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From: Max Reitz <mreitz@redhat.com>
To: Kevin Wolf <kwolf@redhat.com>
Cc: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
	qemu-devel@nongnu.org, qemu-block@nongnu.org
Subject: Re: [Qemu-devel] [PATCH v6 14/42] block: Use CAFs when working with backing chains
Date: Mon, 9 Sep 2019 10:25:10 +0200
Message-ID: <c8ef1957-e656-80bf-7e53-a8a417861d26@redhat.com> (raw)
In-Reply-To: <20190905140547.GC4911@localhost.localdomain>

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On 05.09.19 16:05, Kevin Wolf wrote:
> Am 09.08.2019 um 18:13 hat Max Reitz geschrieben:
>> Use child access functions when iterating through backing chains so
>> filters do not break the chain.
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
>>  block.c | 40 ++++++++++++++++++++++++++++------------
>>  1 file changed, 28 insertions(+), 12 deletions(-)
>>
>> diff --git a/block.c b/block.c
>> index 86b84bea21..42abbaf0ba 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -4376,7 +4376,8 @@ int bdrv_change_backing_file(BlockDriverState *bs,
>>  }
>>  
>>  /*
>> - * Finds the image layer in the chain that has 'bs' as its backing file.
>> + * Finds the image layer in the chain that has 'bs' (or a filter on
>> + * top of it) as its backing file.
>>   *
>>   * active is the current topmost image.
>>   *
>> @@ -4388,11 +4389,18 @@ int bdrv_change_backing_file(BlockDriverState *bs,
>>  BlockDriverState *bdrv_find_overlay(BlockDriverState *active,
>>                                      BlockDriverState *bs)
>>  {
>> -    while (active && bs != backing_bs(active)) {
>> -        active = backing_bs(active);
>> +    bs = bdrv_skip_rw_filters(bs);
>> +    active = bdrv_skip_rw_filters(active);
> 
> This does more than the commit message says. In addition to iterating
> through filters instead of stopping, it also changes the semantics of
> the function to return the next non-filter on top of bs instead of the
> next node.

Which is to say the overlay.

(I think we only ever use “overlay” in the COW sense.)

> The block jobs seem to use it only for bdrv_is_allocated_above(), which
> should return the same thing in both cases, so the behaviour stays the
> same. qmp_block_commit() will check op blockers on a different node now,
> which could be a fix or a bug, I can't tell offhand. Probably the
> blocking doesn't really work anyway.

You mean that the op blocker could have been on a block job filter node
before?  I think that‘s pretty much the point of this fix; that that
doesn’t make sense.  (We didn’t have mirror_top_bs and the like at
058223a6e3b.)

> All of this should be mentioned in the commit message at least. Maybe
> it's also worth splitting in two patches.

I don’t know.  The function was written when there were no filters.
This change would have been a no-op then.  The fact that it isn’t to me
just means that introducing filters broke it.

So I don’t know what I would write.  Maybe “bdrv_find_overlay() now
actually finds the overlay, that is, it will not return a filter node.
This is the behavior that all callers expect (because they work on COW
backing chains).”

>> +    while (active) {
>> +        BlockDriverState *next = bdrv_backing_chain_next(active);
>> +        if (bs == next) {
>> +            return active;
>> +        }
>> +        active = next;
>>      }
>>  
>> -    return active;
>> +    return NULL;
>>  }
>>  
>>  /* Given a BDS, searches for the base layer. */
>> @@ -4544,9 +4552,7 @@ int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base,
>>       * other intermediate nodes have been dropped.
>>       * If 'top' is an implicit node (e.g. "commit_top") we should skip
>>       * it because no one inherits from it. We use explicit_top for that. */
>> -    while (explicit_top && explicit_top->implicit) {
>> -        explicit_top = backing_bs(explicit_top);
>> -    }
>> +    explicit_top = bdrv_skip_implicit_filters(explicit_top);
>>      update_inherits_from = bdrv_inherits_from_recursive(base, explicit_top);
>>  
>>      /* success - we can delete the intermediate states, and link top->base */
>> @@ -5014,7 +5020,7 @@ BlockDriverState *bdrv_lookup_bs(const char *device,
>>  bool bdrv_chain_contains(BlockDriverState *top, BlockDriverState *base)
>>  {
>>      while (top && top != base) {
>> -        top = backing_bs(top);
>> +        top = bdrv_filtered_bs(top);
>>      }
>>  
>>      return top != NULL;
>> @@ -5253,7 +5259,17 @@ BlockDriverState *bdrv_find_backing_image(BlockDriverState *bs,
>>  
>>      is_protocol = path_has_protocol(backing_file);
>>  
>> -    for (curr_bs = bs; curr_bs->backing; curr_bs = curr_bs->backing->bs) {
>> +    /*
>> +     * Being largely a legacy function, skip any filters here
>> +     * (because filters do not have normal filenames, so they cannot
>> +     * match anyway; and allowing json:{} filenames is a bit out of
>> +     * scope).
>> +     */
>> +    for (curr_bs = bdrv_skip_rw_filters(bs);
>> +         bdrv_filtered_cow_child(curr_bs) != NULL;
>> +         curr_bs = bdrv_backing_chain_next(curr_bs))
> 
> This could just use bs_below instead of recalculating the node if you
> moved the declaration of bs_below to the function scope.

