Merge remote-tracking branch 'remotes/stefanha/tags/block-pull-request' into staging

Block pull request

# gpg: Signature made Tue 01 Jul 2014 09:47:15 BST using RSA key ID 81AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>"
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>"

* remotes/stefanha/tags/block-pull-request: (23 commits)
  block: add backing-file option to block-stream
  block: extend block-commit to accept a string for the backing file
  block: add helper function to determine if a BDS is in a chain
  block: add QAPI command to allow live backing file change
  qapi: Change back sector-count to sectors-count in quorum QAPI events.
  block/cow: Avoid use of uninitialized cow_bs in error path
  block: simplify bdrv_find_base() and bdrv_find_overlay()
  block: make 'top' argument to block-commit optional
  iotests: Add more tests to quick group
  iotests: Add qemu tests to quick group
  iotests: Simplify qemu-iotests-quick.sh
  qemu-img create: add 'nocow' option
  virtio-blk: remove need for explicit x-data-plane=on option
  qdev: drop iothread property type
  virtio-blk: replace x-iothread with iothread link property
  virtio-blk: move qdev properties into virtio-blk.c
  virtio: fix virtio-blk child refcount in transports
  virtio-blk: drop virtio_blk_set_conf()
  virtio-blk: use aliases instead of duplicate qdev properties
  qdev: add qdev_alias_all_properties()
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

35 files changed, 569 insertions, 242 deletions

diff --git a/block.c b/block.c
index 6856c18aa8..f80e2b2b58 100644
--- a/block.c
+++ b/block.c
@@ -2508,32 +2508,23 @@ int bdrv_change_backing_file(BlockDriverState *bs,
  *
  * Returns NULL if bs is not found in active's image chain,
  * or if active == bs.
+ *
+ * Returns the bottommost base image if bs == NULL.
  */
 BlockDriverState *bdrv_find_overlay(BlockDriverState *active,
                                     BlockDriverState *bs)
 {
-    BlockDriverState *overlay = NULL;
-    BlockDriverState *intermediate;
-
-    assert(active != NULL);
-    assert(bs != NULL);
-
-    /* if bs is the same as active, then by definition it has no overlay
-     */
-    if (active == bs) {
-        return NULL;
+    while (active && bs != active->backing_hd) {
+        active = active->backing_hd;
     }
 
-    intermediate = active;
-    while (intermediate->backing_hd) {
-        if (intermediate->backing_hd == bs) {
-            overlay = intermediate;
-            break;
-        }
-        intermediate = intermediate->backing_hd;
-    }
+    return active;
+}
 
-    return overlay;
+/* Given a BDS, searches for the base layer. */
+BlockDriverState *bdrv_find_base(BlockDriverState *bs)
+{
+    return bdrv_find_overlay(bs, NULL);
 }
 
 typedef struct BlkIntermediateStates {
@@ -2564,12 +2555,15 @@ typedef struct BlkIntermediateStates {
  *
  * base <- active
  *
+ * If backing_file_str is non-NULL, it will be used when modifying top's
+ * overlay image metadata.
+ *
  * Error conditions:
  *  if active == top, that is considered an error
  *
  */
 int bdrv_drop_intermediate(BlockDriverState *active, BlockDriverState *top,
-                           BlockDriverState *base)
+                           BlockDriverState *base, const char *backing_file_str)
 {
     BlockDriverState *intermediate;
     BlockDriverState *base_bs = NULL;
@@ -2621,7 +2615,8 @@ int bdrv_drop_intermediate(BlockDriverState *active, BlockDriverState *top,
     }
 
     /* success - we can delete the intermediate states, and link top->base */
-    ret = bdrv_change_backing_file(new_top_bs, base_bs->filename,
+    backing_file_str = backing_file_str ? backing_file_str : base_bs->filename;
+    ret = bdrv_change_backing_file(new_top_bs, backing_file_str,
                                    base_bs->drv ? base_bs->drv->format_name : "");
     if (ret) {
         goto exit;
@@ -3783,6 +3778,17 @@ BlockDriverState *bdrv_lookup_bs(const char *device,
     return NULL;
 }
 
+/* If 'base' is in the same chain as 'top', return true. Otherwise,
+ * return false.  If either argument is NULL, return false. */
+bool bdrv_chain_contains(BlockDriverState *top, BlockDriverState *base)
+{
+    while (top && top != base) {
+        top = top->backing_hd;
+    }
+
+    return top != NULL;
+}
+
 BlockDriverState *bdrv_next(BlockDriverState *bs)
 {
     if (!bs) {
@@ -4326,22 +4332,6 @@ int bdrv_get_backing_file_depth(BlockDriverState *bs)
     return 1 + bdrv_get_backing_file_depth(bs->backing_hd);
 }
 
-BlockDriverState *bdrv_find_base(BlockDriverState *bs)
-{
-    BlockDriverState *curr_bs = NULL;
-
-    if (!bs) {
-        return NULL;
-    }
-
-    curr_bs = bs;
-
-    while (curr_bs->backing_hd) {
-        curr_bs = curr_bs->backing_hd;
-    }
-    return curr_bs;
-}
-
 /**************************************************************/
 /* async I/Os */
 
diff --git a/block/commit.c b/block/commit.c
index 5c09f4444e..91517d3512 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -37,6 +37,7 @@ typedef struct CommitBlockJob {
     BlockdevOnError on_error;
     int base_flags;
     int orig_overlay_flags;
+    char *backing_file_str;
 } CommitBlockJob;
 
 static int coroutine_fn commit_populate(BlockDriverState *bs,
@@ -141,7 +142,7 @@ wait:
 
     if (!block_job_is_cancelled(&s->common) && sector_num == end) {
         /* success */
-        ret = bdrv_drop_intermediate(active, top, base);
+        ret = bdrv_drop_intermediate(active, top, base, s->backing_file_str);
     }
 
 exit_free_buf:
@@ -158,7 +159,7 @@ exit_restore_reopen:
     if (overlay_bs && s->orig_overlay_flags != bdrv_get_flags(overlay_bs)) {
         bdrv_reopen(overlay_bs, s->orig_overlay_flags, NULL);
     }
-
+    g_free(s->backing_file_str);
     block_job_completed(&s->common, ret);
 }
 
@@ -182,7 +183,7 @@ static const BlockJobDriver commit_job_driver = {
 void commit_start(BlockDriverState *bs, BlockDriverState *base,
                   BlockDriverState *top, int64_t speed,
                   BlockdevOnError on_error, BlockDriverCompletionFunc *cb,
-                  void *opaque, Error **errp)
+                  void *opaque, const char *backing_file_str, Error **errp)
 {
     CommitBlockJob *s;
     BlockReopenQueue *reopen_queue = NULL;
@@ -244,6 +245,8 @@ void commit_start(BlockDriverState *bs, BlockDriverState *base,
     s->base_flags          = orig_base_flags;
     s->orig_overlay_flags  = orig_overlay_flags;
 
+    s->backing_file_str = g_strdup(backing_file_str);
+
     s->on_error = on_error;
     s->common.co = qemu_coroutine_create(commit_run);
 
diff --git a/block/cow.c b/block/cow.c
index 8f81ee6d56..6ee483327f 100644
--- a/block/cow.c
+++ b/block/cow.c
@@ -332,7 +332,7 @@ static int cow_create(const char *filename, QemuOpts *opts, Error **errp)
     char *image_filename = NULL;
     Error *local_err = NULL;
     int ret;
-    BlockDriverState *cow_bs;
+    BlockDriverState *cow_bs = NULL;
 
     /* Read out options */
     image_sectors = qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0) / 512;
@@ -344,7 +344,6 @@ static int cow_create(const char *filename, QemuOpts *opts, Error **errp)
         goto exit;
     }
 
-    cow_bs = NULL;
     ret = bdrv_open(&cow_bs, filename, NULL, NULL,
                     BDRV_O_RDWR | BDRV_O_PROTOCOL, NULL, &local_err);
     if (ret < 0) {
@@ -383,7 +382,9 @@ static int cow_create(const char *filename, QemuOpts *opts, Error **errp)
 
 exit:
     g_free(image_filename);
-    bdrv_unref(cow_bs);
+    if (cow_bs) {
+        bdrv_unref(cow_bs);
+    }
     return ret;
 }
 
diff --git a/block/qed.c b/block/qed.c
index eddae929eb..b69374b6a2 100644
--- a/block/qed.c
+++ b/block/qed.c
@@ -567,7 +567,7 @@ static void bdrv_qed_close(BlockDriverState *bs)
 static int qed_create(const char *filename, uint32_t cluster_size,
                       uint64_t image_size, uint32_t table_size,
                       const char *backing_file, const char *backing_fmt,
-                      Error **errp)
+                      QemuOpts *opts, Error **errp)
 {
     QEDHeader header = {
         .magic = QED_MAGIC,
@@ -586,7 +586,7 @@ static int qed_create(const char *filename, uint32_t cluster_size,
     int ret = 0;
     BlockDriverState *bs;
 
