block/stream.c - third_party/qemu - Git at Google

 /*
  * Image streaming
  *
  * Copyright IBM, Corp. 2011
  *
  * Authors:
  *  Stefan Hajnoczi   <stefanha@linux.vnet.ibm.com>
  *
  * This work is licensed under the terms of the GNU LGPL, version 2 or later.
  * See the COPYING.LIB file in the top-level directory.
  *
  */

 #include "qemu/osdep.h"
 #include "trace.h"
 #include "block/block_int.h"
 #include "block/blockjob_int.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qdict.h"
 #include "qemu/ratelimit.h"
 #include "sysemu/block-backend.h"
 #include "block/copy-on-read.h"

 enum {
     /*
      * Maximum chunk size to feed to copy-on-read.  This should be
      * large enough to process multiple clusters in a single call, so
      * that populating contiguous regions of the image is efficient.
      */
     STREAM_CHUNK = 512 * 1024, /* in bytes */
 };

 typedef struct StreamBlockJob {
     BlockJob common;
     BlockBackend *blk;
     BlockDriverState *base_overlay; /* COW overlay (stream from this) */
     BlockDriverState *above_base;   /* Node directly above the base */
     BlockDriverState *cor_filter_bs;
     BlockDriverState *target_bs;
     BlockdevOnError on_error;
     char *backing_file_str;
     bool backing_mask_protocol;
     bool bs_read_only;
 } StreamBlockJob;

 static int coroutine_fn stream_populate(BlockBackend *blk,
                                         int64_t offset, uint64_t bytes)
 {
     assert(bytes < SIZE_MAX);

     return blk_co_preadv(blk, offset, bytes, NULL, BDRV_REQ_PREFETCH);
 }

 static int stream_prepare(Job *job)
 {
     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
     BlockDriverState *unfiltered_bs;
     BlockDriverState *unfiltered_bs_cow;
     BlockDriverState *base;
     BlockDriverState *unfiltered_base;
     Error *local_err = NULL;
     int ret = 0;

     GLOBAL_STATE_CODE();

     bdrv_graph_rdlock_main_loop();
     unfiltered_bs = bdrv_skip_filters(s->target_bs);
     unfiltered_bs_cow = bdrv_cow_bs(unfiltered_bs);
     bdrv_graph_rdunlock_main_loop();

     /* We should drop filter at this point, as filter hold the backing chain */
     bdrv_cor_filter_drop(s->cor_filter_bs);
     s->cor_filter_bs = NULL;

     /*
      * bdrv_set_backing_hd() requires that the unfiltered_bs and the COW child
      * of unfiltered_bs is drained. Drain already here and use
      * bdrv_set_backing_hd_drained() instead because the polling during
      * drained_begin() might change the graph, and if we do this only later, we
      * may end up working with the wrong base node (or it might even have gone
      * away by the time we want to use it).
      */
     bdrv_drained_begin(unfiltered_bs);
     if (unfiltered_bs_cow) {
         bdrv_ref(unfiltered_bs_cow);
         bdrv_drained_begin(unfiltered_bs_cow);
     }

     bdrv_graph_rdlock_main_loop();
     base = bdrv_filter_or_cow_bs(s->above_base);
     unfiltered_base = bdrv_skip_filters(base);
     bdrv_graph_rdunlock_main_loop();

     if (unfiltered_bs_cow) {
         const char *base_id = NULL, *base_fmt = NULL;
         if (unfiltered_base) {
             base_id = s->backing_file_str ?: unfiltered_base->filename;
             if (unfiltered_base->drv) {
                 if (s->backing_mask_protocol &&
                     unfiltered_base->drv->protocol_name) {
                     base_fmt = "raw";
                 } else {
                     base_fmt = unfiltered_base->drv->format_name;
                 }
             }
         }

         bdrv_graph_wrlock();
         bdrv_set_backing_hd_drained(unfiltered_bs, base, &local_err);
         bdrv_graph_wrunlock();

