Re: [Qemu-block] [PATCH v6 14/42] block: Use CAFs when working with backing chains
On 09.09.19 11:55, Kevin Wolf wrote:
> Am 09.09.2019 um 10:25 hat Max Reitz geschrieben:
>> 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
---
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.)
>
> I think we do, but so far also only ever for immediate COW childs, not
> for skipping through intermediate node.
Yes, because it’s broken so far.
>>> 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.)
>
> On the off chance that the op blocker actually works, it can't be a job
> filter. I was thinking more of throttling, blkdebug etc.
Well, that’s just broken altogether right now.
>>> 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.
>
> I doubt it. blkdebug is a really old filter.
>
>> 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).”
>
> Maybe just something like "In addition, filter nodes are not returned as
> overlays any more. Instead, the first non-filter node on top of bs is
> considered the overlay now."?
Isn’t that basically the same? :-)
Max
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Re: [Qemu-block] [PATCH v6 14/42] block: Use CAFs when working with backing chains
Am 09.09.2019 um 10:25 hat Max Reitz geschrieben:
> 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
> >> ---
> >> 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.)
I think we do, but so far also only ever for immediate COW childs, not
for skipping through intermediate node.
> > 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.)
On the off chance that the op blocker actually works, it can't be a job
filter. I was thinking more of throttling, blkdebug etc.
> > 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.
I doubt it. blkdebug is a really old filter.
> 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).”
Maybe just something like "In addition, filter nodes are not returned as
overlays any more. Instead, the first non-filter node on top of bs is
considered the overlay now."?
Kevin
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Re: [Qemu-block] [PATCH v6 14/42] block: Use CAFs when working with backing chains
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
>> ---
>> 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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Re: [Qemu-block] [PATCH v6 14/42] block: Use CAFs when working with backing chains
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
> ---
> 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.
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.
All of this should be mentioned in the commit message at least. Maybe
it's also worth splitting in two patches.
> +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.
> +{
> +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 */
> @@ -5261,7 +5277,7 @@ BlockDriverState
> *bdrv_find_backing_image(BlockDriverState *bs,
> char *backing_file_full_ret;
>
> if (strcmp(backing_file, curr_bs->backing_file) == 0) {
> -retval = curr_bs->backing->bs;
> +retval = bs_below;
> break;
> }
> /* Also check against the full backing filename for the image */
> @@ -5271,7 +5287,7 @@ BlockDriverState
> *bdrv_find_backing_image(BlockDriverState *bs,
> bool equal = strcmp(backing_file, backing_file_full_ret) ==
> 0;
> g_free(backing_file_full_ret);
> if (equal) {
> -retval = curr_bs->backing->bs;
> +retval = bs_below;
> break;
> }
> }
> @@ -5297,7 +5313,7 @@ BlockDriverState
> *bdrv_find_backing_image(BlockDriverState *bs,
> g_fr
Re: [Qemu-block] [PATCH v6 14/42] block: Use CAFs when working with backing chains
09.08.2019 19:13, Max Reitz wrote: > Use child access functions when iterating through backing chains so > filters do not break the chain. > > Signed-off-by: Max Reitz Reviewed-by: Vladimir Sementsov-Ogievskiy -- Best regards, Vladimir
[Qemu-block] [PATCH v6 14/42] block: Use CAFs when working with backing chains
Use child access functions when iterating through backing chains so
filters do not break the chain.
Signed-off-by: Max Reitz
---
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);
+
+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))
+{
+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 */
@@ -5261,7 +5277,7 @@ BlockDriverState
*bdrv_find_backing_image(BlockDriverState *bs,
char *backing_file_full_ret;
if (strcmp(backing_file, curr_bs->backing_file) == 0) {
-retval = curr_bs->backing->bs;
+retval = bs_below;
break;
}
/* Also check against the full backing filename for the image */
@@ -5271,7 +5287,7 @@ BlockDriverState
*bdrv_find_backing_image(BlockDriverState *bs,
bool equal = strcmp(backing_file, backing_file_full_ret) == 0;
g_free(backing_file_full_ret);
if (equal) {
-retval = curr_bs->backing->bs;
+retval = bs_below;
break;
}
}
@@ -5297,7 +5313,7 @@ BlockDriverState
*bdrv_find_backing_image(BlockDriverState *bs,
g_free(filename_tmp);
if (strcmp(backing_file_full, filename_full) == 0) {
-retval = curr_bs->backing->bs;
+retval = bs_below;
break;
}
}
--
2.21.0
