meta: fix empty value in xattr

[jiefenghuang]

close #5680

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 47.20%. Comparing base (e820195) to head (671228f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5696      +/-   ##
==========================================
- Coverage   54.90%   47.20%   -7.71%     
==========================================
  Files         166      131      -35     
  Lines       48600    39629    -8971     
==========================================
- Hits        26684    18705    -7979     
+ Misses      19002    18711     -291     
+ Partials     2914     2213     -701     

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[davies]

Redis and SQL database support empty values, so we should only fix that for tkv.

The dump/load should be updated also. This is breaking change, since old version of JuiceFS will not know this special value.

[jiefenghuang]

Redis and SQL database support empty values, so we should only fix that for tkv.

The dump/load should be updated also. This is breaking change, since old version of JuiceFS will not know this special value.

I’ll add the compatibility for load/dump.

SQL also needs to be compatible as value is defined with notnull.
This flag can be removed, the main consideration here is whether it’s better for the three engines to maintain the same behavior.

Value []byte `xorm:"blob notnull"`

[davies]

SQL also needs to be compatible as value is defined with notnull. This flag can be removed, the main consideration here is whether it’s better for the three engines to maintain the same behavior.

Value []byte `xorm:"blob notnull"`

Not necessary, this patch is used to workaround a weakness of TiKV.