[Qemu-devel] [RFC V2 0/3] Giving names to BlockDriverState graph nodes

[Qemu-devel] [RFC V2 0/3] Giving names to BlockDriverState graph nodes

[Benoît Canet]

This series fix the issues of V1 and add the skeletton of a new QMP command
useful to communicate a bs graph to libvirt.
The minimum is exposed to the management to avoid binding it too much with QEMU.

Tell me if you think it's worth implementing.

Best regards

Benoît

v2:
   s/give/gives/ [Eric]
   s/see/sees/   [Eric]
   prevent duplicate node_name [Eric]
   drop "undefined" and use "" [Eric, Kevin, Jeff]
   remove from graph list on bdrv_make_anon [Jeff]
   comment the two chains [Fam]
   Add new command stub to retrieve the graph from libvirt [Benoît]

Benoît Canet (3):
  block: Add bs->node_name to hold the name of a bs node of the bs
    graph.
  block: Allow the user to define "node-name" option.
  qapi: Add skeletton of command to query a drive bs graph.

 block.c                   | 88 +++++++++++++++++++++++++++++++++++++----------
 block/blkverify.c         |  2 +-
 block/iscsi.c             |  2 +-
 block/vmdk.c              |  2 +-
 block/vvfat.c             |  4 +--
 blockdev.c                | 16 ++++++---
 hw/block/xen_disk.c       |  2 +-
 include/block/block.h     |  3 +-
 include/block/block_int.h |  9 ++++-
 qapi-schema.json          | 32 +++++++++++++++++
 qemu-img.c                |  6 ++--
 qemu-io.c                 |  2 +-
 qemu-nbd.c                |  2 +-
 13 files changed, 134 insertions(+), 36 deletions(-)

-- 
1.8.3.2

[Qemu-devel] [RFC V2 1/3] block: Add bs->node_name to hold the name of a bs node of the bs graph.

[Benoît Canet]

Add the minimum of code to prepare the followings patches.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
---
 block.c                   | 72 ++++++++++++++++++++++++++++++++++-------------
 block/blkverify.c         |  2 +-
 block/iscsi.c             |  2 +-
 block/vmdk.c              |  2 +-
 block/vvfat.c             |  4 +--
 blockdev.c                |  8 +++---
 hw/block/xen_disk.c       |  2 +-
 include/block/block.h     |  3 +-
 include/block/block_int.h |  9 +++++-
 qemu-img.c                |  6 ++--
 qemu-io.c                 |  2 +-
 qemu-nbd.c                |  2 +-
 12 files changed, 78 insertions(+), 36 deletions(-)

diff --git a/block.c b/block.c
index fd05a80..c397ee9 100644
--- a/block.c
+++ b/block.c
@@ -89,6 +89,9 @@ static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs,
 static QTAILQ_HEAD(, BlockDriverState) bdrv_states =
     QTAILQ_HEAD_INITIALIZER(bdrv_states);
 
+static QTAILQ_HEAD(, BlockDriverState) graph_bdrv_states =
+    QTAILQ_HEAD_INITIALIZER(graph_bdrv_states);
+
 static QLIST_HEAD(, BlockDriver) bdrv_drivers =
     QLIST_HEAD_INITIALIZER(bdrv_drivers);
 
@@ -318,14 +321,20 @@ void bdrv_register(BlockDriver *bdrv)
 }
 
 /* create a new block device (by default it is empty) */
-BlockDriverState *bdrv_new(const char *device_name)
+BlockDriverState *bdrv_new(const char *device_name, const char *node_name)
 {
     BlockDriverState *bs;
 
+    assert(node_name);
+
     bs = g_malloc0(sizeof(BlockDriverState));
     pstrcpy(bs->device_name, sizeof(bs->device_name), device_name);
     if (device_name[0] != '\0') {
-        QTAILQ_INSERT_TAIL(&bdrv_states, bs, list);
+        QTAILQ_INSERT_TAIL(&bdrv_states, bs, device_list);
+    }
+    pstrcpy(bs->node_name, sizeof(bs->node_name), node_name);
+    if (node_name[0] != '\0') {
+        QTAILQ_INSERT_TAIL(&graph_bdrv_states, bs, node_list);
     }
     bdrv_iostatus_disable(bs);
     notifier_list_init(&bs->close_notifiers);
@@ -870,7 +879,7 @@ int bdrv_file_open(BlockDriverState **pbs, const char *filename,
         options = qdict_new();
     }
 