-    ret = bdrv_create_file(filename, NULL, &local_err);
+    ret = bdrv_create_file(filename, opts, &local_err);
     if (ret < 0) {
         error_propagate(errp, local_err);
         return ret;
@@ -682,7 +682,7 @@ static int bdrv_qed_create(const char *filename, QemuOpts *opts, Error **errp)
     }
 
     ret = qed_create(filename, cluster_size, image_size, table_size,
-                     backing_file, backing_fmt, errp);
+                     backing_file, backing_fmt, opts, errp);
 
 finish:
     g_free(backing_file);
diff --git a/block/raw-posix.c b/block/raw-posix.c
index dacf4fbbc8..825a0c878f 100644
--- a/block/raw-posix.c
+++ b/block/raw-posix.c
@@ -55,6 +55,9 @@
 #include <linux/cdrom.h>
 #include <linux/fd.h>
 #include <linux/fs.h>
+#ifndef FS_NOCOW_FL
+#define FS_NOCOW_FL                     0x00800000 /* Do not cow file */
+#endif
 #endif
 #ifdef CONFIG_FIEMAP
 #include <linux/fiemap.h>
@@ -1278,12 +1281,14 @@ static int raw_create(const char *filename, QemuOpts *opts, Error **errp)
     int fd;
     int result = 0;
     int64_t total_size = 0;
+    bool nocow = false;
 
     strstart(filename, "file:", &filename);
 
     /* Read out options */
     total_size =
         qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0) / BDRV_SECTOR_SIZE;
+    nocow = qemu_opt_get_bool(opts, BLOCK_OPT_NOCOW, false);
 
     fd = qemu_open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,
                    0644);
@@ -1291,6 +1296,21 @@ static int raw_create(const char *filename, QemuOpts *opts, Error **errp)
         result = -errno;
         error_setg_errno(errp, -result, "Could not create file");
     } else {
+        if (nocow) {
+#ifdef __linux__
+            /* Set NOCOW flag to solve performance issue on fs like btrfs.
+             * This is an optimisation. The FS_IOC_SETFLAGS ioctl return value
+             * will be ignored since any failure of this operation should not
+             * block the left work.
+             */
+            int attr;
+            if (ioctl(fd, FS_IOC_GETFLAGS, &attr) == 0) {
+                attr |= FS_NOCOW_FL;
+                ioctl(fd, FS_IOC_SETFLAGS, &attr);
+            }
+#endif
+        }
+
         if (ftruncate(fd, total_size * BDRV_SECTOR_SIZE) != 0) {
             result = -errno;
             error_setg_errno(errp, -result, "Could not resize file");
@@ -1477,6 +1497,11 @@ static QemuOptsList raw_create_opts = {
             .type = QEMU_OPT_SIZE,
             .help = "Virtual disk size"
         },
+        {
+            .name = BLOCK_OPT_NOCOW,
+            .type = QEMU_OPT_BOOL,
+            .help = "Turn off copy-on-write (valid only on btrfs)"
+        },
         { /* end of list */ }
     }
 };
diff --git a/block/stream.c b/block/stream.c
index 043340994d..34de8ba0d9 100644
--- a/block/stream.c
+++ b/block/stream.c
@@ -32,7 +32,7 @@ typedef struct StreamBlockJob {
     RateLimit limit;
     BlockDriverState *base;
     BlockdevOnError on_error;
-    char backing_file_id[1024];
+    char *backing_file_str;
 } StreamBlockJob;
 
 static int coroutine_fn stream_populate(BlockDriverState *bs,
@@ -186,7 +186,7 @@ wait:
     if (!block_job_is_cancelled(&s->common) && sector_num == end && ret == 0) {
         const char *base_id = NULL, *base_fmt = NULL;
         if (base) {
-            base_id = s->backing_file_id;
+            base_id = s->backing_file_str;
             if (base->drv) {
                 base_fmt = base->drv->format_name;
             }
@@ -196,6 +196,7 @@ wait:
     }
 
     qemu_vfree(buf);
+    g_free(s->backing_file_str);
     block_job_completed(&s->common, ret);
 }
 
@@ -217,7 +218,7 @@ static const BlockJobDriver stream_job_driver = {
 };
 
 void stream_start(BlockDriverState *bs, BlockDriverState *base,
-                  const char *base_id, int64_t speed,
+                  const char *backing_file_str, int64_t speed,
                   BlockdevOnError on_error,
                   BlockDriverCompletionFunc *cb,
                   void *opaque, Error **errp)
@@ -237,9 +238,7 @@ void stream_start(BlockDriverState *bs, BlockDriverState *base,
     }
 
     s->base = base;
-    if (base_id) {
-        pstrcpy(s->backing_file_id, sizeof(s->backing_file_id), base_id);
-    }
+    s->backing_file_str = g_strdup(backing_file_str);
 
     s->on_error = on_error;
     s->common.co = qemu_coroutine_create(stream_run);
diff --git a/block/vdi.c b/block/vdi.c
index 01fe22ebe8..197bd77c97 100644
--- a/block/vdi.c
+++ b/block/vdi.c
@@ -53,6 +53,13 @@
 #include "block/block_int.h"
 #include "qemu/module.h"
 #include "migration/migration.h"
+#ifdef __linux__
+#include <linux/fs.h>
+#include <sys/ioctl.h>
+#ifndef FS_NOCOW_FL
+#define FS_NOCOW_FL                     0x00800000 /* Do not cow file */
+#endif
+#endif
 
 #if defined(CONFIG_UUID)
 #include <uuid/uuid.h>
@@ -683,6 +690,7 @@ static int vdi_create(const char *filename, QemuOpts *opts, Error **errp)
     VdiHeader header;
     size_t i;
     size_t bmap_size;
+    bool nocow = false;
 
     logout("\n");
 
@@ -699,6 +707,7 @@ static int vdi_create(const char *filename, QemuOpts *opts, Error **errp)
         image_type = VDI_TYPE_STATIC;
     }
 #endif
+    nocow = qemu_opt_get_bool_del(opts, BLOCK_OPT_NOCOW, false);
 
     if (bytes > VDI_DISK_SIZE_MAX) {
         result = -ENOTSUP;
@@ -716,6 +725,21 @@ static int vdi_create(const char *filename, QemuOpts *opts, Error **errp)
         goto exit;
     }
 
+    if (nocow) {
+#ifdef __linux__
+        /* Set NOCOW flag to solve performance issue on fs like btrfs.
+         * This is an optimisation. The FS_IOC_SETFLAGS ioctl return value will
+         * be ignored since any failure of this operation should not block the
+         * left work.
+         */
+        int attr;
+        if (ioctl(fd, FS_IOC_GETFLAGS, &attr) == 0) {
+            attr |= FS_NOCOW_FL;
+            ioctl(fd, FS_IOC_SETFLAGS, &attr);
+        }
+#endif
+    }
+
     /* We need enough blocks to store the given disk size,
        so always round up. */
     blocks = (bytes + block_size - 1) / block_size;
@@ -818,6 +842,11 @@ static QemuOptsList vdi_create_opts = {
             .def_value_str = "off"
         },
 #endif
+        {
+            .name = BLOCK_OPT_NOCOW,
+            .type = QEMU_OPT_BOOL,
+            .help = "Turn off copy-on-write (valid only on btrfs)"
+        },
         /* TODO: An additional option to set UUID values might be useful. */
         { /* end of list */ }
     }
diff --git a/block/vmdk.c b/block/vmdk.c
index d0de0193fc..27a78daa02 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -1529,7 +1529,7 @@ static int coroutine_fn vmdk_co_write_zeroes(BlockDriverState *bs,
 
 static int vmdk_create_extent(const char *filename, int64_t filesize,
                               bool flat, bool compress, bool zeroed_grain,
-                              Error **errp)
+                              QemuOpts *opts, Error **errp)
 {
     int ret, i;
     BlockDriverState *bs = NULL;
@@ -1539,7 +1539,7 @@ static int vmdk_create_extent(const char *filename, int64_t filesize,
     uint32_t *gd_buf = NULL;
     int gd_buf_size;
 
-    ret = bdrv_create_file(filename, NULL, &local_err);
+    ret = bdrv_create_file(filename, opts, &local_err);
     if (ret < 0) {
         error_propagate(errp, local_err);
         goto exit;
@@ -1845,7 +1845,7 @@ static int vmdk_create(const char *filename, QemuOpts *opts, Error **errp)
                 path, desc_filename);
 
         if (vmdk_create_extent(ext_filename, size,
-                               flat, compress, zeroed_grain, errp)) {
+                               flat, compress, zeroed_grain, opts, errp)) {
             ret = -EINVAL;
             goto exit;
         }
diff --git a/block/vpc.c b/block/vpc.c
index 798d8540db..8b376a40be 100644
--- a/block/vpc.c
+++ b/block/vpc.c
@@ -29,6 +29,13 @@
 #if defined(CONFIG_UUID)
 #include <uuid/uuid.h>
 #endif
+#ifdef __linux__
+#include <linux/fs.h>
+#include <sys/ioctl.h>
+#ifndef FS_NOCOW_FL
+#define FS_NOCOW_FL                     0x00800000 /* Do not cow file */
+#endif
+#endif
 
