Ceph uses extended file attributes to store file meta data. It is a list of key / value pairs. Some file systems implementations do not allow to store more than 2048 characters in the value associated with a key. To overcome this limitation Ceph implements chained extended attributes.
A value that is 5120 character long will be stored in three separate attributes:
- user.key : first 2048 characters
- user.key@1 : next 2048 characters
- user.key@2 : last 1024 characters
The proposed unit tests may be used as a documentation describing in detail how it is implemented from the caller point of view.
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