_unref(qemuio_blk);
     g_free(readline_state);
     return 0;
 }
diff --git a/qemu-nbd.c b/qemu-nbd.c
index a56ebfc..94b9b49 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -17,7 +17,7 @@
  */
 
 #include "qemu-common.h"
-#include "block/block.h"
+#include "sysemu/block-backend.h"
 #include "block/block_int.h"
 #include "block/nbd.h"
 #include "qemu/main-loop.h"
@@ -687,6 +687,7 @@ int main(int argc, char **argv)
         drv = NULL;
     }
 
+    blk_new("hda", &error_abort);
     bs = bdrv_new_named("hda", &error_abort);
 
     srcpath = argv[optind];
-- 
1.9.3