Upgrade version to 5.2upstream/5.2.0sandbox/wangbiao/qemu_5.2

Change-Id: I79199e4f7e9f27b498cd41113833a6158d4f07a2
Signed-off-by: biao716.wang <biao716.wang@samsung.com>

1 files changed, 457 insertions, 140 deletions

diff --git a/block/commit.c b/block/commit.c
index 2227fc2e6..71db7ba74 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -12,10 +12,15 @@
  *
  */
 
+#include "qemu/osdep.h"
+#include "qemu/cutils.h"
 #include "trace.h"
 #include "block/block_int.h"
-#include "block/blockjob.h"
+#include "block/blockjob_int.h"
+#include "qapi/error.h"
+#include "qapi/qmp/qerror.h"
 #include "qemu/ratelimit.h"
+#include "sysemu/block-backend.h"
 
 enum {
     /*
@@ -26,233 +31,545 @@ enum {
     COMMIT_BUFFER_SIZE = 512 * 1024, /* in bytes */
 };
 
-#define SLICE_TIME 100000000ULL /* ns */
-
 typedef struct CommitBlockJob {
     BlockJob common;
-    RateLimit limit;
-    BlockDriverState *active;
-    BlockDriverState *top;
-    BlockDriverState *base;
+    BlockDriverState *commit_top_bs;
+    BlockBackend *top;
+    BlockBackend *base;
+    BlockDriverState *base_bs;
+    BlockDriverState *base_overlay;
     BlockdevOnError on_error;
-    int base_flags;
-    int orig_overlay_flags;
+    bool base_read_only;
+    bool chain_frozen;
+    char *backing_file_str;
 } CommitBlockJob;
 
-static int coroutine_fn commit_populate(BlockDriverState *bs,
-                                        BlockDriverState *base,
-                                        int64_t sector_num, int nb_sectors,
-                                        void *buf)
+static int commit_prepare(Job *job)
 {
-    int ret = 0;
+    CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
+
+    bdrv_unfreeze_backing_chain(s->commit_top_bs, s->base_bs);
+    s->chain_frozen = false;
 
-    ret = bdrv_read(bs, sector_num, buf, nb_sectors);
-    if (ret) {
-        return ret;
+    /* Remove base node parent that still uses BLK_PERM_WRITE/RESIZE before
+     * the normal backing chain can be restored. */
+    blk_unref(s->base);
+    s->base = NULL;
+
+    /* FIXME: bdrv_drop_intermediate treats total failures and partial failures
+     * identically. Further work is needed to disambiguate these cases. */
+    return bdrv_drop_intermediate(s->commit_top_bs, s->base_bs,
+                                  s->backing_file_str);
+}
+
+static void commit_abort(Job *job)
+{
+    CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
+    BlockDriverState *top_bs = blk_bs(s->top);
+
+    if (s->chain_frozen) {
+        bdrv_unfreeze_backing_chain(s->commit_top_bs, s->base_bs);
     }
 
-    ret = bdrv_write(base, sector_num, buf, nb_sectors);
-    if (ret) {
-        return ret;
+    /* Make sure commit_top_bs and top stay around until bdrv_replace_node() */
+    bdrv_ref(top_bs);
+    bdrv_ref(s->commit_top_bs);
+
+    if (s->base) {
+        blk_unref(s->base);
     }
 
-    return 0;
+    /* free the blockers on the intermediate nodes so that bdrv_replace_nodes
+     * can succeed */
+    block_job_remove_all_bdrv(&s->common);
+
+    /* If bdrv_drop_intermediate() failed (or was not invoked), remove the
+     * commit filter driver from the backing chain now. Do this as the final
+     * step so that the 'consistent read' permission can be granted.
+     *
+     * XXX Can (or should) we somehow keep 'consistent read' blocked even
+     * after the failed/cancelled commit job is gone? If we already wrote
+     * something to base, the intermediate images aren't valid any more. */
+    bdrv_replace_node(s->commit_top_bs, s->commit_top_bs->backing->bs,
+                      &error_abort);
+
+    bdrv_unref(s->commit_top_bs);
+    bdrv_unref(top_bs);
 }
 
-static void coroutine_fn commit_run(void *opaque)
+static void commit_clean(Job *job)
 {
-    CommitBlockJob *s = opaque;
-    BlockDriverState *active = s->active;
-    BlockDriverState *top = s->top;
-    BlockDriverState *base = s->base;
-    BlockDriverState *overlay_bs;
-    int64_t sector_num, end;
-    int ret = 0;
-    int n = 0;
-    void *buf;
-    int bytes_written = 0;
-    int64_t base_len;
+    CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
 
