haraldwolff/qemu-patch-raspberry4
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block: Remove bdrv_drain_recurse()

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For bdrv_drain(), recursively waiting for child node requests is
pointless because we didn't quiesce their parents, so new requests could
come in anyway. Letting the function work only on a single node makes it
more consistent.

For subtree drains and drain_all, we already have the recursion in
bdrv_do_drained_begin(), so the extra recursion doesn't add anything
either.

Remove the useless code.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Kevin Wolf 2018-03-22 14:35:58 +01:00
parent 89bd030533
commit d30b8e64b7
1 changed files with 3 additions and 33 deletions
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36
block/io.c
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@ -219,38 +219,6 @@ static bool bdrv_drain_poll_top_level(BlockDriverState *bs,
return bdrv_drain_poll(bs, ignore_parent);
}
static bool bdrv_drain_recurse(BlockDriverState *bs, BdrvChild *parent)
{
BdrvChild *child, *tmp;
bool waited;
/* Wait for drained requests to finish */
waited = BDRV_POLL_WHILE(bs, bdrv_drain_poll_top_level(bs, parent));
QLIST_FOREACH_SAFE(child, &bs->children, next, tmp) {
BlockDriverState *bs = child->bs;
bool in_main_loop =
qemu_get_current_aio_context() == qemu_get_aio_context();
assert(bs->refcnt > 0);
if (in_main_loop) {
/* In case the recursive bdrv_drain_recurse processes a
* block_job_defer_to_main_loop BH and modifies the graph,
* let's hold a reference to bs until we are done.
*
* IOThread doesn't have such a BH, and it is not safe to call
* bdrv_unref without BQL, so skip doing it there.
*/
bdrv_ref(bs);
}
waited |= bdrv_drain_recurse(bs, child);
if (in_main_loop) {
bdrv_unref(bs);
}
}
return waited;
}
static void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,
BdrvChild *parent);
static void bdrv_do_drained_end(BlockDriverState *bs, bool recursive,
@ -318,7 +286,9 @@ void bdrv_do_drained_begin(BlockDriverState *bs, bool recursive,
bdrv_parent_drained_begin(bs, parent);
bdrv_drain_invoke(bs, true);
bdrv_drain_recurse(bs, parent);
/* Wait for drained requests to finish */
BDRV_POLL_WHILE(bs, bdrv_drain_poll_top_level(bs, parent));
if (recursive) {
bs->recursive_quiesce_counter++;