 /**************************************************************/
 
@@ -751,6 +758,7 @@ static int vpc_create(const char *filename, QemuOpts *opts, Error **errp)
     int64_t total_size;
     int disk_type;
     int ret = -EIO;
+    bool nocow = false;
 
     /* Read out options */
     total_size = qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0);
@@ -767,6 +775,7 @@ static int vpc_create(const char *filename, QemuOpts *opts, Error **errp)
     } else {
         disk_type = VHD_DYNAMIC;
     }
+    nocow = qemu_opt_get_bool_del(opts, BLOCK_OPT_NOCOW, false);
 
     /* Create the file */
     fd = qemu_open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, 0644);
@@ -775,6 +784,21 @@ static int vpc_create(const char *filename, QemuOpts *opts, Error **errp)
         goto out;
     }
 
+    if (nocow) {
+#ifdef __linux__
+        /* Set NOCOW flag to solve performance issue on fs like btrfs.
+         * This is an optimisation. The FS_IOC_SETFLAGS ioctl return value will
+         * be ignored since any failure of this operation should not block the
+         * left work.
+         */
+        int attr;
+        if (ioctl(fd, FS_IOC_GETFLAGS, &attr) == 0) {
+            attr |= FS_NOCOW_FL;
+            ioctl(fd, FS_IOC_SETFLAGS, &attr);
+        }
+#endif
+    }
+
     /*
      * Calculate matching total_size and geometry. Increase the number of
      * sectors requested until we get enough (or fail). This ensures that
@@ -884,6 +908,11 @@ static QemuOptsList vpc_create_opts = {
                 "Type of virtual hard disk format. Supported formats are "
                 "{dynamic (default) | fixed} "
         },
+        {
+            .name = BLOCK_OPT_NOCOW,
+            .type = QEMU_OPT_BOOL,
+            .help = "Turn off copy-on-write (valid only on btrfs)"
+        },
         { /* end of list */ }
     }
 };
diff --git a/blockdev.c b/blockdev.c
index 69b7c2a8c5..48bd9a37bc 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1871,14 +1871,17 @@ static void block_job_cb(void *opaque, int ret)
     bdrv_put_ref_bh_schedule(bs);
 }
 
-void qmp_block_stream(const char *device, bool has_base,
-                      const char *base, bool has_speed, int64_t speed,
+void qmp_block_stream(const char *device,
+                      bool has_base, const char *base,
+                      bool has_backing_file, const char *backing_file,
+                      bool has_speed, int64_t speed,
                       bool has_on_error, BlockdevOnError on_error,
                       Error **errp)
 {
     BlockDriverState *bs;
     BlockDriverState *base_bs = NULL;
     Error *local_err = NULL;
+    const char *base_name = NULL;
 
     if (!has_on_error) {
         on_error = BLOCKDEV_ON_ERROR_REPORT;
@@ -1894,15 +1897,27 @@ void qmp_block_stream(const char *device, bool has_base,
         return;
     }
 
-    if (base) {
+    if (has_base) {
         base_bs = bdrv_find_backing_image(bs, base);
         if (base_bs == NULL) {
             error_set(errp, QERR_BASE_NOT_FOUND, base);
             return;
         }
+        base_name = base;
+    }
+
+    /* if we are streaming the entire chain, the result will have no backing
+     * file, and specifying one is therefore an error */
+    if (base_bs == NULL && has_backing_file) {
+        error_setg(errp, "backing file specified, but streaming the "
+                         "entire chain");
+        return;
     }
 
-    stream_start(bs, base_bs, base, has_speed ? speed : 0,
+    /* backing_file string overrides base bs filename */
+    base_name = has_backing_file ? backing_file : base_name;
+
+    stream_start(bs, base_bs, base_name, has_speed ? speed : 0,
                  on_error, block_job_cb, bs, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
@@ -1913,7 +1928,9 @@ void qmp_block_stream(const char *device, bool has_base,
 }
 
 void qmp_block_commit(const char *device,
-                      bool has_base, const char *base, const char *top,
+                      bool has_base, const char *base,
+                      bool has_top, const char *top,
+                      bool has_backing_file, const char *backing_file,
                       bool has_speed, int64_t speed,
                       Error **errp)
 {
@@ -1932,6 +1949,11 @@ void qmp_block_commit(const char *device,
     /* drain all i/o before commits */
     bdrv_drain_all();
 
+    /* Important Note:
+     *  libvirt relies on the DeviceNotFound error class in order to probe for
+     *  live commit feature versions; for this to work, we must make sure to
+     *  perform the device lookup before any generic errors that may occur in a
+     *  scenario in which all optional arguments are omitted. */
     bs = bdrv_find(device);
     if (!bs) {
         error_set(errp, QERR_DEVICE_NOT_FOUND, device);
@@ -1945,7 +1967,7 @@ void qmp_block_commit(const char *device,
     /* default top_bs is the active layer */
     top_bs = bs;
 
-    if (top) {
+    if (has_top && top) {
         if (strcmp(bs->filename, top) != 0) {
             top_bs = bdrv_find_backing_image(bs, top);
         }
@@ -1967,12 +1989,23 @@ void qmp_block_commit(const char *device,
         return;
     }
 
+    /* Do not allow attempts to commit an image into itself */
+    if (top_bs == base_bs) {
+        error_setg(errp, "cannot commit an image into itself");
+        return;
+    }
+
     if (top_bs == bs) {
+        if (has_backing_file) {
+            error_setg(errp, "'backing-file' specified,"
+                             " but 'top' is the active layer");
+            return;
+        }
         commit_active_start(bs, base_bs, speed, on_error, block_job_cb,
                             bs, &local_err);
     } else {
         commit_start(bs, base_bs, top_bs, speed, on_error, block_job_cb, bs,
-                    &local_err);
+                     has_backing_file ? backing_file : NULL, &local_err);
     }
     if (local_err != NULL) {
         error_propagate(errp, local_err);
@@ -2355,6 +2388,85 @@ void qmp_block_job_complete(const char *device, Error **errp)
     block_job_complete(job, errp);
 }
 
+void qmp_change_backing_file(const char *device,
+                             const char *image_node_name,
+                             const char *backing_file,
+                             Error **errp)
+{
+    BlockDriverState *bs = NULL;
+    BlockDriverState *image_bs = NULL;
+    Error *local_err = NULL;
+    bool ro;
+    int open_flags;
+    int ret;
+
+    /* find the top layer BDS of the chain */
+    bs = bdrv_find(device);
+    if (!bs) {
+        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
+        return;
+    }
+
+    image_bs = bdrv_lookup_bs(NULL, image_node_name, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return;
+    }
+
+    if (!image_bs) {
+        error_setg(errp, "image file not found");
+        return;
+    }
+
+    if (bdrv_find_base(image_bs) == image_bs) {
+        error_setg(errp, "not allowing backing file change on an image "
+                         "without a backing file");
+        return;
+    }
+
+    /* even though we are not necessarily operating on bs, we need it to
+     * determine if block ops are currently prohibited on the chain */
+    if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_CHANGE, errp)) {
+        return;
+    }
+
+    /* final sanity check */
+    if (!bdrv_chain_contains(bs, image_bs)) {
+        error_setg(errp, "'%s' and image file are not in the same chain",
+                   device);
+        return;
+    }
+
+    /* if not r/w, reopen to make r/w */
+    open_flags = image_bs->open_flags;
+    ro = bdrv_is_read_only(image_bs);
+
+    if (ro) {
+        bdrv_reopen(image_bs, open_flags | BDRV_O_RDWR, &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
+            return;
+        }
+    }
+
+    ret = bdrv_change_backing_file(image_bs, backing_file,
+                               image_bs->drv ? image_bs->drv->format_name : "");
+
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "Could not change backing file to '%s'",
+                         backing_file);
+        /* don't exit here, so we can try to restore open flags if
+         * appropriate */
+    }
+
+    if (ro) {
+        bdrv_reopen(image_bs, open_flags, &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err); /* will preserve prior errp */
+        }
+    }
+}
+
 void qmp_blockdev_add(BlockdevOptions *options, Error **errp)
 {
     QmpOutputVisitor *ov = qmp_output_visitor_new();
diff --git a/docs/qmp/qmp-events.txt b/docs/qmp/qmp-events.txt
index 44be891261..4a6c2a2c45 100644
--- a/docs/qmp/qmp-events.txt
+++ b/docs/qmp/qmp-events.txt
@@ -250,14 +250,14 @@ Emitted by the Quorum block driver if it fails to establish a quorum.
 