-    bs = bdrv_new("");
+    bs = bdrv_new("", "");
     bs->options = options;
     options = qdict_clone_shallow(options);
 
@@ -992,7 +1001,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp)
                                        sizeof(backing_filename));
     }
 
-    bs->backing_hd = bdrv_new("");
+    bs->backing_hd = bdrv_new("", "");
 
     if (bs->backing_format[0] != '\0') {
         back_drv = bdrv_find_format(bs->backing_format);
@@ -1062,7 +1071,7 @@ int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
            instead of opening 'filename' directly */
 
         /* if there is a backing file, use it */
-        bs1 = bdrv_new("");
+        bs1 = bdrv_new("", "");
         ret = bdrv_open(bs1, filename, NULL, 0, drv, &local_err);
         if (ret < 0) {
             bdrv_unref(bs1);
@@ -1495,7 +1504,7 @@ void bdrv_close_all(void)
 {
     BlockDriverState *bs;
 
-    QTAILQ_FOREACH(bs, &bdrv_states, list) {
+    QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
         bdrv_close(bs);
     }
 }
@@ -1524,7 +1533,7 @@ static bool bdrv_requests_pending(BlockDriverState *bs)
 static bool bdrv_requests_pending_all(void)
 {
     BlockDriverState *bs;
-    QTAILQ_FOREACH(bs, &bdrv_states, list) {
+    QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
         if (bdrv_requests_pending(bs)) {
             return true;
         }
@@ -1554,7 +1563,7 @@ void bdrv_drain_all(void)
         /* FIXME: We do not have timer support here, so this is effectively
          * a busy wait.
          */
-        QTAILQ_FOREACH(bs, &bdrv_states, list) {
+        QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
             if (bdrv_start_throttled_reqs(bs)) {
                 busy = true;
             }
@@ -1565,14 +1574,18 @@ void bdrv_drain_all(void)
     }
 }
 
-/* make a BlockDriverState anonymous by removing from bdrv_state list.
+/* make a BlockDriverState anonymous by removing from bdrv_state and
+ * graph_bdrv_state list.
    Also, NULL terminate the device_name to prevent double remove */
 void bdrv_make_anon(BlockDriverState *bs)
 {
     if (bs->device_name[0] != '\0') {
-        QTAILQ_REMOVE(&bdrv_states, bs, list);
+        QTAILQ_REMOVE(&bdrv_states, bs, device_list);
     }
     bs->device_name[0] = '\0';
+    if (bs->node_name[0] != '\0') {
+        QTAILQ_REMOVE(&graph_bdrv_states, bs, node_list);
+    }
 }
 
 static void bdrv_rebind(BlockDriverState *bs)
@@ -1626,7 +1639,12 @@ static void bdrv_move_feature_fields(BlockDriverState *bs_dest,
     /* keep the same entry in bdrv_states */
     pstrcpy(bs_dest->device_name, sizeof(bs_dest->device_name),
             bs_src->device_name);
-    bs_dest->list = bs_src->list;
+    bs_dest->device_list = bs_src->device_list;
+
+    /* keep the same entry in graph_bdrv_states */
+    pstrcpy(bs_dest->node_name, sizeof(bs_dest->node_name),
+            bs_src->node_name);
+    bs_dest->node_list   = bs_src->node_list;
 }
 
 /*
@@ -1950,7 +1968,7 @@ int bdrv_commit_all(void)
 {
     BlockDriverState *bs;
 
-    QTAILQ_FOREACH(bs, &bdrv_states, list) {
+    QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
         if (bs->drv && bs->backing_hd) {
             int ret = bdrv_commit(bs);
             if (ret < 0) {
@@ -3017,11 +3035,12 @@ void bdrv_iterate_format(void (*it)(void *opaque, const char *name),
     }
 }
 
