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https://issues.apache.org/jira/browse/HDFS-6326?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13995493#comment-13995493
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Chris Nauroth commented on HDFS-6326:
-------------------------------------
Here is a recap of some offline discussion between me and Haohui. Summary: we
are reaching consensus around inclusion of an ACL bit, with the approach of
hiding the bit from other callers as done in my v3 patch. There will be some
additional changes, which I'll fold into a new version of the patch to upload
later. This also will incorporate Daryn's feedback.
bq. I have no problem to declare this is a wrong assumption but the sad fact is
that 3rd-party clients might depend on it.
We agreed on taking a conservative approach of using an ACL bit, but making it
invisible to current callers of {{FsPermission#toShort}}. The technique is
already demonstrated in my v3 patch.
bq. Provided that the FileStatus field is relatively short (~200 bytes), adding
a field for ACL increases the network traffic for listing files by 5%.
This is not a problem for the HDFS {{ClientProtocol}} RPC. That protocol
already encodes {{FsPermission}} as a protobuf uint32, and my patch isn't going
to change that. It's just going to toggle on a bit of the uint32 that was
unused previously.
This is a problem for WebHDFS, which will start returning an additional
{{"aclBit": true}} in JSON responses. To mitigate this, the {{aclBit}} field
will be excluded from the JSON response when there is no ACL. IOW, you'll
never see {{"aclBit": false}}. This means that if ACLs are not in use, then
there is no additional cost. Patch v3 already implements it this way.
> WebHdfs ACL compatibility is broken
> -----------------------------------
>
> Key: HDFS-6326
> URL: https://issues.apache.org/jira/browse/HDFS-6326
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: webhdfs
> Affects Versions: 3.0.0, 2.4.0
> Reporter: Daryn Sharp
> Assignee: Chris Nauroth
> Priority: Blocker
> Attachments: HDFS-6326.1.patch, HDFS-6326.2.patch, HDFS-6326.3.patch
>
>
> 2.4 ACL support is completely incompatible with <2.4 webhdfs servers. The NN
> throws an {{IllegalArgumentException}} exception.
> {code}
> hadoop fs -ls webhdfs://nn/
> Found 21 items
> ls: Invalid value for webhdfs parameter "op": No enum constant
> org.apache.hadoop.hdfs.web.resources.GetOpParam.Op.GETACLSTATUS
> [... 20 more times...]
> {code}
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