Re: [PATCH v12 09/11] qcow2_format.py: collect fields to dump in JSON format - Vladimir Sementsov-Ogievskiy

From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
To: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>,
	qemu-block@nongnu.org
Cc: kwolf@redhat.com, den@openvz.org, qemu-devel@nongnu.org,
	mreitz@redhat.com
Subject: Re: [PATCH v12 09/11] qcow2_format.py: collect fields to dump in JSON format
Date: Wed, 5 Aug 2020 19:58:41 +0300	[thread overview]
Message-ID: <4aff9a66-89e2-2a66-e9d5-46a7e9d650fc@virtuozzo.com> (raw)
In-Reply-To: <1596118512-424960-10-git-send-email-andrey.shinkevich@virtuozzo.com>

30.07.2020 17:15, Andrey Shinkevich wrote:
> As __dict__ is being extended with class members we do not want to
> print, add the to_dict() method to classes that returns a dictionary
> with desired fields and their values. Extend it in subclass when
> necessary to print the final dictionary in the JSON output which
> follows.
> 
> Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
> ---
>   tests/qemu-iotests/qcow2_format.py | 34 ++++++++++++++++++++++++++++++++++
>   1 file changed, 34 insertions(+)
> 
> diff --git a/tests/qemu-iotests/qcow2_format.py b/tests/qemu-iotests/qcow2_format.py
> index 2000de3..a4114cb 100644
> --- a/tests/qemu-iotests/qcow2_format.py
> +++ b/tests/qemu-iotests/qcow2_format.py
> @@ -119,6 +119,9 @@ class Qcow2Struct(metaclass=Qcow2StructMeta):
>   
>               print('{:<25} {}'.format(f[2], value_str))
>   
> +    def to_dict(self):
> +        return dict((f[2], self.__dict__[f[2]]) for f in self.fields)
> +
>   
>   class Qcow2BitmapExt(Qcow2Struct):
>   
> @@ -151,6 +154,11 @@ class Qcow2BitmapExt(Qcow2Struct):
>               print()
>               entry.dump()
>   
> +    def to_dict(self):
> +        fields_dict = super().to_dict()
> +        fields_dict['bitmap_directory'] = self.bitmap_directory
> +        return fields_dict
> +
>   
>   class Qcow2BitmapDirEntry(Qcow2Struct):
>   
> @@ -189,6 +197,14 @@ class Qcow2BitmapDirEntry(Qcow2Struct):
>           super(Qcow2BitmapDirEntry, self).dump()
>           self.bitmap_table.dump()
>   
> +    def to_dict(self):
> +        fields_dict = super().to_dict()
> +        fields_dict['bitmap_table'] = self.bitmap_table.entries

the fact that we have to access internals of bitmap_table is not nice, but let's refactor it later.

> +        bmp_name = dict(name=self.name)
> +        # Put the name ahead of the dict

Aha. I don't think that ordering is necessary for json, but why not to order it a bit.

> +        bme_dict = {**bmp_name, **fields_dict}

strange to create bmp_name dict just to unpack it. You may as well do

bme_dict = {'name': self.name, **fields_dict}

> +        return bme_dict

bme_dict is extra variable: it's created just to return it, so, how about just

return {'name': self.name, **fields_dict}

or, maybe

return {
            'name': self.name,
            **super().to_dict(),
            'bitmap_table': self.bitmap_table.entries
        }

> +
>   
>   class Qcow2BitmapTableEntry(Qcow2Struct):
>   
> @@ -214,6 +230,9 @@ class Qcow2BitmapTableEntry(Qcow2Struct):
>           else:
>               self.type = 'all-zeroes'
>   
> +    def to_dict(self):
> +        return dict(type=self.type, offset=self.offset, reserved=self.reserved)
> +

Python has a special syntax for creating dicts :), let's use:

return {'type': self.type, 'offset': self.offset, 'reserved': self.reserved}

>   
>   class Qcow2BitmapTable:
>   
> @@ -246,6 +265,9 @@ class QcowHeaderExtension(Qcow2Struct):
>               0x44415441: 'Data file'
>           }
>   
> +        def to_dict(self):
> +            return self.mapping.get(self.value, "<unknown>")

aha, so, actually, to_dict() returns not dict, but string. So it should better be named to_json() (and return any json-dumpable object, like string or dict)

and then, we can add to_json() method to Qcow2BitmapTable as well, to return list.

> +
>       fields = (
>           ('u32', Magic, 'magic'),
>           ('u32', '{}', 'length')
> @@ -308,6 +330,18 @@ class QcowHeaderExtension(Qcow2Struct):
>           else:
>               self.obj.dump()
>   
> +    def to_dict(self):
> +        fields_dict = super().to_dict()
> +        ext_name = dict(name=self.Magic(self.magic))

strange that we have to create Magic object here... Ok, let's refactor it later

> +        # Put the name ahead of the dict
> +        he_dict = {**ext_name, **fields_dict}
> +        if self.obj is not None:
> +            he_dict['data'] = self.obj
> +        else:
> +            he_dict['data_str'] = self.data_str
> +
> +        return he_dict

again, let's avoid extra dict variables:

res = {'name': self.Magic(self.magic), **super().to_dict()}
if ...

> +
>       @classmethod
>       def create(cls, magic, data):
>           return QcowHeaderExtension(magic, len(data), data)
> 

-- 
Best regards,
Vladimir