fix UnknownHostException when visit data with cfs protocol #5
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It throw a UnknownHostException when I using spark to visit data with path like cfs://${volumnName}/xxx.
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The exception is throwed at org.apache.hadoop.security.SecurityUtil.buildTokenService method
I think that token is not required when visit cubefs, We should refer to the implementation of S3AFileSystem. S3AFileSystem. getCanonicalServiceName
It works after I overwrite getCanonicalServiceName method.
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