 Data:
 
-- "reference":    device name if defined else node name.
-- "sector-num":   Number of the first sector of the failed read operation.
-- "sector-count": Failed read operation sector count.
+- "reference":     device name if defined else node name.
+- "sector-num":    Number of the first sector of the failed read operation.
+- "sectors-count": Failed read operation sector count.
 
 Example:
 
 { "event": "QUORUM_FAILURE",
-     "data": { "reference": "usr1", "sector-num": 345435, "sector-count": 5 },
+     "data": { "reference": "usr1", "sector-num": 345435, "sectors-count": 5 },
      "timestamp": { "seconds": 1344522075, "microseconds": 745528 } }
 
 QUORUM_REPORT_BAD
@@ -267,19 +267,19 @@ Emitted to report a corruption of a Quorum file.
 
 Data:
 
-- "error":        Error message (json-string, optional)
-                  Only present on failure.  This field contains a human-readable
-                  error message.  There are no semantics other than that the
-                  block layer reported an error and clients should not try to
-                  interpret the error string.
-- "node-name":    The graph node name of the block driver state.
-- "sector-num":   Number of the first sector of the failed read operation.
-- "sector-count": Failed read operation sector count.
+- "error":         Error message (json-string, optional)
+                   Only present on failure.  This field contains a human-readable
+                   error message.  There are no semantics other than that the
+                   block layer reported an error and clients should not try to
+                   interpret the error string.
+- "node-name":     The graph node name of the block driver state.
+- "sector-num":    Number of the first sector of the failed read operation.
+- "sectors-count": Failed read operation sector count.
 
 Example:
 
 { "event": "QUORUM_REPORT_BAD",
-     "data": { "node-name": "1.raw", "sector-num": 345435, "sector-count": 5 },
+     "data": { "node-name": "1.raw", "sector-num": 345435, "sectors-count": 5 },
      "timestamp": { "seconds": 1344522075, "microseconds": 745528 } }
 
 RESET
diff --git a/hmp.c b/hmp.c
index 6429e6b447..4d1838e9ea 100644
--- a/hmp.c
+++ b/hmp.c
@@ -1176,7 +1176,7 @@ void hmp_block_stream(Monitor *mon, const QDict *qdict)
     const char *base = qdict_get_try_str(qdict, "base");
     int64_t speed = qdict_get_try_int(qdict, "speed", 0);
 
-    qmp_block_stream(device, base != NULL, base,
+    qmp_block_stream(device, base != NULL, base, false, NULL,
                      qdict_haskey(qdict, "speed"), speed,
                      true, BLOCKDEV_ON_ERROR_REPORT, &error);
 
diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index 09bd2c70ab..4c5ba18122 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -127,10 +127,20 @@ void virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *blk,
     VirtIOBlockDataPlane *s;
     VirtIOBlock *vblk = VIRTIO_BLK(vdev);
     Error *local_err = NULL;
+    BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(vdev)));
+    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
 
     *dataplane = NULL;
 
-    if (!blk->data_plane) {
+    if (!blk->data_plane && !blk->iothread) {
+        return;
+    }
+
+    /* Don't try if transport does not support notifiers. */
+    if (!k->set_guest_notifiers || !k->set_host_notifier) {
+        error_setg(errp,
+                   "device is incompatible with x-data-plane "
+                   "(transport does not support notifiers)");
         return;
     }
 
diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
index e59ebc962d..aec3146755 100644
--- a/hw/block/virtio-blk.c
+++ b/hw/block/virtio-blk.c
@@ -677,12 +677,6 @@ static const BlockDevOps virtio_block_ops = {
     .resize_cb = virtio_blk_resize,
 };
 
-void virtio_blk_set_conf(DeviceState *dev, VirtIOBlkConf *blk)
-{
-    VirtIOBlock *s = VIRTIO_BLK(dev);
-    memcpy(&(s->blk), blk, sizeof(struct VirtIOBlkConf));
-}
-
 #ifdef CONFIG_VIRTIO_BLK_DATA_PLANE
 /* Disable dataplane thread during live migration since it does not
  * update the dirty memory bitmap yet.
@@ -790,8 +784,27 @@ static void virtio_blk_device_unrealize(DeviceState *dev, Error **errp)
     virtio_cleanup(vdev);
 }
 
+static void virtio_blk_instance_init(Object *obj)
+{
+    VirtIOBlock *s = VIRTIO_BLK(obj);
+
+    object_property_add_link(obj, "iothread", TYPE_IOTHREAD,
+                             (Object **)&s->blk.iothread,
+                             qdev_prop_allow_set_link_before_realize,
+                             OBJ_PROP_LINK_UNREF_ON_RELEASE, NULL);
+}
+
 static Property virtio_blk_properties[] = {
-    DEFINE_VIRTIO_BLK_PROPERTIES(VirtIOBlock, blk),
+    DEFINE_BLOCK_PROPERTIES(VirtIOBlock, blk.conf),
+    DEFINE_BLOCK_CHS_PROPERTIES(VirtIOBlock, blk.conf),
+    DEFINE_PROP_STRING("serial", VirtIOBlock, blk.serial),
+    DEFINE_PROP_BIT("config-wce", VirtIOBlock, blk.config_wce, 0, true),
+#ifdef __linux__
+    DEFINE_PROP_BIT("scsi", VirtIOBlock, blk.scsi, 0, true),
+#endif
+#ifdef CONFIG_VIRTIO_BLK_DATA_PLANE
+    DEFINE_PROP_BIT("x-data-plane", VirtIOBlock, blk.data_plane, 0, false),
+#endif
     DEFINE_PROP_END_OF_LIST(),
 };
 
@@ -817,6 +830,7 @@ static const TypeInfo virtio_device_info = {
     .name = TYPE_VIRTIO_BLK,
     .parent = TYPE_VIRTIO_DEVICE,
     .instance_size = sizeof(VirtIOBlock),
+    .instance_init = virtio_blk_instance_init,
     .class_init = virtio_blk_class_init,
 };
 
diff --git a/hw/core/qdev-properties-system.c b/hw/core/qdev-properties-system.c
index 52c2f8afa5..8e140af46f 100644
--- a/hw/core/qdev-properties-system.c
+++ b/hw/core/qdev-properties-system.c
@@ -385,56 +385,6 @@ void qdev_set_nic_properties(DeviceState *dev, NICInfo *nd)
     nd->instantiated = 1;
 }
 
-/* --- iothread --- */
-
-static char *print_iothread(void *ptr)
-{
-    return iothread_get_id(ptr);
-}
-
-static int parse_iothread(DeviceState *dev, const char *str, void **ptr)
-{
-    IOThread *iothread;
-
-    iothread = iothread_find(str);
-    if (!iothread) {
-        return -ENOENT;
-    }
-    object_ref(OBJECT(iothread));
-    *ptr = iothread;
-    return 0;
-}
-
-static void get_iothread(Object *obj, struct Visitor *v, void *opaque,
-                         const char *name, Error **errp)
-{
-    get_pointer(obj, v, opaque, print_iothread, name, errp);
-}
-
-static void set_iothread(Object *obj, struct Visitor *v, void *opaque,
-                         const char *name, Error **errp)
-{
-    set_pointer(obj, v, opaque, parse_iothread, name, errp);
-}
-
-static void release_iothread(Object *obj, const char *name, void *opaque)
-{
-    DeviceState *dev = DEVICE(obj);
-    Property *prop = opaque;
-    IOThread **ptr = qdev_get_prop_ptr(dev, prop);
-
-    if (*ptr) {
-        object_unref(OBJECT(*ptr));
-    }
-}
-
-PropertyInfo qdev_prop_iothread = {
-    .name = "iothread",
-    .get = get_iothread,
-    .set = set_iothread,
-    .release = release_iothread,
-};
-
 static int qdev_add_one_global(QemuOpts *opts, void *opaque)
 {
     GlobalProperty *g;
diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index a2feb5abfe..3bdda8ef66 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -780,6 +780,27 @@ void qdev_property_add_static(DeviceState *dev, Property *prop,
     }
 }
 