Indeed, thanks.

Max

>> +    {
>> +        BlockDriverState *bs_below = bdrv_backing_chain_next(curr_bs);
>>  
>>          /* If either of the filename paths is actually a protocol, then
>>           * compare unmodified paths; otherwise make paths relative */


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  reply index

Thread overview: 132+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-09 16:13 [Qemu-devel] [PATCH v6 00/42] block: Deal with filters Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 01/42] block: Mark commit and mirror as filter drivers Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 02/42] copy-on-read: Support compressed writes Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 03/42] throttle: " Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 04/42] block: Add child access functions Max Reitz
2019-08-09 16:56   ` Eric Blake
2019-09-04 16:16   ` Kevin Wolf
2019-09-09  7:56     ` Max Reitz
2019-09-09  9:36       ` Kevin Wolf
2019-09-09 14:04         ` Max Reitz
2019-09-09 16:13           ` Kevin Wolf
2019-09-10  9:14             ` Max Reitz
2019-09-10 10:47               ` Kevin Wolf
2019-09-10 11:36                 ` Max Reitz
2019-09-10 12:48                   ` Kevin Wolf
2019-09-10 12:59                     ` Max Reitz
2019-09-10 13:10                       ` Kevin Wolf
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 05/42] block: Add chain helper functions Max Reitz
2019-08-09 17:01   ` Eric Blake
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 06/42] qcow2: Implement .bdrv_storage_child() Max Reitz
2019-08-09 17:07   ` Eric Blake
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 07/42] block: *filtered_cow_child() for *has_zero_init() Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 08/42] block: bdrv_set_backing_hd() is about bs->backing Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 09/42] block: Include filters when freezing backing chain Max Reitz
2019-08-10 13:32   ` Vladimir Sementsov-Ogievskiy
2019-08-12 12:56     ` Max Reitz
2019-09-05 13:05   ` Kevin Wolf
2019-09-09  8:02     ` Max Reitz
2019-09-09  9:40       ` Kevin Wolf
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 10/42] block: Drop bdrv_is_encrypted() Max Reitz
2019-08-10 13:42   ` Vladimir Sementsov-Ogievskiy
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 11/42] block: Add bdrv_supports_compressed_writes() Max Reitz
2019-09-05 13:11   ` Kevin Wolf
2019-09-09  8:09     ` Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 12/42] block: Use bdrv_filtered_rw* where obvious Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 13/42] block: Use CAFs in block status functions Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 14/42] block: Use CAFs when working with backing chains Max Reitz
2019-08-10 15:19   ` Vladimir Sementsov-Ogievskiy
2019-09-05 14:05   ` Kevin Wolf
2019-09-09  8:25     ` Max Reitz [this message]
2019-09-09  9:55       ` Kevin Wolf
2019-09-09 14:08         ` Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 15/42] block: Re-evaluate backing file handling in reopen Max Reitz
2019-08-10 16:05   ` Vladimir Sementsov-Ogievskiy
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 16/42] block: Flush all children in generic code Max Reitz
2019-08-10 15:36   ` Vladimir Sementsov-Ogievskiy
2019-08-12 12:58     ` Max Reitz
2019-09-05 16:24       ` Kevin Wolf
2019-09-09  8:31         ` Max Reitz
2019-09-09 10:01           ` Kevin Wolf
2019-09-09 14:15             ` Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 17/42] block: Use CAFs in bdrv_refresh_limits() Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 18/42] block: Use CAFs in bdrv_refresh_filename() Max Reitz
2019-08-10 16:22   ` Vladimir Sementsov-Ogievskiy
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 19/42] block: Use CAF in bdrv_co_rw_vmstate() Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 20/42] block/snapshot: Fix fallback Max Reitz
2019-08-10 16:34   ` Vladimir Sementsov-Ogievskiy
2019-08-12 13:06     ` Max Reitz
2019-09-10 11:56   ` Kevin Wolf
2019-09-10 12:04     ` Max Reitz
2019-09-10 12:49       ` Kevin Wolf
