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From "Andrew Wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4771) Remove the assumption that symlink is inside HDFS namespace and resolvable
Date Wed, 01 May 2013 16:08:15 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4771?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13646672#comment-13646672
] 

Andrew Wang commented on HDFS-4771:
-----------------------------------

Hey [~daryn], thanks for the info. I did some searching, and I'm not sure how common this
behavior is. The Open Group man page for chmod has this to say [1]:

{noformat}
Some implementations might allow changing the mode of symbolic links. This is not supported
by the interfaces in the POSIX specification.
{noformat}

The Linux man page for chmod says this [2]:

{noformat}
chmod never changes the permissions of symbolic links; the chmod system call cannot change
their permissions. This is not a problem since the permissions of symbolic links are never
used.
{noformat}

Not to say that permissions aren't potentially useful though. I think Brandon intended something
different for this JIRA though, since HDFS-948 captures setting permissions and owners on
symlinks.

[1]: http://pubs.opengroup.org/onlinepubs/9699919799/functions/fchmodat.html
[2]: http://linux.die.net/man/1/chmod
                
> Remove the assumption that symlink is inside HDFS namespace and resolvable
> --------------------------------------------------------------------------
>
>                 Key: HDFS-4771
>                 URL: https://issues.apache.org/jira/browse/HDFS-4771
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 3.0.0
>            Reporter: Brandon Li
>
> Currently HDFS always resolves symlink when setting certain file attributes, such as
setPermission and setTime. And thus the client can't set some file attributes of the symlink
itself.
> Two major problems with current symlink support:
>  1. HDFS assumes the link is inside its own namespace. This is a problem when HDFS is
integrated into client's file system namespace.
> 2. Suppose the linked target is inside HFDS, HDFS doesn't really check whether the target
saved in the link file is a valid path. Even the target was valid, it could become invalid
as the namespace changes.
> For example, create a symlink /user/brandon/iamlink.lnk and it has the content(target)
as "/invalid/path". The file /user/brandon/iamlink.lnk can't be deleted since HDFS can't resolve
it.

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