+/* @qdev_alias_all_properties - Add alias properties to the source object for
+ * all qdev properties on the target DeviceState.
+ */
+void qdev_alias_all_properties(DeviceState *target, Object *source)
+{
+    ObjectClass *class;
+    Property *prop;
+
+    class = object_get_class(OBJECT(target));
+    do {
+        DeviceClass *dc = DEVICE_CLASS(class);
+
+        for (prop = dc->props; prop && prop->name; prop++) {
+            object_property_add_alias(source, prop->name,
+                                      OBJECT(target), prop->name,
+                                      &error_abort);
+        }
+        class = object_class_get_parent(class);
+    } while (class != object_class_by_name(TYPE_DEVICE));
+}
+
 static bool device_get_realized(Object *obj, Error **errp)
 {
     DeviceState *dev = DEVICE(obj);
diff --git a/hw/s390x/s390-virtio-bus.c b/hw/s390x/s390-virtio-bus.c
index 7c8c81b0cc..c0dc3658c7 100644
--- a/hw/s390x/s390-virtio-bus.c
+++ b/hw/s390x/s390-virtio-bus.c
@@ -167,7 +167,6 @@ static int s390_virtio_blk_init(VirtIOS390Device *s390_dev)
 {
     VirtIOBlkS390 *dev = VIRTIO_BLK_S390(s390_dev);
     DeviceState *vdev = DEVICE(&dev->vdev);
-    virtio_blk_set_conf(vdev, &(dev->blk));
     qdev_set_parent_bus(vdev, BUS(&s390_dev->bus));
     if (qdev_init(vdev) < 0) {
         return -1;
@@ -180,6 +179,10 @@ static void s390_virtio_blk_instance_init(Object *obj)
     VirtIOBlkS390 *dev = VIRTIO_BLK_S390(obj);
     object_initialize(&dev->vdev, sizeof(dev->vdev), TYPE_VIRTIO_BLK);
     object_property_add_child(obj, "virtio-backend", OBJECT(&dev->vdev), NULL);
+    object_unref(OBJECT(&dev->vdev));
+    qdev_alias_all_properties(DEVICE(&dev->vdev), obj);
+    object_property_add_alias(obj, "iothread", OBJECT(&dev->vdev),"iothread",
+                              &error_abort);
 }
 
 static int s390_virtio_serial_init(VirtIOS390Device *s390_dev)
@@ -513,18 +516,11 @@ static const TypeInfo s390_virtio_net = {
     .class_init    = s390_virtio_net_class_init,
 };
 
-static Property s390_virtio_blk_properties[] = {
-    DEFINE_VIRTIO_BLK_PROPERTIES(VirtIOBlkS390, blk),
-    DEFINE_PROP_END_OF_LIST(),
-};
-
 static void s390_virtio_blk_class_init(ObjectClass *klass, void *data)
 {
-    DeviceClass *dc = DEVICE_CLASS(klass);
     VirtIOS390DeviceClass *k = VIRTIO_S390_DEVICE_CLASS(klass);
 
     k->init = s390_virtio_blk_init;
-    dc->props = s390_virtio_blk_properties;
 }
 
 static const TypeInfo s390_virtio_blk = {
diff --git a/hw/s390x/s390-virtio-bus.h b/hw/s390x/s390-virtio-bus.h
index ac81bd89ee..ffd0df708b 100644
--- a/hw/s390x/s390-virtio-bus.h
+++ b/hw/s390x/s390-virtio-bus.h
@@ -124,7 +124,6 @@ void s390_virtio_reset_idx(VirtIOS390Device *dev);
 typedef struct VirtIOBlkS390 {
     VirtIOS390Device parent_obj;
     VirtIOBlock vdev;
-    VirtIOBlkConf blk;
 } VirtIOBlkS390;
 
 /* virtio-scsi-s390 */
diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
index 05656a2887..c2799685f2 100644
--- a/hw/s390x/virtio-ccw.c
+++ b/hw/s390x/virtio-ccw.c
@@ -800,7 +800,6 @@ static int virtio_ccw_blk_init(VirtioCcwDevice *ccw_dev)
 {
     VirtIOBlkCcw *dev = VIRTIO_BLK_CCW(ccw_dev);
     DeviceState *vdev = DEVICE(&dev->vdev);
-    virtio_blk_set_conf(vdev, &(dev->blk));
     qdev_set_parent_bus(vdev, BUS(&ccw_dev->bus));
     if (qdev_init(vdev) < 0) {
         return -1;
@@ -814,6 +813,10 @@ static void virtio_ccw_blk_instance_init(Object *obj)
     VirtIOBlkCcw *dev = VIRTIO_BLK_CCW(obj);
     object_initialize(&dev->vdev, sizeof(dev->vdev), TYPE_VIRTIO_BLK);
     object_property_add_child(obj, "virtio-backend", OBJECT(&dev->vdev), NULL);
+    object_unref(OBJECT(&dev->vdev));
+    qdev_alias_all_properties(DEVICE(&dev->vdev), obj);
+    object_property_add_alias(obj, "iothread", OBJECT(&dev->vdev),"iothread",
+                              &error_abort);
 }
 
 static int virtio_ccw_serial_init(VirtioCcwDevice *ccw_dev)
@@ -1400,12 +1403,8 @@ static const TypeInfo virtio_ccw_net = {
 static Property virtio_ccw_blk_properties[] = {
     DEFINE_PROP_STRING("devno", VirtioCcwDevice, bus_id),
     DEFINE_VIRTIO_BLK_FEATURES(VirtioCcwDevice, host_features[0]),
-    DEFINE_VIRTIO_BLK_PROPERTIES(VirtIOBlkCcw, blk),
     DEFINE_PROP_BIT("ioeventfd", VirtioCcwDevice, flags,
                     VIRTIO_CCW_FLAG_USE_IOEVENTFD_BIT, true),
-#ifdef CONFIG_VIRTIO_BLK_DATA_PLANE
-    DEFINE_PROP_BIT("x-data-plane", VirtIOBlkCcw, blk.data_plane, 0, false),
-#endif
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/hw/s390x/virtio-ccw.h b/hw/s390x/virtio-ccw.h
index b8b8a8abaa..5a1f16ee5d 100644
--- a/hw/s390x/virtio-ccw.h
+++ b/hw/s390x/virtio-ccw.h
@@ -144,7 +144,6 @@ typedef struct VHostSCSICcw {
 typedef struct VirtIOBlkCcw {
     VirtioCcwDevice parent_obj;
     VirtIOBlock vdev;
-    VirtIOBlkConf blk;
 } VirtIOBlkCcw;
 
 /* virtio-balloon-ccw */
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 317324f23d..3c42cda82b 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -1066,11 +1066,7 @@ static Property virtio_blk_pci_properties[] = {
     DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
                     VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
     DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 2),
-#ifdef CONFIG_VIRTIO_BLK_DATA_PLANE
-    DEFINE_PROP_BIT("x-data-plane", VirtIOBlkPCI, blk.data_plane, 0, false),
-#endif
     DEFINE_VIRTIO_BLK_FEATURES(VirtIOPCIProxy, host_features),
-    DEFINE_VIRTIO_BLK_PROPERTIES(VirtIOBlkPCI, blk),
     DEFINE_PROP_END_OF_LIST(),
 };
 
@@ -1078,7 +1074,6 @@ static int virtio_blk_pci_init(VirtIOPCIProxy *vpci_dev)
 {
     VirtIOBlkPCI *dev = VIRTIO_BLK_PCI(vpci_dev);
     DeviceState *vdev = DEVICE(&dev->vdev);
-    virtio_blk_set_conf(vdev, &(dev->blk));
     qdev_set_parent_bus(vdev, BUS(&vpci_dev->bus));
     if (qdev_init(vdev) < 0) {
         return -1;
@@ -1106,6 +1101,10 @@ static void virtio_blk_pci_instance_init(Object *obj)
     VirtIOBlkPCI *dev = VIRTIO_BLK_PCI(obj);
     object_initialize(&dev->vdev, sizeof(dev->vdev), TYPE_VIRTIO_BLK);
     object_property_add_child(obj, "virtio-backend", OBJECT(&dev->vdev), NULL);
+    object_unref(OBJECT(&dev->vdev));
+    qdev_alias_all_properties(DEVICE(&dev->vdev), obj);
+    object_property_add_alias(obj, "iothread", OBJECT(&dev->vdev),"iothread",
+                              &error_abort);
 }
 
 static const TypeInfo virtio_blk_pci_info = {
diff --git a/hw/virtio/virtio-pci.h b/hw/virtio/virtio-pci.h
index dc332ae774..1cea157a47 100644
--- a/hw/virtio/virtio-pci.h
+++ b/hw/virtio/virtio-pci.h
@@ -131,7 +131,6 @@ struct VHostSCSIPCI {
 struct VirtIOBlkPCI {
     VirtIOPCIProxy parent_obj;
     VirtIOBlock vdev;
-    VirtIOBlkConf blk;
 };
 