+/* This function is to find block backend bs */
 BlockDriverState *bdrv_find(const char *name)
 {
     BlockDriverState *bs;
 
-    QTAILQ_FOREACH(bs, &bdrv_states, list) {
+    QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
         if (!strcmp(name, bs->device_name)) {
             return bs;
         }
@@ -3029,19 +3048,34 @@ BlockDriverState *bdrv_find(const char *name)
     return NULL;
 }
 
+/* This function is to find a node in the bs graph */
+BlockDriverState *bdrv_find_node(const char *node_name)
+{
+    BlockDriverState *bs;
+
+    assert(node_name);
+
+    QTAILQ_FOREACH(bs, &graph_bdrv_states, node_list) {
+        if (!strcmp(node_name, bs->node_name)) {
+            return bs;
+        }
+    }
+    return NULL;
+}
+
 BlockDriverState *bdrv_next(BlockDriverState *bs)
 {
     if (!bs) {
         return QTAILQ_FIRST(&bdrv_states);
     }
-    return QTAILQ_NEXT(bs, list);
+    return QTAILQ_NEXT(bs, device_list);
 }
 
 void bdrv_iterate(void (*it)(void *opaque, BlockDriverState *bs), void *opaque)
 {
     BlockDriverState *bs;
 
-    QTAILQ_FOREACH(bs, &bdrv_states, list) {
+    QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
         it(opaque, bs);
     }
 }
@@ -3061,7 +3095,7 @@ int bdrv_flush_all(void)
     BlockDriverState *bs;
     int result = 0;
 
-    QTAILQ_FOREACH(bs, &bdrv_states, list) {
+    QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
         int ret = bdrv_flush(bs);
         if (ret < 0 && !result) {
             result = ret;
@@ -4127,7 +4161,7 @@ void bdrv_invalidate_cache_all(void)
 {
     BlockDriverState *bs;
 
-    QTAILQ_FOREACH(bs, &bdrv_states, list) {
+    QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
         bdrv_invalidate_cache(bs);
     }
 }
@@ -4136,7 +4170,7 @@ void bdrv_clear_incoming_migration_all(void)
 {
     BlockDriverState *bs;
 
-    QTAILQ_FOREACH(bs, &bdrv_states, list) {
+    QTAILQ_FOREACH(bs, &bdrv_states, device_list) {
         bs->open_flags = bs->open_flags & ~(BDRV_O_INCOMING);
     }
 }
@@ -4582,7 +4616,7 @@ void bdrv_img_create(const char *filename, const char *fmt,
             back_flags =
                 flags & ~(BDRV_O_RDWR | BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING);
 
-            bs = bdrv_new("");
+            bs = bdrv_new("", "");
 
             ret = bdrv_open(bs, backing_file->value.s, NULL, back_flags,
                             backing_drv, &local_err);
diff --git a/block/blkverify.c b/block/blkverify.c
index 55819a0..e755e4e 100644
--- a/block/blkverify.c
+++ b/block/blkverify.c
@@ -155,7 +155,7 @@ static int blkverify_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
-    s->test_file = bdrv_new("");
+    s->test_file = bdrv_new("", "");
     ret = bdrv_open(s->test_file, filename, NULL, flags, NULL, &local_err);
     if (ret < 0) {
         error_propagate(errp, local_err);
diff --git a/block/iscsi.c b/block/iscsi.c
index a2a961e..673b156 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -1461,7 +1461,7 @@ static int iscsi_create(const char *filename, QEMUOptionParameter *options,
     IscsiLun *iscsilun = NULL;
     QDict *bs_options;
 
-    bs = bdrv_new("");
+    bs = bdrv_new("", "");
 
     /* Read out options */
     while (options && options->name) {
diff --git a/block/vmdk.c b/block/vmdk.c
index 32ec8b77..e258db8 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -1672,7 +1672,7 @@ static int vmdk_create(const char *filename, QEMUOptionParameter *options,
         return -ENOTSUP;
     }
     if (backing_file) {
-        BlockDriverState *bs = bdrv_new("");
+        BlockDriverState *bs = bdrv_new("", "");
         ret = bdrv_open(bs, backing_file, NULL, 0, NULL, errp);
         if (ret != 0) {
             bdrv_unref(bs);
diff --git a/block/vvfat.c b/block/vvfat.c
index 3ddaa0b..f973c08 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -2935,7 +2935,7 @@ static int enable_write_target(BDRVVVFATState *s)
         goto err;
     }
 
