Re: [Qemu-block] [PATCH 4/6] block: Support streaming to an intermediate layer

[Max Reitz]

On 16.04.2015 16:30, Alberto Garcia wrote:

On Wed 15 Apr 2015 06:09:18 PM CEST, Max Reitz mre...@redhat.com wrote:


+orig_bs_flags = bdrv_get_flags(bs);
+if (!(orig_bs_flags  BDRV_O_RDWR)) {

I feel like we don't want to do this if we're not streaming to an
intermediate layer but to the top layer (because that means there is
some reason for the BDS to be read-only beyond it just being a backing
BDS).

Looks like we don't actually need to do anything, bdrv_reopen_prepare()
already takes care of checking the BDRV_O_ALLOW_RDWR flag, which is not
set if the image was opened in read-only mode.


Oh, that's nice. :-)

Max

[Qemu-block] [PATCH 4/6] 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 be...@igalia.com
---
 block.c|  4 +++-
 block/stream.c | 36 
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index 25289ef..e892cb4 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