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Re: [Qemu-block] [Qemu-devel] [PATCH for-2.10] block/qapi: Remove redund

From: Philippe Mathieu-Daudé
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH for-2.10] block/qapi: Remove redundat NULL check to silence Coverity
Date: Mon, 31 Jul 2017 12:30:04 -0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1

On 07/31/2017 12:17 PM, Jeff Cody wrote:
On Mon, Jul 31, 2017 at 11:54:57AM -0300, Philippe Mathieu-Daudé wrote:
On 07/31/2017 11:38 AM, Jeff Cody wrote:
On Mon, Jul 31, 2017 at 02:51:11PM +0200, Kevin Wolf wrote:
When skipping implicit nodes in bdrv_block_device_info(), we know that
bs0 is always non-NULL; initially, because it's taken from a BdrvChild

Not to mention, we deference bs0 in the chunk of code right above this, so
we'd segfault anyway if the initial value was NULL.

Yes, please move your assert before:

137:    if (bs0->drv && bs0->backing) {

Once there:
Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

I don't think moving the assert() is the correct thing to do, as it is
useful when iterating in the while() via backing_bs().

But maybe adding some asserts would be useful, if we are really concerned.
Looking at the code:

135         }

Maybe add an assert(bs0) here, as you suggest...

137         if (bs0->drv && bs0->backing) {
138             info->backing_file_depth++;
139             bs0 = bs0->backing->bs;

But then maybe we want one here, too?  Or maybe that is overkill :)

140             (*p_image_info)->has_backing_image = true;
141             p_image_info = &((*p_image_info)->backing_image);
142         } else {
143             break;
144         }
146         /* Skip automatically inserted nodes that the user isn't aware of 
147          * query-block (blk != NULL), but not for query-named-block-nodes */
148         while (blk && bs0 && bs0->drv && bs0->implicit) {
149             bs0 = backing_bs(bs0);
150         }

I first thought of inverting the if():

        if (!(bs0->drv && bs0->backing)) {
        bs0 = bs0->backing->bs;
        (*p_image_info)->has_backing_image = true;
        p_image_info = &((*p_image_info)->backing_image);

then read your mail and Kevin's one and realized if 3 ppl disagree commenting the same piece of code that fast, it means this code is not simple enough and surely need refactoring. Now it is not just about silencing Coverity :)

and a BdrvChild never has a NULL bs, and after the first iteration
because implicit nodes always have a backing file.

Remove the NULL check and add an assertion that the implicit node does
indeed have a backing file.

Signed-off-by: Kevin Wolf <address@hidden>

Reviewed-by: Jeff Cody <address@hidden>

  block/qapi.c | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/qapi.c b/block/qapi.c
index d2b18ee9df..5f1a71f5d2 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -145,8 +145,9 @@ BlockDeviceInfo *bdrv_block_device_info(BlockBackend *blk,
          /* Skip automatically inserted nodes that the user isn't aware of for
           * query-block (blk != NULL), but not for query-named-block-nodes */
-        while (blk && bs0 && bs0->drv && bs0->implicit) {
+        while (blk && bs0->drv && bs0->implicit) {
              bs0 = backing_bs(bs0);
+            assert(bs0);

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