 /*
diff --git a/include/block/block.h b/include/block/block.h
index 7e92f549fb..baecc26dfc 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -285,7 +285,8 @@ int bdrv_change_backing_file(BlockDriverState *bs,
     const char *backing_file, const char *backing_fmt);
 void bdrv_register(BlockDriver *bdrv);
 int bdrv_drop_intermediate(BlockDriverState *active, BlockDriverState *top,
-                           BlockDriverState *base);
+                           BlockDriverState *base,
+                           const char *backing_file_str);
 BlockDriverState *bdrv_find_overlay(BlockDriverState *active,
                                     BlockDriverState *bs);
 BlockDriverState *bdrv_find_base(BlockDriverState *bs);
@@ -403,6 +404,7 @@ BlockDeviceInfoList *bdrv_named_nodes_list(void);
 BlockDriverState *bdrv_lookup_bs(const char *device,
                                  const char *node_name,
                                  Error **errp);
+bool bdrv_chain_contains(BlockDriverState *top, BlockDriverState *base);
 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 53e77cf11e..8f8e65e763 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -54,6 +54,7 @@
 #define BLOCK_OPT_LAZY_REFCOUNTS    "lazy_refcounts"
 #define BLOCK_OPT_ADAPTER_TYPE      "adapter_type"
 #define BLOCK_OPT_REDUNDANCY        "redundancy"
+#define BLOCK_OPT_NOCOW             "nocow"
 
 typedef struct BdrvTrackedRequest {
     BlockDriverState *bs;
@@ -462,13 +463,14 @@ void stream_start(BlockDriverState *bs, BlockDriverState *base,
  * @on_error: The action to take upon error.
  * @cb: Completion function for the job.
  * @opaque: Opaque pointer value passed to @cb.
+ * @backing_file_str: String to use as the backing file in @top's overlay
  * @errp: Error object.
  *
  */
 void commit_start(BlockDriverState *bs, BlockDriverState *base,
                  BlockDriverState *top, int64_t speed,
                  BlockdevOnError on_error, BlockDriverCompletionFunc *cb,
-                 void *opaque, Error **errp);
+                 void *opaque, const char *backing_file_str, Error **errp);
 /**
  * commit_active_start:
  * @bs: Active block device to be committed.
diff --git a/include/hw/qdev-properties.h b/include/hw/qdev-properties.h
index c962b6bbaa..77fe3a12b7 100644
--- a/include/hw/qdev-properties.h
+++ b/include/hw/qdev-properties.h
@@ -22,7 +22,6 @@ extern PropertyInfo qdev_prop_bios_chs_trans;
 extern PropertyInfo qdev_prop_drive;
 extern PropertyInfo qdev_prop_netdev;
 extern PropertyInfo qdev_prop_vlan;
-extern PropertyInfo qdev_prop_iothread;
 extern PropertyInfo qdev_prop_pci_devfn;
 extern PropertyInfo qdev_prop_blocksize;
 extern PropertyInfo qdev_prop_pci_host_devaddr;
@@ -143,8 +142,6 @@ extern PropertyInfo qdev_prop_arraylen;
     DEFINE_PROP(_n, _s, _f, qdev_prop_vlan, NICPeers)
 #define DEFINE_PROP_DRIVE(_n, _s, _f) \
     DEFINE_PROP(_n, _s, _f, qdev_prop_drive, BlockDriverState *)
-#define DEFINE_PROP_IOTHREAD(_n, _s, _f)             \
-    DEFINE_PROP(_n, _s, _f, qdev_prop_iothread, IOThread *)
 #define DEFINE_PROP_MACADDR(_n, _s, _f)         \
     DEFINE_PROP(_n, _s, _f, qdev_prop_macaddr, MACAddr)
 #define DEFINE_PROP_LOSTTICKPOLICY(_n, _s, _f, _d) \
@@ -193,6 +190,8 @@ void error_set_from_qdev_prop_error(Error **errp, int ret, DeviceState *dev,
  */
 void qdev_property_add_static(DeviceState *dev, Property *prop, Error **errp);
 
+void qdev_alias_all_properties(DeviceState *target, Object *source);
+
 /**
  * @qdev_prop_set_after_realize:
  * @dev: device
diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index d0fb26f963..223530e18a 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -155,25 +155,6 @@ typedef struct VirtIOBlockReq {
 #define DEFINE_VIRTIO_BLK_FEATURES(_state, _field) \
         DEFINE_VIRTIO_COMMON_FEATURES(_state, _field)
 
-#ifdef __linux__
-#define DEFINE_VIRTIO_BLK_PROPERTIES(_state, _field)                          \
-        DEFINE_BLOCK_PROPERTIES(_state, _field.conf),                         \
-        DEFINE_BLOCK_CHS_PROPERTIES(_state, _field.conf),                     \
-        DEFINE_PROP_STRING("serial", _state, _field.serial),                  \
-        DEFINE_PROP_BIT("config-wce", _state, _field.config_wce, 0, true),    \
-        DEFINE_PROP_BIT("scsi", _state, _field.scsi, 0, true),                \
-        DEFINE_PROP_IOTHREAD("x-iothread", _state, _field.iothread)
-#else
-#define DEFINE_VIRTIO_BLK_PROPERTIES(_state, _field)                          \
-        DEFINE_BLOCK_PROPERTIES(_state, _field.conf),                         \
-        DEFINE_BLOCK_CHS_PROPERTIES(_state, _field.conf),                     \
-        DEFINE_PROP_STRING("serial", _state, _field.serial),                  \
-        DEFINE_PROP_BIT("config-wce", _state, _field.config_wce, 0, true),    \
-        DEFINE_PROP_IOTHREAD("x-iothread", _state, _field.iothread)
-#endif /* __linux__ */
-
-void virtio_blk_set_conf(DeviceState *dev, VirtIOBlkConf *blk);
-
 int virtio_blk_handle_scsi_req(VirtIOBlock *blk,
                                VirtQueueElement *elem);
 
diff --git a/qapi/block-core.json b/qapi/block-core.json
index faf394cc76..e378653a77 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -680,6 +680,32 @@
   'data': 'BlockdevSnapshot' }
 
 ##
+# @change-backing-file
+#
+# Change the backing file in the image file metadata.  This does not
+# cause QEMU to reopen the image file to reparse the backing filename
+# (it may, however, perform a reopen to change permissions from
+# r/o -> r/w -> r/o, if needed). The new backing file string is written
+# into the image file metadata, and the QEMU internal strings are
+# updated.
+#
+# @image-node-name: The name of the block driver state node of the
+#                   image to modify.
+#
+# @device:          The name of the device that owns image-node-name.
+#
+# @backing-file:    The string to write as the backing file.  This
+#                   string is not validated, so care should be taken
+#                   when specifying the string or the image chain may
+#                   not be able to be reopened again.
+#
+# Since: 2.1
+##
+{ 'command': 'change-backing-file',
+  'data': { 'device': 'str', 'image-node-name': 'str',
+            'backing-file': 'str' } }
+
+##
 # @block-commit
 #
 # Live commit of data from overlay image nodes into backing nodes - i.e.,
@@ -690,8 +716,26 @@
 # @base:   #optional The file name of the backing image to write data into.
 #                    If not specified, this is the deepest backing image
 #
-# @top:              The file name of the backing image within the image chain,
-#                    which contains the topmost data to be committed down.
+# @top:    #optional The file name of the backing image within the image chain,
+#                    which contains the topmost data to be committed down. If
+#                    not specified, this is the active layer.
+#
+# @backing-file:  #optional The backing file string to write into the overlay
+#                           image of 'top'.  If 'top' is the active layer,
+#                           specifying a backing file string is an error. This
+#                           filename is not validated.
+#
+#                           If a pathname string is such that it cannot be
+#                           resolved by QEMU, that means that subsequent QMP or
+#                           HMP commands must use node-names for the image in
+#                           question, as filename lookup methods will fail.
+#
+#                           If not specified, QEMU will automatically determine
+#                           the backing file string to use, or error out if
+#                           there is no obvious choice. Care should be taken
+#                           when specifying the string, to specify a valid
+#                           filename or protocol.
+#                           (Since 2.1)
 #
 #                    If top == base, that is an error.
 #                    If top == active, the job will not be completed by itself,
@@ -705,7 +749,6 @@
 #                    size of the smaller top, you can safely truncate it
 #                    yourself once the commit operation successfully completes.
 #
-#
 # @speed:  #optional the maximum speed, in bytes per second
 #
 # Returns: Nothing on success
@@ -719,8 +762,8 @@
 #
 ##
 { 'command': 'block-commit',
-  'data': { 'device': 'str', '*base': 'str', 'top': 'str',
-            '*speed': 'int' } }
+  'data': { 'device': 'str', '*base': 'str', '*top': 'str',
+            '*backing-file': 'str', '*speed': 'int' } }
 
 ##
 # @drive-backup
@@ -879,6 +922,21 @@
 #
 # @base:   #optional the common backing file name
 #
+# @backing-file: #optional The backing file string to write into the active
+#                          layer. This filename is not validated.
+#
+#                          If a pathname string is such that it cannot be
+#                          resolved by QEMU, that means that subsequent QMP or
+#                          HMP commands must use node-names for the image in
+#                          question, as filename lookup methods will fail.
+#
+#                          If not specified, QEMU will automatically determine
+#                          the backing file string to use, or error out if there
+#                          is no obvious choice.  Care should be taken when
+#                          specifying the string, to specify a valid filename or
+#                          protocol.
+#                          (Since 2.1)
+#
 # @speed:  #optional the maximum speed, in bytes per second
 #
 # @on-error: #optional the action to take on an error (default report).
@@ -891,8 +949,8 @@
 # Since: 1.1
 ##
 { 'command': 'block-stream',
-  'data': { 'device': 'str', '*base': 'str', '*speed': 'int',
-            '*on-error': 'BlockdevOnError' } }
+  'data': { 'device': 'str', '*base': 'str', '*backing-file': 'str',
+            '*speed': 'int', '*on-error': 'BlockdevOnError' } }
 