2019-09-10 13:06         ` Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 21/42] block: Use CAFs for debug breakpoints Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 22/42] block: Fix bdrv_get_allocated_file_size's fallback Max Reitz
2019-08-10 16:41   ` Vladimir Sementsov-Ogievskiy
2019-08-12 13:09     ` Max Reitz
2019-08-12 17:14       ` Vladimir Sementsov-Ogievskiy
2019-08-12 19:15         ` Max Reitz
2019-09-10 14:52   ` Kevin Wolf
2019-09-11  6:20     ` Max Reitz
2019-09-11  6:55       ` Kevin Wolf
2019-09-11  7:37         ` Max Reitz
2019-09-11  8:27           ` Kevin Wolf
2019-09-11 10:00             ` Max Reitz
2019-09-11 10:31               ` Kevin Wolf
2019-09-11 11:00                 ` Max Reitz
2019-09-12 10:34                   ` Kevin Wolf
2019-11-14 13:11                   ` Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 23/42] blockdev: Use CAF in external_snapshot_prepare() Max Reitz
2019-09-10 15:02   ` Kevin Wolf
2019-09-11  6:21     ` Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 24/42] block: Use child access functions for QAPI queries Max Reitz
2019-08-10 16:57   ` Vladimir Sementsov-Ogievskiy
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 25/42] mirror: Deal with filters Max Reitz
2019-08-12 11:09   ` Vladimir Sementsov-Ogievskiy
2019-08-12 13:26     ` Max Reitz
2019-08-14 15:17       ` Vladimir Sementsov-Ogievskiy
2019-08-31  9:57   ` Vladimir Sementsov-Ogievskiy
2019-09-02 14:35     ` Max Reitz
2019-09-03  8:32       ` Vladimir Sementsov-Ogievskiy
2019-09-09  7:41         ` Max Reitz
2019-09-13 12:55   ` Kevin Wolf
2019-09-16 10:26     ` Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 26/42] backup: " Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 27/42] commit: " Max Reitz
2019-08-31 10:44   ` Vladimir Sementsov-Ogievskiy
2019-09-02 14:55     ` Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 28/42] stream: " Max Reitz
2019-08-12 11:55   ` Vladimir Sementsov-Ogievskiy
2019-09-13 14:16   ` Kevin Wolf
2019-09-16  9:52     ` Max Reitz
2019-09-16 14:47       ` Kevin Wolf
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 29/42] nbd: Use CAF when looking for dirty bitmap Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 30/42] qemu-img: Use child access functions Max Reitz
2019-08-12 12:14   ` Vladimir Sementsov-Ogievskiy
2019-08-12 13:28     ` Max Reitz
2019-08-14 16:04   ` Vladimir Sementsov-Ogievskiy
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 31/42] block: Drop backing_bs() Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 32/42] block: Make bdrv_get_cumulative_perm() public Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 33/42] blockdev: Fix active commit choice Max Reitz
2019-08-09 16:13 ` [Qemu-devel] [PATCH v6 34/42] block: Inline bdrv_co_block_status_from_*() Max Reitz
2019-08-09 16:14 ` [Qemu-devel] [PATCH v6 35/42] block: Fix check_to_replace_node() Max Reitz
2019-08-15 15:21   ` Vladimir Sementsov-Ogievskiy
2019-08-15 17:01     ` Max Reitz
2019-08-16 11:01       ` Vladimir Sementsov-Ogievskiy
2019-08-16 13:30         ` Max Reitz
2019-08-16 14:24           ` Vladimir Sementsov-Ogievskiy
2019-08-09 16:14 ` [Qemu-devel] [PATCH v6 36/42] iotests: Add tests for mirror @replaces loops Max Reitz
2019-08-09 16:14 ` [Qemu-devel] [PATCH v6 37/42] block: Leave BDS.backing_file constant Max Reitz
2019-08-16 16:16   ` Vladimir Sementsov-Ogievskiy
2019-08-09 16:14 ` [Qemu-devel] [PATCH v6 38/42] iotests: Let complete_and_wait() work with commit Max Reitz
2019-08-23  5:59   ` Vladimir Sementsov-Ogievskiy
2019-08-09 16:14 ` [Qemu-devel] [PATCH v6 39/42] iotests: Add filter commit test cases Max Reitz
2019-08-31 11:41   ` Vladimir Sementsov-Ogievskiy
2019-09-02 15:06     ` Max Reitz
2019-08-31 12:35   ` Vladimir Sementsov-Ogievskiy
2019-09-02 15:09     ` Max Reitz
2019-08-09 16:14 ` [Qemu-devel] [PATCH v6 40/42] iotests: Add filter mirror " Max Reitz
2019-08-31 12:35   ` Vladimir Sementsov-Ogievskiy
2019-08-09 16:14 ` [Qemu-devel] [PATCH v6 41/42] iotests: Add test for commit in sub directory Max Reitz
2019-08-09 16:14 ` [Qemu-devel] [PATCH v6 42/42] iotests: Test committing to overridden backing Max Reitz
2019-09-03  9:18   ` Vladimir Sementsov-Ogievskiy

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