         /*
          * This call will do I/O, so the graph can change again from here on.
          * We have already completed the graph change, so we are not in danger
          * of operating on the wrong node any more if this happens.
          */
         ret = bdrv_change_backing_file(unfiltered_bs, base_id, base_fmt, false);
         if (local_err) {
             error_report_err(local_err);
             ret = -EPERM;
             goto out;
         }
     }

 out:
     if (unfiltered_bs_cow) {
         bdrv_drained_end(unfiltered_bs_cow);
         bdrv_unref(unfiltered_bs_cow);
     }
     bdrv_drained_end(unfiltered_bs);
     return ret;
 }

 static void stream_clean(Job *job)
 {
     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);

     if (s->cor_filter_bs) {
         bdrv_cor_filter_drop(s->cor_filter_bs);
         s->cor_filter_bs = NULL;
     }

     blk_unref(s->blk);
     s->blk = NULL;

     /* Reopen the image back in read-only mode if necessary */
     if (s->bs_read_only) {
         /* Give up write permissions before making it read-only */
         bdrv_reopen_set_read_only(s->target_bs, true, NULL);
     }

     g_free(s->backing_file_str);
 }

 static int coroutine_fn stream_run(Job *job, Error **errp)
 {
     StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
     BlockDriverState *unfiltered_bs;
     int64_t len;
     int64_t offset = 0;
     int error = 0;
     int64_t n = 0; /* bytes */

     WITH_GRAPH_RDLOCK_GUARD() {
         unfiltered_bs = bdrv_skip_filters(s->target_bs);
         if (unfiltered_bs == s->base_overlay) {
             /* Nothing to stream */
             return 0;
         }

         len = bdrv_co_getlength(s->target_bs);
         if (len < 0) {
             return len;
         }
     }
     job_progress_set_remaining(&s->common.job, len);

     for ( ; offset < len; offset += n) {
         bool copy;
         int ret;

         /* 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_ratelimit_sleep(&s->common);
         if (job_is_cancelled(&s->common.job)) {
             break;
         }

         copy = false;

         WITH_GRAPH_RDLOCK_GUARD() {
             ret = bdrv_co_is_allocated(unfiltered_bs, offset, STREAM_CHUNK, &n);
             if (ret == 1) {
                 /* Allocated in the top, no need to copy.  */
             } else if (ret >= 0) {
                 /*
                  * Copy if allocated in the intermediate images.  Limit to the
                  * known-unallocated area [offset, offset+n*BDRV_SECTOR_SIZE).
                  */
                 ret = bdrv_co_is_allocated_above(bdrv_cow_bs(unfiltered_bs),
                                                  s->base_overlay, true,
                                                  offset, n, &n);
                 /* Finish early if end of backing file has been reached */
                 if (ret == 0 && n == 0) {
                     n = len - offset;
                 }

                 copy = (ret > 0);
             }
         }
         trace_stream_one_iteration(s, offset, n, ret);
         if (copy) {
             ret = stream_populate(s->blk, offset, n);
         }
         if (ret < 0) {
             BlockErrorAction action =
                 block_job_error_action(&s->common, s->on_error, true, -ret);
             if (action == BLOCK_ERROR_ACTION_STOP) {
                 n = 0;
                 continue;
             }
             if (error == 0) {
                 error = ret;
             }
             if (action == BLOCK_ERROR_ACTION_REPORT) {
                 break;
             }
         }

         /* Publish progress */
         job_progress_update(&s->common.job, n);
         if (copy) {
             block_job_ratelimit_processed_bytes(&s->common, n);
         }
     }

     /* Do not remove the backing file if an error was there but ignored. */
     return error;
 }

 static const BlockJobDriver stream_job_driver = {
     .job_driver = {
         .instance_size = sizeof(StreamBlockJob),
         .job_type      = JOB_TYPE_STREAM,
         .free          = block_job_free,
         .run           = stream_run,
         .prepare       = stream_prepare,
         .clean         = stream_clean,
         .user_resume   = block_job_user_resume,
     },
 };

 void stream_start(const char *job_id, BlockDriverState *bs,
                   BlockDriverState *base, const char *backing_file_str,
                   bool backing_mask_protocol,
                   BlockDriverState *bottom,
                   int creation_flags, int64_t speed,
                   BlockdevOnError on_error,
                   const char *filter_node_name,
                   Error **errp)
 {
     StreamBlockJob *s = NULL;
     BlockDriverState *iter;
     bool bs_read_only;
     int basic_flags = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED;
     BlockDriverState *base_overlay;
     BlockDriverState *cor_filter_bs = NULL;
     BlockDriverState *above_base;
     QDict *opts;
     int ret;