-    s->qcow = bdrv_new("");
+    s->qcow = bdrv_new("", "");
 
     ret = bdrv_open(s->qcow, s->qcow_filename, NULL,
             BDRV_O_RDWR | BDRV_O_CACHE_WB | BDRV_O_NO_FLUSH, bdrv_qcow,
@@ -2951,7 +2951,7 @@ static int enable_write_target(BDRVVVFATState *s)
     unlink(s->qcow_filename);
 #endif
 
-    s->bs->backing_hd = bdrv_new("");
+    s->bs->backing_hd = bdrv_new("", "");
     s->bs->backing_hd->drv = &vvfat_write_target;
     s->bs->backing_hd->opaque = g_malloc(sizeof(void*));
     *(void**)s->bs->backing_hd->opaque = s;
diff --git a/blockdev.c b/blockdev.c
index b260477..911ee7e 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -469,7 +469,7 @@ static DriveInfo *blockdev_init(QDict *bs_opts,
     /* init */
     dinfo = g_malloc0(sizeof(*dinfo));
     dinfo->id = g_strdup(qemu_opts_id(opts));
-    dinfo->bdrv = bdrv_new(dinfo->id);
+    dinfo->bdrv = bdrv_new(dinfo->id, "");
     dinfo->bdrv->open_flags = snapshot ? BDRV_O_SNAPSHOT : 0;
     dinfo->bdrv->read_only = ro;
     dinfo->type = type;
@@ -1254,7 +1254,7 @@ static void external_snapshot_prepare(BlkTransactionState *common,
     }
 
     /* We will manually add the backing_hd field to the bs later */
-    state->new_bs = bdrv_new("");
+    state->new_bs = bdrv_new("", "");
     /* TODO Inherit bs->options or only take explicit options with an
      * extended QMP command? */
     ret = bdrv_open(state->new_bs, new_image_file, NULL,
@@ -1921,7 +1921,7 @@ void qmp_drive_backup(const char *device, const char *target,
         return;
     }
 
-    target_bs = bdrv_new("");
+    target_bs = bdrv_new("", "");
     ret = bdrv_open(target_bs, target, NULL, flags, drv, &local_err);
     if (ret < 0) {
         bdrv_unref(target_bs);
@@ -2055,7 +2055,7 @@ void qmp_drive_mirror(const char *device, const char *target,
     /* Mirroring takes care of copy-on-write using the source's backing
      * file.
      */
-    target_bs = bdrv_new("");
+    target_bs = bdrv_new("", "");
     ret = bdrv_open(target_bs, target, NULL, flags | BDRV_O_NO_BACKING, drv,
                     &local_err);
     if (ret < 0) {
diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
index 098f6c6..e8a45d1 100644
--- a/hw/block/xen_disk.c
+++ b/hw/block/xen_disk.c
@@ -808,7 +808,7 @@ static int blk_connect(struct XenDevice *xendev)
     if (!blkdev->dinfo) {
         /* setup via xenbus -> create new block driver instance */
         xen_be_printf(&blkdev->xendev, 2, "create new bdrv (xenbus setup)\n");
-        blkdev->bs = bdrv_new(blkdev->dev);
+        blkdev->bs = bdrv_new(blkdev->dev, "");
         if (blkdev->bs) {
             Error *local_err = NULL;
             BlockDriver *drv = bdrv_find_whitelisted_format(blkdev->fileproto,
diff --git a/include/block/block.h b/include/block/block.h
index 3560deb..2d27bd9 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -149,7 +149,7 @@ int bdrv_create(BlockDriver *drv, const char* filename,
     QEMUOptionParameter *options, Error **errp);
 int bdrv_create_file(const char* filename, QEMUOptionParameter *options,
                      Error **errp);
-BlockDriverState *bdrv_new(const char *device_name);
+BlockDriverState *bdrv_new(const char *device_name, const char *node_name);
 void bdrv_make_anon(BlockDriverState *bs);
 void bdrv_swap(BlockDriverState *bs_new, BlockDriverState *bs_old);
 void bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top);
@@ -339,6 +339,7 @@ void bdrv_lock_medium(BlockDriverState *bs, bool locked);
 void bdrv_eject(BlockDriverState *bs, bool eject_flag);
 const char *bdrv_get_format_name(BlockDriverState *bs);
 BlockDriverState *bdrv_find(const char *name);
+BlockDriverState *bdrv_find_node(const char *node_name);
 BlockDriverState *bdrv_next(BlockDriverState *bs);
 void bdrv_iterate(void (*it)(void *opaque, BlockDriverState *bs),
                   void *opaque);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index a48731d..84d8db5 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -297,11 +297,18 @@ struct BlockDriverState {
     BlockdevOnError on_read_error, on_write_error;
     bool iostatus_enabled;
     BlockDeviceIoStatus iostatus;
+
+    /* the following member gives a name to every node on the bs graph. */
+    char node_name[32];
+    /* element of the list of named nodes building the graph */
+    QTAILQ_ENTRY(BlockDriverState) node_list;
+    /* Device name is the name associated with the "drive" the guest sees */
     char device_name[32];
+    /* element of the list of "drives" the guest sees */
+    QTAILQ_ENTRY(BlockDriverState) device_list;
     HBitmap *dirty_bitmap;
     int refcnt;
     int in_use; /* users other than guest access, eg. block migration */
-    QTAILQ_ENTRY(BlockDriverState) list;
 
