Re: [PATCH 2/2] f2fs: support {d,id,did,x}node checksum

[Chao Yu <yuchao0@huawei.com>]

On 2018/2/28 13:34, Jaegeuk Kim wrote:
> On 02/27, Chao Yu wrote:
>> Ping,
>>
>> On 2018/2/13 15:34, Chao Yu wrote:
>>> Hi Jaegeuk,
>>>
>>> On 2018/2/10 10:52, Chao Yu wrote:
>>>> On 2018/2/10 9:41, Jaegeuk Kim wrote:
>>>>> On 02/01, Chao Yu wrote:
>>>>>>
>>>>>>
>>>>>> On 2018/2/1 6:15, Jaegeuk Kim wrote:
>>>>>>> On 01/31, Chao Yu wrote:
>>>>>>>> On 2018/1/31 10:02, Jaegeuk Kim wrote:
>>>>>>>>> What if we want to add more entries in addition to node_checksum? Do we have
>>>>>>>>> to add a new feature flag at every time? How about adding a layout value instead
>>>>>>>>
>>>>>>>> Hmm.. for previous implementation, IMO, we'd better add a new feature flag at
>>>>>>>> every time, otherwise, w/ extra_nsize only, in current image, we can know a
>>>>>>>> valid range of extended area in node block, but we don't know which
>>>>>>>> fields/features are valid/enabled or not.
>>>>>>>>
>>>>>>>> One more thing is that if we can add one feature flag for each field, we got one
>>>>>>>> more chance to disable it dynamically.
>>>>>>>>
>>>>>>>>> of extra_nsize? For example, layout #1 means node_checksum with extra_nsize=X?
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> What does 1017 mean? We need to make this structure more flexibly for new
>>>>>>>>
>>>>>>>> Yes, using raw 1017 is not appropriate here.
>>>>>>>>
>>>>>>>>> entries. Like this?
>>>>>>>>> 		union {
>>>>>>>>> 			struct node_v1;
>>>>>>>>> 			struct node_v2;
>>>>>>>>> 			struct node_v3;
>>>>>>>>> 			...
>>>>>>>>> 			struct direct_node dn;
>>>>>>>>> 			struct indirect_node in;
>>>>>>>>> 		};
>>>>>>>>> 	};
>>>>>>>>>
>>>>>>>>> 	struct node_v1 {
>>>>>>>>> 		__le32 data[DEF_ADDRS_PER_BLOCK - V1_NSIZE=1];
>>>>>>>>> 		__le32 node_checksum;
>>>>>>>>> 	}
>>>>>>>>>
>>>>>>>>> 	struct node_v2 {
>>>>>>>>> 		__le32 data[DEF_ADDRS_PER_BLOCK - V2_NSIZE=500];
>>>>>>>>
>>>>>>>> Hmm.. If we only need to add one more 4 bytes field in struct node_v2, but
>>>>>>>> V2_NSIZE is defined as fixed 500, there must be 492 bytes wasted.
>>>>>>>>
>>>>>>>> Or we can define V2_NSIZE as 8, but if there comes more and more extended
>>>>>>>> fields, node version count can be a large number, it results in complicated
>>>>>>>> version recognization and handling.
>>>>>>>>
>>>>>>>> One more question is how can we control which fields are valid or not in
>>>>>>>> comp[Vx_NSIZE]?
>>>>>>>>
>>>>>>>>
>>>>>>>> Anyway, what I'm thinking is maybe we can restructure layout of node block like
>>>>>>>> the one used by f2fs_inode:
>>>>>>>>
>>>>>>>> struct f2fs_node {
>>>>>>>> 	union {
>>>>>>>> 		struct f2fs_inode i;
>>>>>>>> 		union {
>>>>>>>> 			struct {
>>>>>>>> 				__le32 node_checksum;
>>>>>>>> 				__le32 feature_field_1;
>>>>>>>> 				__le32 feature_field_2;
>>>>>>>> 				....
>>>>>>>> 				__le32 addr[];
>>>>>>>> 				
>>>>>>>> 			};
>>>>>>>> 			struct direct_node dn;
>>>>>>>> 			struct indirect_node in;
>>>>>>>> 		};
>>>>>>>> 	};
>>>>>>>> 	struct node_footer footer;
>>>>>>>> } __packed;
>>>>>>>>
>>>>>>>> Moving all extended fields to the head of f2fs_node, so we don't have to use
>>>>>>>> macro to indicate actual size of addr.
>>>>>>>