     GLOBAL_STATE_CODE();

     assert(!(base && bottom));
     assert(!(backing_file_str && bottom));

     bdrv_graph_rdlock_main_loop();

     if (bottom) {
         /*
          * New simple interface. The code is written in terms of old interface
          * with @base parameter (still, it doesn't freeze link to base, so in
          * this mean old code is correct for new interface). So, for now, just
          * emulate base_overlay and above_base. Still, when old interface
          * finally removed, we should refactor code to use only "bottom", but
          * not "*base*" things.
          */
         assert(!bottom->drv->is_filter);
         base_overlay = above_base = bottom;
     } else {
         base_overlay = bdrv_find_overlay(bs, base);
         if (!base_overlay) {
             error_setg(errp, "'%s' is not in the backing chain of '%s'",
                        base->node_name, bs->node_name);
             goto out_rdlock;
         }

         /*
          * Find the node directly above @base.  @base_overlay is a COW overlay,
          * so it must have a bdrv_cow_child(), but it is the immediate overlay
          * of @base, so between the two there can only be filters.
          */
         above_base = base_overlay;
         if (bdrv_cow_bs(above_base) != base) {
             above_base = bdrv_cow_bs(above_base);
             while (bdrv_filter_bs(above_base) != base) {
                 above_base = bdrv_filter_bs(above_base);
             }
         }
     }

     /* Make sure that the image is opened in read-write mode */
     bs_read_only = bdrv_is_read_only(bs);
     if (bs_read_only) {
         /* Hold the chain during reopen */
         if (bdrv_freeze_backing_chain(bs, above_base, errp) < 0) {
             goto out_rdlock;
         }

         ret = bdrv_reopen_set_read_only(bs, false, errp);

         /* failure, or cor-filter will hold the chain */
         bdrv_unfreeze_backing_chain(bs, above_base);

         if (ret < 0) {
             goto out_rdlock;
         }
     }

     bdrv_graph_rdunlock_main_loop();

     opts = qdict_new();

     qdict_put_str(opts, "driver", "copy-on-read");
     qdict_put_str(opts, "file", bdrv_get_node_name(bs));
     /* Pass the base_overlay node name as 'bottom' to COR driver */
     qdict_put_str(opts, "bottom", base_overlay->node_name);
     if (filter_node_name) {
         qdict_put_str(opts, "node-name", filter_node_name);
     }

     cor_filter_bs = bdrv_insert_node(bs, opts, BDRV_O_RDWR, errp);
     if (!cor_filter_bs) {
         goto fail;
     }

     if (!filter_node_name) {
         cor_filter_bs->implicit = true;
     }

     s = block_job_create(job_id, &stream_job_driver, NULL, cor_filter_bs,
                          0, BLK_PERM_ALL,
                          speed, creation_flags, NULL, NULL, errp);
     if (!s) {
         goto fail;
     }

     s->blk = blk_new_with_bs(cor_filter_bs, BLK_PERM_CONSISTENT_READ,
                              basic_flags | BLK_PERM_WRITE, errp);
     if (!s->blk) {
         goto fail;
     }
     /*
      * Disable request queuing in the BlockBackend to avoid deadlocks on drain:
      * The job reports that it's busy until it reaches a pause point.
      */
     blk_set_disable_request_queuing(s->blk, true);
     blk_set_allow_aio_context_change(s->blk, true);

