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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6373) Remove support for extended attributes on symlinks
Date Tue, 13 May 2014 22:21:15 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6373?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13996975#comment-13996975

Chris Nauroth commented on HDFS-6373:

This makes sense to me, since symlink permissions are always ignored. Linux actually doesn't
even let you change symlink permissions, though it is allowed by the Unix spec. Chris Nauroth,
could you comment on whether this was intentional, or just an oversight? It seems like we
might want to remove ACLs-on-symlinks, which is compatible since symlinks are still hard-disabled.

It is impossible to set an ACL on a symlink.  Any ACL operation run on a symlink automatically
dereferences the symlink and operates on its target, i.e. by passing {{true}} to {{FSDirectory#getINodesInPath4Write}}.
 We wrote tests asserting this behavior, so I don't think there is any way to store an {{AclFeature}}
on an {{INodeSymlink}}.

I quickly skimmed the patch, and it looks like you're going for some additional prevention
inside {{INodeSymlink}} to prevent mistakes.  That seems like a good idea, and we could do
similar for ACLs.

> Remove support for extended attributes on symlinks
> --------------------------------------------------
>                 Key: HDFS-6373
>                 URL: https://issues.apache.org/jira/browse/HDFS-6373
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: namenode
>            Reporter: Andrew Wang
>            Assignee: Charles Lamb
>         Attachments: HDFS-6373.1.patch, HDFS-6373.2.patch
> Looking in the Linux source code, we see the following:
> http://lxr.linux.no/linux+v3.14.3/fs/xattr.c
> {code}
>   60        /*
>   61         * In the user.* namespace, only regular files and directories can have
>   62         * extended attributes. For sticky directories, only the owner and
>   63         * privileged users can write attributes.
>   64         */
> {code}
> We should consider removing {{XAttrFeature}} from {{INodeSymlink}}.

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