Sailesh Mukil created HDFS-11529:
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             Summary: libHDFS still does not return appropriate error 
information in many cases
                 Key: HDFS-11529
                 URL: https://issues.apache.org/jira/browse/HDFS-11529
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: libhdfs
    Affects Versions: 2.6.0
            Reporter: Sailesh Mukil
            Priority: Critical


libHDFS uses a table to compare exceptions against and returns a corresponding 
error code to the application in case of an error.

However, this table is manually populated and many times is disremembered when 
new exceptions are added.

This causes libHDFS to return EINTERNAL (or Unknown Error(255)) whenever these 
exceptions are hit. These are some examples of exceptions that have been 
observed on an Error(255):

org.apache.hadoop.ipc.StandbyException (Operation category WRITE is not 
supported in state standby)

java.io.EOFException: Cannot seek after EOF

javax.security.sasl.SaslException: GSS initiate failed [Caused by GSSException: 
No valid credentials provided (Mechanism level: Failed to find any Kerberos tgt)

It is of course not possible to have an error code for each and every type of 
exception, so one suggestion of how this can be addressed is by having a call 
such as hdfsGetLastException() that would return the last exception that a 
libHDFS thread encountered. We can make use of the Thread Local Storage to 
store this information. Also, this makes sure that the current functionality is 
preserved.

This is a follow up from HDFS-4997.




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