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qapi: block-stream: add "bottom" argument

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The code already don't freeze base node and we try to make it prepared
for the situation when base node is changed during the operation. In
other words, block-stream doesn't own base node.

Let's introduce a new interface which should replace the current one,
which will in better relations with the code. Specifying bottom node
instead of base, and requiring it to be non-filter gives us the
following benefits:

 - drop difference between above_base and base_overlay, which will be
   renamed to just bottom, when old interface dropped

 - clean way to work with parallel streams/commits on the same backing
   chain, which otherwise become a problem when we introduce a filter
   for stream job

 - cleaner interface. Nobody will surprised the fact that base node may
   disappear during block-stream, when there is no word about "base" in
   the interface.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20201216061703.70908-11-vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Vladimir Sementsov-Ogievskiy 2020-12-16 09:17:00 +03:00 • committed by Max Reitz
parent 000e5a1cda
commit 7f4a396d76
5 changed files with 94 additions and 31 deletions
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50
block/stream.c
View file

@ -221,6 +221,7 @@ static const BlockJobDriver stream_job_driver = {
void stream_start(const char *job_id, BlockDriverState *bs,
BlockDriverState *base, const char *backing_file_str,
BlockDriverState *bottom,
int creation_flags, int64_t speed,
BlockdevOnError on_error,
const char *filter_node_name,
@ -230,25 +231,42 @@ void stream_start(const char *job_id, BlockDriverState *bs,
BlockDriverState *iter;
bool bs_read_only;
int basic_flags = BLK_PERM_CONSISTENT_READ | BLK_PERM_WRITE_UNCHANGED;
BlockDriverState *base_overlay = bdrv_find_overlay(bs, base);
BlockDriverState *base_overlay;
BlockDriverState *above_base;
if (!base_overlay) {
error_setg(errp, "'%s' is not in the backing chain of '%s'",
base->node_name, bs->node_name);
return;
}
assert(!(base && bottom));
assert(!(backing_file_str && bottom));
/*
* 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);
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);
return;
}
/*
* 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);
}
}
}