     QLIST_HEAD(, BdrvTrackedRequest) tracked_requests;
 
diff --git a/qemu-img.c b/qemu-img.c
index 926f0a0..1803a59 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -269,7 +269,7 @@ static BlockDriverState *bdrv_new_open(const char *filename,
     Error *local_err = NULL;
     int ret;
 
-    bs = bdrv_new("image");
+    bs = bdrv_new("image", "");
 
     if (fmt) {
         drv = bdrv_find_format(fmt);
@@ -2225,7 +2225,7 @@ static int img_rebase(int argc, char **argv)
     } else {
         char backing_name[1024];
 
-        bs_old_backing = bdrv_new("old_backing");
+        bs_old_backing = bdrv_new("old_backing", "");
         bdrv_get_backing_filename(bs, backing_name, sizeof(backing_name));
         ret = bdrv_open(bs_old_backing, backing_name, NULL, BDRV_O_FLAGS,
                         old_backing_drv, &local_err);
@@ -2236,7 +2236,7 @@ static int img_rebase(int argc, char **argv)
             goto out;
         }
         if (out_baseimg[0]) {
-            bs_new_backing = bdrv_new("new_backing");
+            bs_new_backing = bdrv_new("new_backing", "");
             ret = bdrv_open(bs_new_backing, out_baseimg, NULL, BDRV_O_FLAGS,
                         new_backing_drv, &local_err);
             if (ret) {
diff --git a/qemu-io.c b/qemu-io.c
index 3b3340a..fb04c74 100644
--- a/qemu-io.c
+++ b/qemu-io.c
@@ -63,7 +63,7 @@ static int openfile(char *name, int flags, int growable, QDict *opts)
             return 1;
         }
     } else {
-        qemuio_bs = bdrv_new("hda");
+        qemuio_bs = bdrv_new("hda", "");
 
         if (bdrv_open(qemuio_bs, name, opts, flags, NULL, &local_err) < 0) {
             fprintf(stderr, "%s: can't open device %s: %s\n", progname, name,
diff --git a/qemu-nbd.c b/qemu-nbd.c
index c26c98e..245fecf 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -572,7 +572,7 @@ int main(int argc, char **argv)
         drv = NULL;
     }
 
-    bs = bdrv_new("hda");
+    bs = bdrv_new("hda", "");
     srcpath = argv[optind];
     ret = bdrv_open(bs, srcpath, NULL, flags, drv, &local_err);
     if (ret < 0) {
-- 
1.8.3.2

[Qemu-devel] [RFC V2 2/3] block: Allow the user to define "node-name" option.