-    ret = s->common.len = bdrv_getlength(top);
+    /* restore base open flags here if appropriate (e.g., change the base back
+     * to r/o). These reopens do not need to be atomic, since we won't abort
+     * even on failure here */
+    if (s->base_read_only) {
+        bdrv_reopen_set_read_only(s->base_bs, true, NULL);
+    }
 
+    g_free(s->backing_file_str);
+    blk_unref(s->top);
+}
 
-    if (s->common.len < 0) {
-        goto exit_restore_reopen;
+static int coroutine_fn commit_run(Job *job, Error **errp)
+{
+    CommitBlockJob *s = container_of(job, CommitBlockJob, common.job);
+    int64_t offset;
+    uint64_t delay_ns = 0;
+    int ret = 0;
+    int64_t n = 0; /* bytes */
+    void *buf = NULL;
+    int64_t len, base_len;
+
+    ret = len = blk_getlength(s->top);
+    if (len < 0) {
+        goto out;
     }
+    job_progress_set_remaining(&s->common.job, len);
 
-    ret = base_len = bdrv_getlength(base);
+    ret = base_len = blk_getlength(s->base);
     if (base_len < 0) {
-        goto exit_restore_reopen;
+        goto out;
     }
 
-    if (base_len < s->common.len) {
-        ret = bdrv_truncate(base, s->common.len);
+    if (base_len < len) {
+        ret = blk_truncate(s->base, len, false, PREALLOC_MODE_OFF, 0, NULL);
         if (ret) {
-            goto exit_restore_reopen;
+            goto out;
         }
     }
 
-    end = s->common.len >> BDRV_SECTOR_BITS;
-    buf = qemu_blockalign(top, COMMIT_BUFFER_SIZE);
+    buf = blk_blockalign(s->top, COMMIT_BUFFER_SIZE);
 
-    for (sector_num = 0; sector_num < end; sector_num += n) {
-        uint64_t delay_ns = 0;
+    for (offset = 0; offset < len; offset += n) {
         bool copy;
+        bool error_in_source = true;
 
-wait:
         /* Note that even when no rate limit is applied we need to yield
          * with no pending I/O here so that bdrv_drain_all() returns.
          */
-        block_job_sleep_ns(&s->common, rt_clock, delay_ns);
-        if (block_job_is_cancelled(&s->common)) {
+        job_sleep_ns(&s->common.job, delay_ns);
+        if (job_is_cancelled(&s->common.job)) {
             break;
         }
         /* Copy if allocated above the base */
-        ret = bdrv_co_is_allocated_above(top, base, sector_num,
-                                         COMMIT_BUFFER_SIZE / BDRV_SECTOR_SIZE,
-                                         &n);
-        copy = (ret == 1);
-        trace_commit_one_iteration(s, sector_num, n, ret);
+        ret = bdrv_is_allocated_above(blk_bs(s->top), s->base_overlay, true,
+                                      offset, COMMIT_BUFFER_SIZE, &n);
+        copy = (ret > 0);
+        trace_commit_one_iteration(s, offset, n, ret);
         if (copy) {
-            if (s->common.speed) {
-                delay_ns = ratelimit_calculate_delay(&s->limit, n);
-                if (delay_ns > 0) {
-                    goto wait;
+            assert(n < SIZE_MAX);
+
+            ret = blk_co_pread(s->top, offset, n, buf, 0);
+            if (ret >= 0) {
+                ret = blk_co_pwrite(s->base, offset, n, buf, 0);
+                if (ret < 0) {
+                    error_in_source = false;
                 }
             }
-            ret = commit_populate(top, base, sector_num, n, buf);
-            bytes_written += n * BDRV_SECTOR_SIZE;
         }
         if (ret < 0) {
-            if (s->on_error == BLOCKDEV_ON_ERROR_STOP ||
-                s->on_error == BLOCKDEV_ON_ERROR_REPORT||
-                (s->on_error == BLOCKDEV_ON_ERROR_ENOSPC && ret == -ENOSPC)) {
-                goto exit_free_buf;
+            BlockErrorAction action =
+                block_job_error_action(&s->common, s->on_error,
+                                       error_in_source, -ret);
+            if (action == BLOCK_ERROR_ACTION_REPORT) {
+                goto out;
             } else {
                 n = 0;
                 continue;
             }
         }
         /* Publish progress */
-        s->common.offset += n * BDRV_SECTOR_SIZE;
+        job_progress_update(&s->common.job, n);
+
+        if (copy) {
+            delay_ns = block_job_ratelimit_get_delay(&s->common, n);
+        } else {
+            delay_ns = 0;
+        }
     }
 
     ret = 0;
 