     /*
      * Prevent concurrent jobs trying to modify the graph structure here, we
      * already have our own plans. Also don't allow resize as the image size is
      * queried only at the job start and then cached.
      */
     bdrv_graph_wrlock();
     if (block_job_add_bdrv(&s->common, "active node", bs, 0,
                            basic_flags | BLK_PERM_WRITE, errp)) {
         bdrv_graph_wrunlock();
         goto fail;
     }

     /* Block all intermediate nodes between bs and base, because they will
      * disappear from the chain after this operation. The streaming job reads
      * every block only once, assuming that it doesn't change, so forbid writes
      * and resizes. Reassign the base node pointer because the backing BS of the
      * bottom node might change after the call to bdrv_reopen_set_read_only()
      * due to parallel block jobs running.
      * above_base node might change after the call to
      * bdrv_reopen_set_read_only() due to parallel block jobs running.
      */
     base = bdrv_filter_or_cow_bs(above_base);
     for (iter = bdrv_filter_or_cow_bs(bs); iter != base;
          iter = bdrv_filter_or_cow_bs(iter))
     {
         ret = block_job_add_bdrv(&s->common, "intermediate node", iter, 0,
                                  basic_flags, errp);
         if (ret < 0) {
             bdrv_graph_wrunlock();
             goto fail;
         }
     }
     bdrv_graph_wrunlock();

     s->base_overlay = base_overlay;
     s->above_base = above_base;
     s->backing_file_str = g_strdup(backing_file_str);
     s->backing_mask_protocol = backing_mask_protocol;
     s->cor_filter_bs = cor_filter_bs;
     s->target_bs = bs;
     s->bs_read_only = bs_read_only;

     s->on_error = on_error;
     trace_stream_start(bs, base, s);
     job_start(&s->common.job);
     return;

 fail:
     if (s) {
         job_early_fail(&s->common.job);
     }
     if (cor_filter_bs) {
         bdrv_cor_filter_drop(cor_filter_bs);
     }
     if (bs_read_only) {
         bdrv_reopen_set_read_only(bs, true, NULL);
     }
     return;

 out_rdlock:
     bdrv_graph_rdunlock_main_loop();
 }
	/*
	* Image streaming
	*
	* Copyright IBM, Corp. 2011
	*
	* Authors:
	* Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
	*
	* This work is licensed under the terms of the GNU LGPL, version 2 or later.
	* See the COPYING.LIB file in the top-level directory.
	*
	*/

	#include "qemu/osdep.h"
	#include "trace.h"
	#include "block/block_int.h"
	#include "block/blockjob_int.h"
	#include "qapi/error.h"
	#include "qapi/qmp/qdict.h"
	#include "qemu/ratelimit.h"
	#include "sysemu/block-backend.h"
	#include "block/copy-on-read.h"

	enum {
	/*
	* Maximum chunk size to feed to copy-on-read. This should be
	* large enough to process multiple clusters in a single call, so
	* that populating contiguous regions of the image is efficient.
	*/
	STREAM_CHUNK = 512 * 1024, /* in bytes */
	};

	typedef struct StreamBlockJob {
	BlockJob common;
	BlockBackend *blk;
	BlockDriverState base_overlay; / COW overlay (stream from this) */
	BlockDriverState above_base; / Node directly above the base */
	BlockDriverState *cor_filter_bs;
	BlockDriverState *target_bs;
	BlockdevOnError on_error;
	char *backing_file_str;
	bool backing_mask_protocol;
	bool bs_read_only;
	} StreamBlockJob;

	static int coroutine_fn stream_populate(BlockBackend *blk,
	int64_t offset, uint64_t bytes)
	{
	assert(bytes < SIZE_MAX);

	return blk_co_preadv(blk, offset, bytes, NULL, BDRV_REQ_PREFETCH);
	}

	static int stream_prepare(Job *job)
	{
	StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
	BlockDriverState *unfiltered_bs;
	BlockDriverState *unfiltered_bs_cow;
	BlockDriverState *base;
	BlockDriverState *unfiltered_base;
	Error *local_err = NULL;
	int ret = 0;

