[PATCH v2] block: Remove unused BlockDeviceMapEntry

[PATCH v2] block: Remove unused BlockDeviceMapEntry

[Markus Armbruster]

BlockDeviceMapEntry has never been used.  It was added in commit
facd6e2 "so that it is published through the introspection mechanism."
What exactly introspecting types that aren't used for anything could
accomplish isn't clear.  What "introspection mechanism" to use is also
nebulous.  To the best of my knowledge, there has never been one that
covered this type.  Certainly not query-qmp-schema, which includes
only types that are actually used in QMP.

Not being able to introspect BlockDeviceMapEntry hasn't bothered
anyone enough to complain in almost four years.  Get rid of it.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Eric Blake <eblake@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
I found an old patch I neglected to merge.

Max replied to a remark in Eric's review of v1:

    Max Reitz <mreitz@redhat.com> writes:

    > On 2017-07-28 20:10, Eric Blake wrote:
    >> This type is the schema for 'qemu-img map --output=json'.  And I had a
    >> patch once (that I need to revive) that added a JSON Output visitor; at
    >> which point I fixed qemu-img to convert from QAPI to JSON instead of
    >> open-coding its construction of its output string, at which point the
    >> QAPI generated code for this type is useful.
    > (Very late reply, I know, I just stumbled over *MapEntry when looking
    > over block-core.json what we might want to deprecate in 3.0)
    >
    > We already use MapEntry there -- why don't we output just that instead?
    > The only difference seems to be an additional @filename parameter which
    > would probably be actually nice to include in the output.
    >
    > Except that BlockDeviceMapEntry's documentation is better, so we should
    > merge that into MapEntry before removing the former.
    >
    > Max

https://lists.nongnu.org/archive/html/qemu-devel/2017-12/msg02933.html

Me doing the doc update Max suggested could take more than one
iteration, as I know nothing about this stuff.  Max, could you give it
a try?  Feel free to take over my patch.

 qapi/block-core.json | 29 -----------------------------
 1 file changed, 29 deletions(-)

diff --git a/qapi/block-core.json b/qapi/block-core.json
index e00fc27b5e..2aa499a72e 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -418,35 +418,6 @@
 ##
 { 'enum': 'BlockDeviceIoStatus', 'data': [ 'ok', 'failed', 'nospace' ] }
 
-##
-# @BlockDeviceMapEntry:
-#
-# Entry in the metadata map of the device (returned by "qemu-img map")
-#
-# @start: Offset in the image of the first byte described by this entry
-#         (in bytes)
-#
-# @length: Length of the range described by this entry (in bytes)
-#
-# @depth: Number of layers (0 = top image, 1 = top image's backing file, etc.)
-#         before reaching one for which the range is allocated.  The value is
-#         in the range 0 to the depth of the image chain - 1.
-#
-# @zero: the sectors in this range read as zeros
-#
-# @data: reading the image will actually read data from a file (in particular,
-#        if @offset is present this means that the sectors are not simply
-#        preallocated, but contain actual data in raw format)
-#
-# @offset: if present, the image file stores the data for this range in
-#          raw format at the given offset.
-#
-# Since: 1.7
-##
-{ 'struct': 'BlockDeviceMapEntry',
-  'data': { 'start': 'int', 'length': 'int', 'depth': 'int', 'zero': 'bool',
-            'data': 'bool', '*offset': 'int' } }
-
 ##
 # @DirtyBitmapStatus:
 #
-- 
2.26.2

Re: [PATCH v2] block: Remove unused BlockDeviceMapEntry

[Max Reitz]

On 30.10.20 07:24, Markus Armbruster wrote:
> BlockDeviceMapEntry has never been used.  It was added in commit
> facd6e2 "so that it is published through the introspection mechanism."
> What exactly introspecting types that aren't used for anything could
> accomplish isn't clear.  What "introspection mechanism" to use is also
> nebulous.  To the best of my knowledge, there has never been one that
> covered this type.  Certainly not query-qmp-schema, which includes
> only types that are actually used in QMP.
> 
> Not being able to introspect BlockDeviceMapEntry hasn't bothered
> anyone enough to complain in almost four years.  Get rid of it.
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Eric Blake <eblake@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---
> I found an old patch I neglected to merge.
> 
> Max replied to a remark in Eric's review of v1:
> 
>     Max Reitz <mreitz@redhat.com> writes:
> 
>     > On 2017-07-28 20:10, Eric Blake wrote:
>     >> This type is the schema for 'qemu-img map --output=json'.  And I had a
>     >> patch once (that I need to revive) that added a JSON Output visitor; at
>     >> which point I fixed qemu-img to convert from QAPI to JSON instead of
>     >> open-coding its construction of its output string, at which point the
>     >> QAPI generated code for this type is useful.
>     > (Very late reply, I know, I just stumbled over *MapEntry when looking
>     > over block-core.json what we might want to deprecate in 3.0)
>     >
>     > We already use MapEntry there -- why don't we output just that instead?
>     > The only difference seems to be an additional @filename parameter which
>     > would probably be actually nice to include in the output.
>     >
>     > Except that BlockDeviceMapEntry's documentation is better, so we should
>     > merge that into MapEntry before removing the former.
>     >
>     > Max
> 
> https://lists.nongnu.org/archive/html/qemu-devel/2017-12/msg02933.html
> 
> Me doing the doc update Max suggested could take more than one
> iteration, as I know nothing about this stuff.  Max, could you give it
> a try?  Feel free to take over my patch.

Thanks, done :)

https://lists.nongnu.org/archive/html/qemu-block/2020-11/msg00143.html

Max