-    if (!block_job_is_cancelled(&s->common) && sector_num == end) {
-        /* success */
-        ret = bdrv_drop_intermediate(active, top, base);
-    }
-
-exit_free_buf:
+out:
     qemu_vfree(buf);
 
-exit_restore_reopen:
-    /* restore base open flags here if appropriate (e.g., change the base back
-     * to r/o). These reopens do not need to be atomic, since we won't abort
-     * even on failure here */
-    if (s->base_flags != bdrv_get_flags(base)) {
-        bdrv_reopen(base, s->base_flags, NULL);
-    }
-    overlay_bs = bdrv_find_overlay(active, top);
-    if (overlay_bs && s->orig_overlay_flags != bdrv_get_flags(overlay_bs)) {
-        bdrv_reopen(overlay_bs, s->orig_overlay_flags, NULL);
-    }
+    return ret;
+}
+
+static const BlockJobDriver commit_job_driver = {
+    .job_driver = {
+        .instance_size = sizeof(CommitBlockJob),
+        .job_type      = JOB_TYPE_COMMIT,
+        .free          = block_job_free,
+        .user_resume   = block_job_user_resume,
+        .run           = commit_run,
+        .prepare       = commit_prepare,
+        .abort         = commit_abort,
+        .clean         = commit_clean
+    },
+};
 
-    block_job_completed(&s->common, ret);
+static int coroutine_fn bdrv_commit_top_preadv(BlockDriverState *bs,
+    uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags)
+{
+    return bdrv_co_preadv(bs->backing, offset, bytes, qiov, flags);
 }
 
-static void commit_set_speed(BlockJob *job, int64_t speed, Error **errp)
+static void bdrv_commit_top_refresh_filename(BlockDriverState *bs)
 {
-    CommitBlockJob *s = container_of(job, CommitBlockJob, common);
+    pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
+            bs->backing->bs->filename);
+}
 
-    if (speed < 0) {
-        error_set(errp, QERR_INVALID_PARAMETER, "speed");
-        return;
-    }
-    ratelimit_set_speed(&s->limit, speed / BDRV_SECTOR_SIZE, SLICE_TIME);
+static void bdrv_commit_top_child_perm(BlockDriverState *bs, BdrvChild *c,
+                                       BdrvChildRole role,
+                                       BlockReopenQueue *reopen_queue,
+                                       uint64_t perm, uint64_t shared,
+                                       uint64_t *nperm, uint64_t *nshared)
+{
+    *nperm = 0;
+    *nshared = BLK_PERM_ALL;
 }
 
-static const BlockJobType commit_job_type = {
-    .instance_size = sizeof(CommitBlockJob),
-    .job_type      = "commit",
-    .set_speed     = commit_set_speed,
+/* Dummy node that provides consistent read to its users without requiring it
+ * from its backing file and that allows writes on the backing file chain. */
+static BlockDriver bdrv_commit_top = {
+    .format_name                = "commit_top",
+    .bdrv_co_preadv             = bdrv_commit_top_preadv,
+    .bdrv_refresh_filename      = bdrv_commit_top_refresh_filename,
+    .bdrv_child_perm            = bdrv_commit_top_child_perm,
+
+    .is_filter                  = true,
 };
 
-void commit_start(BlockDriverState *bs, BlockDriverState *base,
-                  BlockDriverState *top, int64_t speed,
-                  BlockdevOnError on_error, BlockDriverCompletionFunc *cb,
-                  void *opaque, Error **errp)
+void commit_start(const char *job_id, BlockDriverState *bs,
+                  BlockDriverState *base, BlockDriverState *top,
+                  int creation_flags, int64_t speed,
+                  BlockdevOnError on_error, const char *backing_file_str,
+                  const char *filter_node_name, Error **errp)
 {
     CommitBlockJob *s;
-    BlockReopenQueue *reopen_queue = NULL;
-    int orig_overlay_flags;
-    int orig_base_flags;
-    BlockDriverState *overlay_bs;
+    BlockDriverState *iter;
+    BlockDriverState *commit_top_bs = NULL;
+    BlockDriverState *filtered_base;
     Error *local_err = NULL;
+    int64_t base_size, top_size;
+    uint64_t base_perms, iter_shared_perms;
+    int ret;
 