[Benoît Canet]

Signed-off-by: Benoit Canet <benoit@irqsave.net>
---
 block.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/block.c b/block.c
index c397ee9..6690e3d 100644
--- a/block.c
+++ b/block.c
@@ -872,6 +872,7 @@ int bdrv_file_open(BlockDriverState **pbs, const char *filename,
     const char *drvname;
     bool allow_protocol_prefix = false;
     Error *local_err = NULL;
+    const char *node_name = NULL;
     int ret;
 
     /* NULL means an empty set of options */
@@ -879,7 +880,14 @@ int bdrv_file_open(BlockDriverState **pbs, const char *filename,
         options = qdict_new();
     }
 
-    bs = bdrv_new("", "");
+    node_name = qdict_get_try_str(options, "node-name");
+    if (node_name && bdrv_find_node(node_name)) {
+        error_setg(errp, "Duplicate node name");
+        return -EINVAL;
+    }
+    bs = bdrv_new("", node_name ? node_name : "");
+    qdict_del(options, "node-name");
+
     bs->options = options;
     options = qdict_clone_shallow(options);
 
@@ -979,6 +987,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp)
     int back_flags, ret;
     BlockDriver *back_drv = NULL;
     Error *local_err = NULL;
+    const char *node_name = NULL;
 
     if (bs->backing_hd != NULL) {
         QDECREF(options);
@@ -1001,7 +1010,14 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *options, Error **errp)
                                        sizeof(backing_filename));
     }
 
-    bs->backing_hd = bdrv_new("", "");
+    node_name = qdict_get_try_str(options, "node-name");
+    if (node_name && bdrv_find_node(node_name)) {
+        error_setg(errp, "Duplicate node name");
+        QDECREF(options);
+        return -EINVAL;
+    }
+    bs->backing_hd = bdrv_new("", node_name ? node_name : "");
+    qdict_del(options, "node-name");
 
     if (bs->backing_format[0] != '\0') {
         back_drv = bdrv_find_format(bs->backing_format);
-- 
1.8.3.2

[Qemu-devel] [RFC V2 3/3] qapi: Add skeletton of command to query a drive bs graph.

[Benoît Canet]

---
 blockdev.c       |  8 ++++++++
 qapi-schema.json | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/blockdev.c b/blockdev.c
index 911ee7e..bfaeda0 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1938,6 +1938,14 @@ void qmp_drive_backup(const char *device, const char *target,
     }
 }
 
+BlockGraphNode *qmp_query_drive_graph(const char *device, Error **errp)
+{
+    /* the implementation of this function would recurse through the
+     * BlockDriverState graph to build it's result
+     */
+    return NULL;
+}
+
 #define DEFAULT_MIRROR_BUF_SIZE   (10 << 20)
 
 void qmp_drive_mirror(const char *device, const char *target,
diff --git a/qapi-schema.json b/qapi-schema.json
index 60f3fd1..bca3d5a 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1983,6 +1983,38 @@
 { 'command': 'drive-backup', 'data': 'DriveBackup' }
 
 ##
+# @BlockGraphNode
+#
+# Information about a node of the block driver state graph
+#
+# @node-name: the name of the node in the graph
+#
+# @drv: the name of the block format used by this node as described in
+#       @BlockDeviceInfo.
+#
+# @children: a list of @BlockGraphNode being the children of this node
+#
+# Since 1.8
+##
+{ 'type': 'BlockGraphNode',
+  'data': { 'node-name': 'str', 'drv': 'str', 'children': ['BlockGraphNode'] } }
+
+##
+# @query-drive-graph
+#
+# Get the block driver states graph for a given drive
+#
+# @device: the name of the device to get the graph from
+#
+# Returns: the root @BlockGraphNode
+#
+# Since 1.8
+##
+{ 'command': 'query-drive-graph',
+  'data': { 'device': 'str' },
+  'returns': 'BlockGraphNode' }
+
+##
 # @drive-mirror
 #
 # Start mirroring a block device's writes to a new destination.
-- 
1.8.3.2