	GLOBAL_STATE_CODE();

	bdrv_graph_rdlock_main_loop();
	unfiltered_bs = bdrv_skip_filters(s->target_bs);
	unfiltered_bs_cow = bdrv_cow_bs(unfiltered_bs);
	bdrv_graph_rdunlock_main_loop();

	/* We should drop filter at this point, as filter hold the backing chain */
	bdrv_cor_filter_drop(s->cor_filter_bs);
	s->cor_filter_bs = NULL;

	/*
	* bdrv_set_backing_hd() requires that the unfiltered_bs and the COW child
	* of unfiltered_bs is drained. Drain already here and use
	* bdrv_set_backing_hd_drained() instead because the polling during
	* drained_begin() might change the graph, and if we do this only later, we
	* may end up working with the wrong base node (or it might even have gone
	* away by the time we want to use it).
	*/
	bdrv_drained_begin(unfiltered_bs);
	if (unfiltered_bs_cow) {
	bdrv_ref(unfiltered_bs_cow);
	bdrv_drained_begin(unfiltered_bs_cow);
	}

	bdrv_graph_rdlock_main_loop();
	base = bdrv_filter_or_cow_bs(s->above_base);
	unfiltered_base = bdrv_skip_filters(base);
	bdrv_graph_rdunlock_main_loop();

	if (unfiltered_bs_cow) {
	const char base_id = NULL, base_fmt = NULL;
	if (unfiltered_base) {
	base_id = s->backing_file_str ?: unfiltered_base->filename;
	if (unfiltered_base->drv) {
	if (s->backing_mask_protocol &&
	unfiltered_base->drv->protocol_name) {
	base_fmt = "raw";
	} else {
	base_fmt = unfiltered_base->drv->format_name;
	}
	}
	}

	bdrv_graph_wrlock();
	bdrv_set_backing_hd_drained(unfiltered_bs, base, &local_err);
	bdrv_graph_wrunlock();

	/*
	* This call will do I/O, so the graph can change again from here on.
	* We have already completed the graph change, so we are not in danger
	* of operating on the wrong node any more if this happens.
	*/
	ret = bdrv_change_backing_file(unfiltered_bs, base_id, base_fmt, false);
	if (local_err) {
	error_report_err(local_err);
	ret = -EPERM;
	goto out;
	}
	}

	out:
	if (unfiltered_bs_cow) {
	bdrv_drained_end(unfiltered_bs_cow);
	bdrv_unref(unfiltered_bs_cow);
	}
	bdrv_drained_end(unfiltered_bs);
	return ret;
	}

	static void stream_clean(Job *job)
	{
	StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);

	if (s->cor_filter_bs) {
	bdrv_cor_filter_drop(s->cor_filter_bs);
	s->cor_filter_bs = NULL;
	}

	blk_unref(s->blk);
	s->blk = NULL;

	/* Reopen the image back in read-only mode if necessary */
	if (s->bs_read_only) {
	/* Give up write permissions before making it read-only */
	bdrv_reopen_set_read_only(s->target_bs, true, NULL);
	}

	g_free(s->backing_file_str);
	}

	static int coroutine_fn stream_run(Job job, Error *errp)
	{
	StreamBlockJob *s = container_of(job, StreamBlockJob, common.job);
	BlockDriverState *unfiltered_bs;
	int64_t len;
	int64_t offset = 0;
	int error = 0;
	int64_t n = 0; /* bytes */

	WITH_GRAPH_RDLOCK_GUARD() {
	unfiltered_bs = bdrv_skip_filters(s->target_bs);
	if (unfiltered_bs == s->base_overlay) {
	/* Nothing to stream */
	return 0;
	}

	len = bdrv_co_getlength(s->target_bs);
	if (len < 0) {
	return len;
	}
	}
	job_progress_set_remaining(&s->common.job, len);

	for ( ; offset < len; offset += n) {
	bool copy;
	int ret;

	/* 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_ratelimit_sleep(&s->common);
	if (job_is_cancelled(&s->common.job)) {
	break;
	}

	copy = false;

