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.
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
>>>
>>> .
>>>
