[Qemu-devel] [PATCH 3/5] block: Support streaming to an intermediate layer

[Alberto Garcia]

This makes sure that the image we are steaming into is open in
read-write mode during the operation.

Operation blockers are also set in all intermediate nodes, since they
will be removed from the chain afterwards.

Finally, this also unblocks the stream operation in backing files.

Signed-off-by: Alberto Garcia <address@hidden>
---
 block.c        |  4 +++-
 block/stream.c | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index 737ab68..6d9cfca 100644
--- a/block.c
+++ b/block.c
@@ -1240,9 +1240,11 @@ void bdrv_set_backing_hd(BlockDriverState *bs, 
BlockDriverState *backing_hd)
             backing_hd->drv ? backing_hd->drv->format_name : "");
 
     bdrv_op_block_all(bs->backing_hd, bs->backing_blocker);
-    /* Otherwise we won't be able to commit due to check in bdrv_commit */
+    /* Otherwise we won't be able to commit or stream */
     bdrv_op_unblock(bs->backing_hd, BLOCK_OP_TYPE_COMMIT_TARGET,
                     bs->backing_blocker);
+    bdrv_op_unblock(bs->backing_hd, BLOCK_OP_TYPE_STREAM,
+                    bs->backing_blocker);
 out:
     bdrv_refresh_limits(bs, NULL);
 }
diff --git a/block/stream.c b/block/stream.c
index 37bfd8b..327d964 100644
--- a/block/stream.c
+++ b/block/stream.c
@@ -33,6 +33,8 @@ typedef struct StreamBlockJob {
     BlockDriverState *base;
     BlockdevOnError on_error;
     char *backing_file_str;
+    int bs_flags;
+    Error *blocker;
 } StreamBlockJob;
 
 static int coroutine_fn stream_populate(BlockDriverState *bs,
@@ -88,8 +90,15 @@ static void stream_complete(BlockJob *job, void *opaque)
 {
     StreamBlockJob *s = container_of(job, StreamBlockJob, common);
     StreamCompleteData *data = opaque;
+    BlockDriverState *i;
     BlockDriverState *base = s->base;
 
+    /* Remove all blockers set in stream_start() */
+    for (i = job->bs->backing_hd; i && i != s->base; i = i->backing_hd) {
+        bdrv_op_unblock_all(i, s->blocker);
+    }
+    error_free(s->blocker);
+
     if (!block_job_is_cancelled(&s->common) && data->reached_end &&
         data->ret == 0) {
         const char *base_id = NULL, *base_fmt = NULL;
@@ -103,6 +112,11 @@ static void stream_complete(BlockJob *job, void *opaque)
         close_unused_images(job->bs, base, base_id);
     }
 
+    /* Reopen the image back in read-only mode if necessary */
+    if (s->bs_flags != bdrv_get_flags(job->bs)) {
+        bdrv_reopen(job->bs, s->bs_flags, NULL);
+    }
+
     g_free(s->backing_file_str);
     block_job_completed(&s->common, data->ret);
     g_free(data);
@@ -246,7 +260,9 @@ void stream_start(BlockDriverState *bs, BlockDriverState 
*base,
                   BlockCompletionFunc *cb,
                   void *opaque, Error **errp)
 {
+    BlockDriverState *i;
     StreamBlockJob *s;
+    int orig_bs_flags;
 
     if ((on_error == BLOCKDEV_ON_ERROR_STOP ||
          on_error == BLOCKDEV_ON_ERROR_ENOSPC) &&
@@ -255,13 +271,33 @@ void stream_start(BlockDriverState *bs, BlockDriverState 
*base,
         return;
     }
 
+    /* Make sure that the image in opened in read-write mode */
+    orig_bs_flags = bdrv_get_flags(bs);
+    if (!(orig_bs_flags & BDRV_O_RDWR)) {
+        Error *local_err = NULL;
+        bdrv_reopen(bs, orig_bs_flags | BDRV_O_RDWR, &local_err);
+        if (local_err != NULL) {
+            error_propagate(errp, local_err);
+            return;
+        }
+    }
+
     s = block_job_create(&stream_job_driver, bs, speed, cb, opaque, errp);
     if (!s) {
         return;
     }
 
+    /* Block all intermediate nodes between bs and base, because they
+     * will disappear from the chain after this operation */
+    error_setg(&s->blocker, "blocked by the block-stream operation in '%s'",
+               bdrv_get_node_name(bs));
+    for (i = bs->backing_hd; i != base && i != NULL; i = i->backing_hd) {
+        bdrv_op_block_all(i, s->blocker);
+    }
+
     s->base = base;
     s->backing_file_str = g_strdup(backing_file_str);
+    s->bs_flags = orig_bs_flags;
 
     s->on_error = on_error;
     s->common.co = qemu_coroutine_create(stream_run);
-- 
2.1.4