	WITH_GRAPH_RDLOCK_GUARD() {
	ret = bdrv_co_is_allocated(unfiltered_bs, offset, STREAM_CHUNK, &n);
	if (ret == 1) {
	/* Allocated in the top, no need to copy. */
	} else if (ret >= 0) {
	/*
	* Copy if allocated in the intermediate images. Limit to the
	* known-unallocated area [offset, offset+n*BDRV_SECTOR_SIZE).
	*/
	ret = bdrv_co_is_allocated_above(bdrv_cow_bs(unfiltered_bs),
	s->base_overlay, true,
	offset, n, &n);
	/* Finish early if end of backing file has been reached */
	if (ret == 0 && n == 0) {
	n = len - offset;
	}

	copy = (ret > 0);
	}
	}
	trace_stream_one_iteration(s, offset, n, ret);
	if (copy) {
	ret = stream_populate(s->blk, offset, n);
	}
	if (ret < 0) {
	BlockErrorAction action =
	block_job_error_action(&s->common, s->on_error, true, -ret);
	if (action == BLOCK_ERROR_ACTION_STOP) {
	n = 0;
	continue;
	}
	if (error == 0) {
	error = ret;
	}
	if (action == BLOCK_ERROR_ACTION_REPORT) {
	break;
	}
	}

	/* Publish progress */
	job_progress_update(&s->common.job, n);
	if (copy) {
	block_job_ratelimit_processed_bytes(&s->common, n);
	}
	}

	/* Do not remove the backing file if an error was there but ignored. */
	return error;
	}

	static const BlockJobDriver stream_job_driver = {
	.job_driver = {
	.instance_size = sizeof(StreamBlockJob),
	.job_type = JOB_TYPE_STREAM,
	.free = block_job_free,
	.run = stream_run,
	.prepare = stream_prepare,
	.clean = stream_clean,
	.user_resume = block_job_user_resume,
	},
	};

	void stream_start(const char job_id, BlockDriverState bs,
	BlockDriverState base, const char backing_file_str,
	bool backing_mask_protocol,
	BlockDriverState *bottom,
	int creation_flags, int64_t speed,
	BlockdevOnError on_error,
	const char *filter_node_name,
	Error **errp)
	{
	StreamBlockJob *s = NULL;
	BlockDriverState *iter;
	bool bs_read_only;
	int basic_flags = BLK_PERM_CONSISTENT_READ \| BLK_PERM_WRITE_UNCHANGED;
	BlockDriverState *base_overlay;
	BlockDriverState *cor_filter_bs = NULL;
	BlockDriverState *above_base;
	QDict *opts;
	int ret;

	GLOBAL_STATE_CODE();

	assert(!(base && bottom));
	assert(!(backing_file_str && bottom));

	bdrv_graph_rdlock_main_loop();

	if (bottom) {
	/*
	* New simple interface. The code is written in terms of old interface
	* with @base parameter (still, it doesn't freeze link to base, so in
	* this mean old code is correct for new interface). So, for now, just
	* emulate base_overlay and above_base. Still, when old interface
	* finally removed, we should refactor code to use only "bottom", but
	* not "base" things.
	*/
	assert(!bottom->drv->is_filter);
	base_overlay = above_base = bottom;
	} else {
	base_overlay = bdrv_find_overlay(bs, base);
	if (!base_overlay) {
	error_setg(errp, "'%s' is not in the backing chain of '%s'",
	base->node_name, bs->node_name);
	goto out_rdlock;
	}

	/*
	* Find the node directly above @base. @base_overlay is a COW overlay,
	* so it must have a bdrv_cow_child(), but it is the immediate overlay
	* of @base, so between the two there can only be filters.
	*/
	above_base = base_overlay;
	if (bdrv_cow_bs(above_base) != base) {
	above_base = bdrv_cow_bs(above_base);
	while (bdrv_filter_bs(above_base) != base) {
	above_base = bdrv_filter_bs(above_base);
	}
	}
	}

