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Re: [PATCH v7 02/47] block: Add chain helper functions


From: Andrey Shinkevich
Subject: Re: [PATCH v7 02/47] block: Add chain helper functions
Date: Thu, 9 Jul 2020 12:07:58 +0300
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.9.0

On 09.07.2020 11:24, Max Reitz wrote:
On 08.07.20 19:20, Andrey Shinkevich wrote:
On 25.06.2020 18:21, Max Reitz wrote:
Add some helper functions for skipping filters in a chain of block
nodes.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
   include/block/block_int.h |  3 +++
   block.c                   | 55 +++++++++++++++++++++++++++++++++++++++
   2 files changed, 58 insertions(+)

diff --git a/include/block/block_int.h b/include/block/block_int.h
index bb3457c5e8..5da793bfc3 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -1382,6 +1382,9 @@ BdrvChild *bdrv_cow_child(BlockDriverState *bs);
   BdrvChild *bdrv_filter_child(BlockDriverState *bs);
   BdrvChild *bdrv_filter_or_cow_child(BlockDriverState *bs);
   BdrvChild *bdrv_primary_child(BlockDriverState *bs);
+BlockDriverState *bdrv_skip_implicit_filters(BlockDriverState *bs);
+BlockDriverState *bdrv_skip_filters(BlockDriverState *bs);
+BlockDriverState *bdrv_backing_chain_next(BlockDriverState *bs);
     static inline BlockDriverState *child_bs(BdrvChild *child)
   {
diff --git a/block.c b/block.c
index 5a42ef49fd..0a0b855261 100644
--- a/block.c
+++ b/block.c
@@ -7008,3 +7008,58 @@ BdrvChild *bdrv_primary_child(BlockDriverState
*bs)
         return NULL;
   }
+
+static BlockDriverState *bdrv_do_skip_filters(BlockDriverState *bs,
+                                              bool
stop_on_explicit_filter)
+{
+    BdrvChild *c;
+
+    if (!bs) {
+        return NULL;
+    }
+
+    while (!(stop_on_explicit_filter && !bs->implicit)) {
+        c = bdrv_filter_child(bs);
+        if (!c) {
+            break;
+        }
+        bs = c->bs;
Could it be child_bs(bs) ?
Well, in a sense, but not really.  We need to check whether there is a
child before overwriting @bs (because @bs must stay a non-NULL pointer),
so we wouldn’t have fewer lines of code if we replaced “BdrvChild *c” by
“BlockDriverState *child_bs”, and then used bdrv_child() to set child_bs.

(And because we have to check whether @c is NULL anyway, there is no
real reason to use child_bs(c) instead of c->bs afterwards.)

Got it, thanks.

Andrey

+    }
Reviewed-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Thanks a lot for reviewing!

Pleasure!

Andrey




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