>>>>>>> Thinking what'd be the best way. My concern is, once getting more entries, we
>>>>>>
>>>>>> OK, I think we need more discussion.. ;)
>>>>>>
>>>>>>> can't set each of features individually. Like the second entry should have
>>>>>>
>>>>>> Oh, that will be hard. If we have to avoid that, we have to tag in somewhere
>>>>>> e.g. f2fs_inode::i_flags2 to indicate which new field in f2fs_node is valid, for
>>>>>> example:
>>>>>>
>>>>>> #define F2FS_NODE_CHECKSUM	0x0001
>>>>>> #define F2FS_NODE_FIELD1	0x0002
>>>>>> #define F2FS_NODE_FIELD2	0x0004
>>>>>>
>>>>>> 	union {
>>>>>> 		struct {
>>>>>> 			__le32 node_checksum;
>>>>>> 			__le32 field_1;
>>>>>> 			__le32 field_2;
>>>>>> 			....
>>>>>> 			__le32 addr[];
>>>>>> 		};
>>>>>> 		struct direct_node dn;
>>>>>> 		struct indirect_node in;
>>>>>> 	};
>>>>>>
>>>>>> f2fs_inode::i_flags2 = F2FS_NODE_CHECKSUM | F2FS_NODE_FIELD1
>>>>>> indicates that f2fs_node::node_checksum and f2fs_node::field_1 are valid;
>>>>>>
>>>>>> f2fs_inode::i_flags2 = F2FS_NODE_FIELD1 | F2FS_NODE_FIELD2
>>>>>> indicates that f2fs_node::field_1 and f2fs_node::field_2 are valid.
>>>>>
>>>>> So, that's why I thought we may need a sort of each formats.
>>>>
>>>> Hmm.. if we have two new added fields, there are (2 << 2) combinations
>>>> of all formats, as:
>>>>
>>>> struct original {
>>>> 	__le32 data[DEF_ADDRS_PER_BLOCK];
>>>> }
>>>>
>>>> struct node_v1 {
>>>> 	__le32 data[DEF_ADDRS_PER_BLOCK - V1_NSIZE=1];
>>>> 	__le32 field_1;
>>>> }
>>>>
>>>> struct node_v2 {
>>>> 	__le32 data[DEF_ADDRS_PER_BLOCK - V2_NSIZE=1];
>>>> 	__le32 field_2;
>>>> }
>>>>
>>>> struct node_v2 {
>>>> 	__le32 data[DEF_ADDRS_PER_BLOCK - V3_NSIZE=2];
>>>> 	__le32 field_1;
>>>> 	__le32 field_2;
>>>> }
>>>>
>>>> If we add more new fields, the node version will increase sharply due
>>>> to there is (n << 2) combination with n fields. Right? Any thoughts to
>>>> reduce maintaining overhead on those node versions structures?
>>>
>>> Do you have time to explain more about the design of multiple version structure
>>> for node block, I'm still be confused about two things:
>>> 1. what will we do if we want to add one new field in node structure.
>>> 2. how can we recognize which fields are valid and which ones are invalid.
> 
> Can we discuss this in LSF/MM, if we get an invitation letter? :P

I'm OK, I hope we can get the invitation and reach an agreement about node
extension format, so I can add checksum for node block as soon as possible,
since during development our guys suffer node block inconsistence occasionally,
I hope checksum can relief us from hard debug work on fs. ;)

Thanks,

> 
>>>
>>> Thanks,
>>>
>>>>
>>>> Thanks,
>>>>
>>>>>
>>>>>>
>>>>>> Any thoughts?
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>>> enabled node_checksum, which we may not want to do.
>>>>>>>
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>>
>>>>>>>>> 		__le32 comp[V2_NSIZE];
>>>>>>>>> 	}
>>>>>>>>> 	...
>>>>>>>>>
>>>>>>>>>> +			};
>>>>>>>>>> +			struct direct_node dn;
>>>>>>>>>> +			struct indirect_node in;
>>>>>>>>>> +		};
>>>>>>>>>>  	};
>>>>>>>>>>  	struct node_footer footer;
>>>>>>>>>>  } __packed;
>>>>>>>>>> -- 
>>>>>>>>>> 2.15.0.55.gc2ece9dc4de6
>>>>>>>>>
>>>>>>>>> .
>>>>>>>>>
>>>>
>>>> .
>>>>
>>>
> 
> .
>