 ##
 # @block-job-set-speed:
diff --git a/qapi/event.json b/qapi/event.json
index ff97aeb377..c51dc491e0 100644
--- a/qapi/event.json
+++ b/qapi/event.json
@@ -288,12 +288,12 @@
 #
 # @sector-num: number of the first sector of the failed read operation
 #
-# @sector-count: failed read operation sector count
+# @sectors-count: failed read operation sector count
 #
 # Since: 2.0
 ##
 { 'event': 'QUORUM_FAILURE',
-  'data': { 'reference': 'str', 'sector-num': 'int', 'sector-count': 'int' } }
+  'data': { 'reference': 'str', 'sector-num': 'int', 'sectors-count': 'int' } }
 
 ##
 # @QUORUM_REPORT_BAD
@@ -309,13 +309,13 @@
 #
 # @sector-num: number of the first sector of the failed read operation
 #
-# @sector-count: failed read operation sector count
+# @sectors-count: failed read operation sector count
 #
 # Since: 2.0
 ##
 { 'event': 'QUORUM_REPORT_BAD',
   'data': { '*error': 'str', 'node-name': 'str',
-            'sector-num': 'int', 'sector-count': 'int' } }
+            'sector-num': 'int', 'sectors-count': 'int' } }
 
 ##
 # @VSERPORT_CHANGE
diff --git a/qemu-doc.texi b/qemu-doc.texi
index 88ec9bb133..ad92c85cba 100644
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -589,6 +589,22 @@ check -r all} is required, which may take some time.
 
 This option can only be enabled if @code{compat=1.1} is specified.
 
+@item nocow
+If this option is set to @code{on}, it will trun off COW of the file. It's only
+valid on btrfs, no effect on other file systems.
+
+Btrfs has low performance when hosting a VM image file, even more when the guest
+on the VM also using btrfs as file system. Turning off COW is a way to mitigate
+this bad performance. Generally there are two ways to turn off COW on btrfs:
+a) Disable it by mounting with nodatacow, then all newly created files will be
+NOCOW. b) For an empty file, add the NOCOW file attribute. That's what this option
+does.
+
+Note: this option is only valid to new or empty files. If there is an existing
+file which is COW and has data blocks already, it couldn't be changed to NOCOW
+by setting @code{nocow=on}. One can issue @code{lsattr filename} to check if
+the NOCOW flag is set or not (Capitabl 'C' is NOCOW flag).
+
 @end table
 
 @item qed
diff --git a/qemu-img.texi b/qemu-img.texi
index c68b54148a..8496f3b8dc 100644
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -474,6 +474,22 @@ check -r all} is required, which may take some time.
 
 This option can only be enabled if @code{compat=1.1} is specified.
 
+@item nocow
+If this option is set to @code{on}, it will trun off COW of the file. It's only
+valid on btrfs, no effect on other file systems.
+
+Btrfs has low performance when hosting a VM image file, even more when the guest
+on the VM also using btrfs as file system. Turning off COW is a way to mitigate
+this bad performance. Generally there are two ways to turn off COW on btrfs:
+a) Disable it by mounting with nodatacow, then all newly created files will be
+NOCOW. b) For an empty file, add the NOCOW file attribute. That's what this option
+does.
+
+Note: this option is only valid to new or empty files. If there is an existing
+file which is COW and has data blocks already, it couldn't be changed to NOCOW
+by setting @code{nocow=on}. One can issue @code{lsattr filename} to check if
+the NOCOW flag is set or not (Capitabl 'C' is NOCOW flag).
+
 @end table
 
 @item Other
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 1ea18b22a3..4be4765f27 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -979,13 +979,13 @@ EQMP
 
     {
         .name       = "block-stream",
-        .args_type  = "device:B,base:s?,speed:o?,on-error:s?",
+        .args_type  = "device:B,base:s?,speed:o?,backing-file:s?,on-error:s?",
         .mhandler.cmd_new = qmp_marshal_input_block_stream,
     },
 
     {
         .name       = "block-commit",
-        .args_type  = "device:B,base:s?,top:s,speed:o?",
+        .args_type  = "device:B,base:s?,top:s?,backing-file:s?,speed:o?",
         .mhandler.cmd_new = qmp_marshal_input_block_commit,
     },
 
@@ -1003,7 +1003,25 @@ Arguments:
           If not specified, this is the deepest backing image
           (json-string, optional)
 - "top":  The file name of the backing image within the image chain,
-          which contains the topmost data to be committed down.
+          which contains the topmost data to be committed down. If
+          not specified, this is the active layer. (json-string, optional)
+
+- backing-file:     The backing file string to write into the overlay
+                    image of 'top'.  If 'top' is the active layer,
+                    specifying a backing file string is an error. This
+                    filename is not validated.
+
+                    If a pathname string is such that it cannot be
+                    resolved by QEMU, that means that subsequent QMP or
+                    HMP commands must use node-names for the image in
+                    question, as filename lookup methods will fail.
+
+                    If not specified, QEMU will automatically determine
+                    the backing file string to use, or error out if
+                    there is no obvious choice. Care should be taken
+                    when specifying the string, to specify a valid
+                    filename or protocol.
+                    (json-string, optional) (Since 2.1)
 
           If top == base, that is an error.
           If top == active, the job will not be completed by itself,
@@ -1352,6 +1370,45 @@ Example:
 EQMP
 
     {
+        .name       = "change-backing-file",
+        .args_type  = "device:s,image-node-name:s,backing-file:s",
+        .mhandler.cmd_new = qmp_marshal_input_change_backing_file,
+    },
+
+SQMP
+change-backing-file
+-------------------
+Since: 2.1
+
+Change the backing file in the image file metadata.  This does not cause
+QEMU to reopen the image file to reparse the backing filename (it may,
+however, perform a reopen to change permissions from r/o -> r/w -> r/o,
+if needed). The new backing file string is written into the image file
+metadata, and the QEMU internal strings are updated.
+
+Arguments:
+
+- "image-node-name":    The name of the block driver state node of the
+                        image to modify.  The "device" is argument is used to
+                        verify "image-node-name" is in the chain described by
+                        "device".
+                        (json-string, optional)
+
+- "device":             The name of the device.
+                        (json-string)
+
+- "backing-file":       The string to write as the backing file.  This string is
+                        not validated, so care should be taken when specifying
+                        the string or the image chain may not be able to be
+                        reopened again.
+                        (json-string)
+
+Returns: Nothing on success
+         If "device" does not exist or cannot be determined, DeviceNotFound
+
+EQMP
+
+    {
         .name       = "balloon",
         .args_type  = "value:M",
         .mhandler.cmd_new = qmp_marshal_input_balloon,
diff --git a/tests/qemu-iotests-quick.sh b/tests/qemu-iotests-quick.sh
index c449e8ab4a..8a9a4c68e9 100755
--- a/tests/qemu-iotests-quick.sh
+++ b/tests/qemu-iotests-quick.sh
@@ -1,16 +1,6 @@
 #!/bin/sh
 
-# We don't know which of the system emulator binaries there is (or if there is
-# any at all), so the 'quick' group doesn't contain any tests that require
-# running qemu proper. Assign a fake binary name so that qemu-iotests doesn't
-# complain about the missing binary.
-export QEMU_PROG="this_should_be_unused"
-
-export QEMU_IMG_PROG="$(pwd)/qemu-img"
-export QEMU_IO_PROG="$(pwd)/qemu-io"
-export QEMU_NBD_PROG="$(pwd)/qemu-nbd"
-
-cd $SRC_PATH/tests/qemu-iotests
+cd tests/qemu-iotests
 
 ret=0
 ./check -T -nocache -qcow2 -g quick || ret=1
diff --git a/tests/qemu-iotests/040 b/tests/qemu-iotests/040
index d1668109dd..f1e16c11c7 100755
--- a/tests/qemu-iotests/040
+++ b/tests/qemu-iotests/040
@@ -35,11 +35,7 @@ test_img = os.path.join(iotests.test_dir, 'test.img')
 class ImageCommitTestCase(iotests.QMPTestCase):
     '''Abstract base class for image commit test cases'''
 
-    def run_commit_test(self, top, base, need_ready=False):
-        self.assert_no_active_block_jobs()
-        result = self.vm.qmp('block-commit', device='drive0', top=top, base=base)
-        self.assert_qmp(result, 'return', {})
-
+    def wait_for_complete(self, need_ready=False):
         completed = False
         ready = False
         while not completed:
@@ -62,6 +58,18 @@ class ImageCommitTestCase(iotests.QMPTestCase):
         self.assert_no_active_block_jobs()
         self.vm.shutdown()
 