-    if ((on_error == BLOCKDEV_ON_ERROR_STOP ||
-         on_error == BLOCKDEV_ON_ERROR_ENOSPC) &&
-        !bdrv_iostatus_is_enabled(bs)) {
-        error_set(errp, QERR_INVALID_PARAMETER_COMBINATION);
+    assert(top != bs);
+    if (bdrv_skip_filters(top) == bdrv_skip_filters(base)) {
+        error_setg(errp, "Invalid files for merge: top and base are the same");
         return;
     }
 
-    /* Once we support top == active layer, remove this check */
-    if (top == bs) {
-        error_setg(errp,
-                   "Top image as the active layer is currently unsupported");
+    base_size = bdrv_getlength(base);
+    if (base_size < 0) {
+        error_setg_errno(errp, -base_size, "Could not inquire base image size");
         return;
     }
 
-    if (top == base) {
-        error_setg(errp, "Invalid files for merge: top and base are the same");
+    top_size = bdrv_getlength(top);
+    if (top_size < 0) {
+        error_setg_errno(errp, -top_size, "Could not inquire top image size");
         return;
     }
 
-    overlay_bs = bdrv_find_overlay(bs, top);
+    base_perms = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE;
+    if (base_size < top_size) {
+        base_perms |= BLK_PERM_RESIZE;
+    }
 
-    if (overlay_bs == NULL) {
-        error_setg(errp, "Could not find overlay image for %s:", top->filename);
+    s = block_job_create(job_id, &commit_job_driver, NULL, bs, 0, BLK_PERM_ALL,
+                         speed, creation_flags, NULL, NULL, errp);
+    if (!s) {
         return;
     }
 
-    orig_base_flags    = bdrv_get_flags(base);
-    orig_overlay_flags = bdrv_get_flags(overlay_bs);
+    /* convert base to r/w, if necessary */
+    s->base_read_only = bdrv_is_read_only(base);
+    if (s->base_read_only) {
+        if (bdrv_reopen_set_read_only(base, false, errp) != 0) {
+            goto fail;
+        }
+    }
 
-    /* convert base & overlay_bs to r/w, if necessary */
-    if (!(orig_base_flags & BDRV_O_RDWR)) {
-        reopen_queue = bdrv_reopen_queue(reopen_queue, base,
-                                         orig_base_flags | BDRV_O_RDWR);
+    /* Insert commit_top block node above top, so we can block consistent read
+     * on the backing chain below it */
+    commit_top_bs = bdrv_new_open_driver(&bdrv_commit_top, filter_node_name, 0,
+                                         errp);
+    if (commit_top_bs == NULL) {
+        goto fail;
     }
-    if (!(orig_overlay_flags & BDRV_O_RDWR)) {
-        reopen_queue = bdrv_reopen_queue(reopen_queue, overlay_bs,
-                                         orig_overlay_flags | BDRV_O_RDWR);
+    if (!filter_node_name) {
+        commit_top_bs->implicit = true;
     }
-    if (reopen_queue) {
-        bdrv_reopen_multiple(reopen_queue, &local_err);
-        if (local_err != NULL) {
-            error_propagate(errp, local_err);
-            return;
-        }
+
+    /* So that we can always drop this node */
+    commit_top_bs->never_freeze = true;
+
+    commit_top_bs->total_sectors = top->total_sectors;
+
+    bdrv_append(commit_top_bs, top, &local_err);
+    if (local_err) {
+        commit_top_bs = NULL;
+        error_propagate(errp, local_err);
+        goto fail;
     }
 
+    s->commit_top_bs = commit_top_bs;
 