	/* Make sure that the image is opened in read-write mode */
	bs_read_only = bdrv_is_read_only(bs);
	if (bs_read_only) {
	/* Hold the chain during reopen */
	if (bdrv_freeze_backing_chain(bs, above_base, errp) < 0) {
	goto out_rdlock;
	}

	ret = bdrv_reopen_set_read_only(bs, false, errp);

	/* failure, or cor-filter will hold the chain */
	bdrv_unfreeze_backing_chain(bs, above_base);

	if (ret < 0) {
	goto out_rdlock;
	}
	}

	bdrv_graph_rdunlock_main_loop();

	opts = qdict_new();

	qdict_put_str(opts, "driver", "copy-on-read");
	qdict_put_str(opts, "file", bdrv_get_node_name(bs));
	/* Pass the base_overlay node name as 'bottom' to COR driver */
	qdict_put_str(opts, "bottom", base_overlay->node_name);
	if (filter_node_name) {
	qdict_put_str(opts, "node-name", filter_node_name);
	}

	cor_filter_bs = bdrv_insert_node(bs, opts, BDRV_O_RDWR, errp);
	if (!cor_filter_bs) {
	goto fail;
	}

	if (!filter_node_name) {
	cor_filter_bs->implicit = true;
	}

	s = block_job_create(job_id, &stream_job_driver, NULL, cor_filter_bs,
	0, BLK_PERM_ALL,
	speed, creation_flags, NULL, NULL, errp);
	if (!s) {
	goto fail;
	}

	s->blk = blk_new_with_bs(cor_filter_bs, BLK_PERM_CONSISTENT_READ,
	basic_flags \| BLK_PERM_WRITE, errp);
	if (!s->blk) {
	goto fail;
	}
	/*
	* Disable request queuing in the BlockBackend to avoid deadlocks on drain:
	* The job reports that it's busy until it reaches a pause point.
	*/
	blk_set_disable_request_queuing(s->blk, true);
	blk_set_allow_aio_context_change(s->blk, true);

	/*
	* Prevent concurrent jobs trying to modify the graph structure here, we
	* already have our own plans. Also don't allow resize as the image size is
	* queried only at the job start and then cached.
	*/
	bdrv_graph_wrlock();
	if (block_job_add_bdrv(&s->common, "active node", bs, 0,
	basic_flags \| BLK_PERM_WRITE, errp)) {
	bdrv_graph_wrunlock();
	goto fail;
	}

	/* Block all intermediate nodes between bs and base, because they will
	* disappear from the chain after this operation. The streaming job reads
	* every block only once, assuming that it doesn't change, so forbid writes
	* and resizes. Reassign the base node pointer because the backing BS of the
	* bottom node might change after the call to bdrv_reopen_set_read_only()
	* due to parallel block jobs running.
	* above_base node might change after the call to
	* bdrv_reopen_set_read_only() due to parallel block jobs running.
	*/
	base = bdrv_filter_or_cow_bs(above_base);
	for (iter = bdrv_filter_or_cow_bs(bs); iter != base;
	iter = bdrv_filter_or_cow_bs(iter))
	{
	ret = block_job_add_bdrv(&s->common, "intermediate node", iter, 0,
	basic_flags, errp);
	if (ret < 0) {
	bdrv_graph_wrunlock();
	goto fail;
	}
	}
	bdrv_graph_wrunlock();

	s->base_overlay = base_overlay;
	s->above_base = above_base;
	s->backing_file_str = g_strdup(backing_file_str);
	s->backing_mask_protocol = backing_mask_protocol;
	s->cor_filter_bs = cor_filter_bs;
	s->target_bs = bs;
	s->bs_read_only = bs_read_only;

	s->on_error = on_error;
	trace_stream_start(bs, base, s);
	job_start(&s->common.job);
	return;

	fail:
	if (s) {
	job_early_fail(&s->common.job);
	}
	if (cor_filter_bs) {
	bdrv_cor_filter_drop(cor_filter_bs);
	}
	if (bs_read_only) {
	bdrv_reopen_set_read_only(bs, true, NULL);
	}
	return;

	out_rdlock:
	bdrv_graph_rdunlock_main_loop();
	}