+    def run_commit_test(self, top, base, need_ready=False):
+        self.assert_no_active_block_jobs()
+        result = self.vm.qmp('block-commit', device='drive0', top=top, base=base)
+        self.assert_qmp(result, 'return', {})
+        self.wait_for_complete(need_ready)
+
+    def run_default_commit_test(self):
+        self.assert_no_active_block_jobs()
+        result = self.vm.qmp('block-commit', device='drive0')
+        self.assert_qmp(result, 'return', {})
+        self.wait_for_complete()
+
 class TestSingleDrive(ImageCommitTestCase):
     image_len = 1 * 1024 * 1024
     test_len = 1 * 1024 * 256
@@ -113,17 +121,17 @@ class TestSingleDrive(ImageCommitTestCase):
         self.assertEqual(-1, qemu_io('-c', 'read -P 0xab 0 524288', backing_img).find("verification failed"))
         self.assertEqual(-1, qemu_io('-c', 'read -P 0xef 524288 524288', backing_img).find("verification failed"))
 
+    def test_top_is_default_active(self):
+        self.run_default_commit_test()
+        self.assertEqual(-1, qemu_io('-c', 'read -P 0xab 0 524288', backing_img).find("verification failed"))
+        self.assertEqual(-1, qemu_io('-c', 'read -P 0xef 524288 524288', backing_img).find("verification failed"))
+
     def test_top_and_base_reversed(self):
         self.assert_no_active_block_jobs()
         result = self.vm.qmp('block-commit', device='drive0', top='%s' % backing_img, base='%s' % mid_img)
         self.assert_qmp(result, 'error/class', 'GenericError')
         self.assert_qmp(result, 'error/desc', 'Base \'%s\' not found' % mid_img)
 
-    def test_top_omitted(self):
-        self.assert_no_active_block_jobs()
-        result = self.vm.qmp('block-commit', device='drive0')
-        self.assert_qmp(result, 'error/class', 'GenericError')
-        self.assert_qmp(result, 'error/desc', "Parameter 'top' is missing")
 
 class TestRelativePaths(ImageCommitTestCase):
     image_len = 1 * 1024 * 1024
diff --git a/tests/qemu-iotests/082.out b/tests/qemu-iotests/082.out
index 28309a0327..413e7ef391 100644
--- a/tests/qemu-iotests/082.out
+++ b/tests/qemu-iotests/082.out
@@ -66,6 +66,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: create -f qcow2 -o ? TEST_DIR/t.qcow2 128M
 Supported options:
@@ -77,6 +78,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: create -f qcow2 -o cluster_size=4k,help TEST_DIR/t.qcow2 128M
 Supported options:
@@ -88,6 +90,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: create -f qcow2 -o cluster_size=4k,? TEST_DIR/t.qcow2 128M
 Supported options:
@@ -99,6 +102,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: create -f qcow2 -o help,cluster_size=4k TEST_DIR/t.qcow2 128M
 Supported options:
@@ -110,6 +114,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: create -f qcow2 -o ?,cluster_size=4k TEST_DIR/t.qcow2 128M
 Supported options:
@@ -121,6 +126,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: create -f qcow2 -o cluster_size=4k -o help TEST_DIR/t.qcow2 128M
 Supported options:
@@ -132,6 +138,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: create -f qcow2 -o cluster_size=4k -o ? TEST_DIR/t.qcow2 128M
 Supported options:
@@ -143,6 +150,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: create -f qcow2 -o backing_file=TEST_DIR/t.qcow2,,help TEST_DIR/t.qcow2 128M
 Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=134217728 backing_file='TEST_DIR/t.qcow2,help' encryption=off cluster_size=65536 lazy_refcounts=off 
@@ -247,6 +255,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: convert -O qcow2 -o ? TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
 Supported options:
@@ -258,6 +267,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: convert -O qcow2 -o cluster_size=4k,help TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
 Supported options:
@@ -269,6 +279,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: convert -O qcow2 -o cluster_size=4k,? TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
 Supported options:
@@ -280,6 +291,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: convert -O qcow2 -o help,cluster_size=4k TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
 Supported options:
@@ -291,6 +303,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: convert -O qcow2 -o ?,cluster_size=4k TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
 Supported options:
@@ -302,6 +315,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: convert -O qcow2 -o cluster_size=4k -o help TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
 Supported options:
@@ -313,6 +327,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: convert -O qcow2 -o cluster_size=4k -o ? TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
 Supported options:
@@ -324,6 +339,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: convert -O qcow2 -o backing_file=TEST_DIR/t.qcow2,,help TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
 qemu-img: Could not open 'TEST_DIR/t.qcow2.base': Could not open backing file: Could not open 'TEST_DIR/t.qcow2,help': No such file or directory
@@ -417,6 +433,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: amend -f qcow2 -o ? TEST_DIR/t.qcow2
 Supported options:
@@ -428,6 +445,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: amend -f qcow2 -o cluster_size=4k,help TEST_DIR/t.qcow2
 Supported options:
@@ -439,6 +457,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: amend -f qcow2 -o cluster_size=4k,? TEST_DIR/t.qcow2
 Supported options:
@@ -450,6 +469,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: amend -f qcow2 -o help,cluster_size=4k TEST_DIR/t.qcow2
 Supported options:
@@ -461,6 +481,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: amend -f qcow2 -o ?,cluster_size=4k TEST_DIR/t.qcow2
 Supported options:
@@ -472,6 +493,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: amend -f qcow2 -o cluster_size=4k -o help TEST_DIR/t.qcow2
 Supported options:
@@ -483,6 +505,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: amend -f qcow2 -o cluster_size=4k -o ? TEST_DIR/t.qcow2
 Supported options:
@@ -494,6 +517,7 @@ encryption       Encrypt the image
 cluster_size     qcow2 cluster size
 preallocation    Preallocation mode (allowed values: off, metadata)
 lazy_refcounts   Postpone refcount updates
+nocow            Turn off copy-on-write (valid only on btrfs)
 
 Testing: amend -f qcow2 -o backing_file=TEST_DIR/t.qcow2,,help TEST_DIR/t.qcow2
 
diff --git a/tests/qemu-iotests/group b/tests/qemu-iotests/group
index e3dc4e8754..6e67f61262 100644
--- a/tests/qemu-iotests/group
+++ b/tests/qemu-iotests/group
@@ -7,16 +7,16 @@
 #
 # test-group association ... one line per test
 #
-001 rw auto
+001 rw auto quick
 002 rw auto quick
 003 rw auto
 004 rw auto quick
-005 img auto
+005 img auto quick
 006 img auto
 007 snapshot auto
-008 rw auto
-009 rw auto
-010 rw auto
+008 rw auto quick
+009 rw auto quick
+010 rw auto quick
 011 rw auto quick
 012 auto quick
 013 rw auto
@@ -24,36 +24,36 @@
 015 rw snapshot auto
 016 rw auto quick
 017 rw backing auto quick
-018 rw backing auto
+018 rw backing auto quick
 019 rw backing auto quick
 020 rw backing auto quick
-021 io auto
+021 io auto quick
 022 rw snapshot auto
 023 rw auto
 024 rw backing auto quick
 025 rw auto quick
 026 rw blkdbg auto
 027 rw auto quick
-028 rw backing auto
+028 rw backing auto quick
 029 rw auto quick
 030 rw auto backing
 031 rw auto quick
-032 rw auto
+032 rw auto quick
 033 rw auto quick
-034 rw auto backing
+034 rw auto backing quick
 035 rw auto quick
 036 rw auto quick
-037 rw auto backing
-038 rw auto backing
-039 rw auto
+037 rw auto backing quick
+038 rw auto backing quick
+039 rw auto quick
 040 rw auto
 041 rw auto backing
 042 rw auto quick
 043 rw auto backing
 044 rw auto
-045 rw auto
-046 rw auto aio
-047 rw auto
+045 rw auto quick
+046 rw auto aio quick
+047 rw auto quick
 048 img auto quick
 049 rw auto
 050 rw auto backing quick
@@ -71,32 +71,32 @@
 062 rw auto quick
 063 rw auto quick
 064 rw auto quick
-065 rw auto
+065 rw auto quick
 066 rw auto quick
-067 rw auto
-068 rw auto
+067 rw auto quick
+068 rw auto quick
 069 rw auto quick
 070 rw auto quick
-071 rw auto
+071 rw auto quick
 072 rw auto quick
 073 rw auto quick
 074 rw auto quick
-075 rw auto
+075 rw auto quick
 076 auto
 077 rw auto quick
-078 rw auto
+078 rw auto quick
 079 rw auto
 080 rw auto
-081 rw auto
+081 rw auto quick
 082 rw auto quick
 083 rw auto
-084 img auto
+084 img auto quick
 085 rw auto
 086 rw auto quick
-087 rw auto
-088 rw auto
+087 rw auto quick
+088 rw auto quick
 089 rw auto quick
 090 rw auto quick
-091 rw auto
+091 rw auto quick
 092 rw auto quick
-095 rw auto
+095 rw auto quick