-    s = block_job_create(&commit_job_type, bs, speed, cb, opaque, errp);
-    if (!s) {
-        return;
+    /*
+     * Block all nodes between top and base, because they will
+     * disappear from the chain after this operation.
+     * Note that this assumes that the user is fine with removing all
+     * nodes (including R/W filters) between top and base.  Assuring
+     * this is the responsibility of the interface (i.e. whoever calls
+     * commit_start()).
+     */
+    s->base_overlay = bdrv_find_overlay(top, base);
+    assert(s->base_overlay);
+
+    /*
+     * The topmost node with
+     * bdrv_skip_filters(filtered_base) == bdrv_skip_filters(base)
+     */
+    filtered_base = bdrv_cow_bs(s->base_overlay);
+    assert(bdrv_skip_filters(filtered_base) == bdrv_skip_filters(base));
+
+    /*
+     * XXX BLK_PERM_WRITE needs to be allowed so we don't block ourselves
+     * at s->base (if writes are blocked for a node, they are also blocked
+     * for its backing file). The other options would be a second filter
+     * driver above s->base.
+     */
+    iter_shared_perms = BLK_PERM_WRITE_UNCHANGED | BLK_PERM_WRITE;
+
+    for (iter = top; iter != base; iter = bdrv_filter_or_cow_bs(iter)) {
+        if (iter == filtered_base) {
+            /*
+             * From here on, all nodes are filters on the base.  This
+             * allows us to share BLK_PERM_CONSISTENT_READ.
+             */
+            iter_shared_perms |= BLK_PERM_CONSISTENT_READ;
+        }
+
+        ret = block_job_add_bdrv(&s->common, "intermediate node", iter, 0,
+                                 iter_shared_perms, errp);
+        if (ret < 0) {
+            goto fail;
+        }
     }
 
-    s->base   = base;
-    s->top    = top;
-    s->active = bs;
+    if (bdrv_freeze_backing_chain(commit_top_bs, base, errp) < 0) {
+        goto fail;
+    }
+    s->chain_frozen = true;
 
-    s->base_flags          = orig_base_flags;
-    s->orig_overlay_flags  = orig_overlay_flags;
+    ret = block_job_add_bdrv(&s->common, "base", base, 0, BLK_PERM_ALL, errp);
+    if (ret < 0) {
+        goto fail;
+    }
 
+    s->base = blk_new(s->common.job.aio_context,
+                      base_perms,
+                      BLK_PERM_CONSISTENT_READ
+                      | BLK_PERM_GRAPH_MOD
+                      | BLK_PERM_WRITE_UNCHANGED);
+    ret = blk_insert_bs(s->base, base, errp);
+    if (ret < 0) {
+        goto fail;
+    }
+    blk_set_disable_request_queuing(s->base, true);
+    s->base_bs = base;
+
+    /* Required permissions are already taken with block_job_add_bdrv() */
+    s->top = blk_new(s->common.job.aio_context, 0, BLK_PERM_ALL);
+    ret = blk_insert_bs(s->top, top, errp);
+    if (ret < 0) {
+        goto fail;
+    }
+    blk_set_disable_request_queuing(s->top, true);
+
+    s->backing_file_str = g_strdup(backing_file_str);
     s->on_error = on_error;
-    s->common.co = qemu_coroutine_create(commit_run);
 
-    trace_commit_start(bs, base, top, s, s->common.co, opaque);
-    qemu_coroutine_enter(s->common.co, s);
+    trace_commit_start(bs, base, top, s);
+    job_start(&s->common.job);
+    return;
+
+fail:
+    if (s->chain_frozen) {
+        bdrv_unfreeze_backing_chain(commit_top_bs, base);
+    }
+    if (s->base) {
+        blk_unref(s->base);
+    }
+    if (s->top) {
+        blk_unref(s->top);
+    }
+    if (s->base_read_only) {
+        bdrv_reopen_set_read_only(base, true, NULL);
+    }
+    job_early_fail(&s->common.job);
+    /* commit_top_bs has to be replaced after deleting the block job,
+     * otherwise this would fail because of lack of permissions. */
+    if (commit_top_bs) {
+        bdrv_replace_node(commit_top_bs, top, &error_abort);
+    }
+}
+
+
+#define COMMIT_BUF_SIZE (2048 * BDRV_SECTOR_SIZE)
+
+/* commit COW file into the raw image */
+int bdrv_commit(BlockDriverState *bs)
+{
+    BlockBackend *src, *backing;
+    BlockDriverState *backing_file_bs = NULL;
+    BlockDriverState *commit_top_bs = NULL;
+    BlockDriver *drv = bs->drv;
+    AioContext *ctx;
+    int64_t offset, length, backing_length;
+    int ro;
+    int64_t n;
+    int ret = 0;
+    uint8_t *buf = NULL;
+    Error *local_err = NULL;
+
+    if (!drv)
+        return -ENOMEDIUM;
+
+    backing_file_bs = bdrv_cow_bs(bs);
+
+    if (!backing_file_bs) {
+        return -ENOTSUP;
+    }
+
+    if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_COMMIT_SOURCE, NULL) ||
+        bdrv_op_is_blocked(backing_file_bs, BLOCK_OP_TYPE_COMMIT_TARGET, NULL))
+    {
+        return -EBUSY;
+    }
+
+    ro = backing_file_bs->read_only;
+
+    if (ro) {
+        if (bdrv_reopen_set_read_only(backing_file_bs, false, NULL)) {
+            return -EACCES;
+        }
+    }
+
+    ctx = bdrv_get_aio_context(bs);
+    /* WRITE_UNCHANGED is required for bdrv_make_empty() */
+    src = blk_new(ctx, BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED,
+                  BLK_PERM_ALL);
+    backing = blk_new(ctx, BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL);
+
+    ret = blk_insert_bs(src, bs, &local_err);
+    if (ret < 0) {
+        error_report_err(local_err);
+        goto ro_cleanup;
+    }
+
+    /* Insert commit_top block node above backing, so we can write to it */
+    commit_top_bs = bdrv_new_open_driver(&bdrv_commit_top, NULL, BDRV_O_RDWR,
+                                         &local_err);
+    if (commit_top_bs == NULL) {
+        error_report_err(local_err);
+        goto ro_cleanup;
+    }
+
+    bdrv_set_backing_hd(commit_top_bs, backing_file_bs, &error_abort);
+    bdrv_set_backing_hd(bs, commit_top_bs, &error_abort);
+
+    ret = blk_insert_bs(backing, backing_file_bs, &local_err);
+    if (ret < 0) {
+        error_report_err(local_err);
+        goto ro_cleanup;
+    }
+
+    length = blk_getlength(src);
+    if (length < 0) {
+        ret = length;
+        goto ro_cleanup;
+    }
+
+    backing_length = blk_getlength(backing);
+    if (backing_length < 0) {
+        ret = backing_length;
+        goto ro_cleanup;
+    }
+
+    /* If our top snapshot is larger than the backing file image,
+     * grow the backing file image if possible.  If not possible,
+     * we must return an error */
+    if (length > backing_length) {
+        ret = blk_truncate(backing, length, false, PREALLOC_MODE_OFF, 0,
+                           &local_err);
+        if (ret < 0) {
+            error_report_err(local_err);
+            goto ro_cleanup;
+        }
+    }
+
+    /* blk_try_blockalign() for src will choose an alignment that works for
+     * backing as well, so no need to compare the alignment manually. */
+    buf = blk_try_blockalign(src, COMMIT_BUF_SIZE);
+    if (buf == NULL) {
+        ret = -ENOMEM;
+        goto ro_cleanup;
+    }
+
+    for (offset = 0; offset < length; offset += n) {
+        ret = bdrv_is_allocated(bs, offset, COMMIT_BUF_SIZE, &n);
+        if (ret < 0) {
+            goto ro_cleanup;
+        }
+        if (ret) {
+            ret = blk_pread(src, offset, buf, n);
+            if (ret < 0) {
+                goto ro_cleanup;
+            }
+
+            ret = blk_pwrite(backing, offset, buf, n, 0);
+            if (ret < 0) {
+                goto ro_cleanup;
+            }
+        }
+    }
+
+    ret = blk_make_empty(src, NULL);
+    /* Ignore -ENOTSUP */
+    if (ret < 0 && ret != -ENOTSUP) {
+        goto ro_cleanup;
+    }
+
+    blk_flush(src);
+
+    /*
+     * Make sure all data we wrote to the backing device is actually
+     * stable on disk.
+     */
+    blk_flush(backing);
+
+    ret = 0;
+ro_cleanup:
+    qemu_vfree(buf);
+
+    blk_unref(backing);
+    if (bdrv_cow_bs(bs) != backing_file_bs) {
+        bdrv_set_backing_hd(bs, backing_file_bs, &error_abort);
+    }
+    bdrv_unref(commit_top_bs);
+    blk_unref(src);
+
+    if (ro) {
+        /* ignoring error return here */
+        bdrv_reopen_set_read_only(backing_file_bs, true, NULL);
+    }
+
+    return ret;
 }