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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-9972) new APIs for listStatus and globStatus to deal with symlinks
Date Wed, 25 Sep 2013 01:02:03 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-9972?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13777020#comment-13777020
] 

Colin Patrick McCabe commented on HADOOP-9972:
----------------------------------------------

I thought about this for a while, and I think adding a {{listLinkStatus}} function as you
suggest might be a good idea.  It's kind of similar to {{getFileLinkStatus}}.  The nice thing
about this approach is that filesystems which don't yet support symlinks can go back to the
default approach of resolving all links (the same as getFileStatus).

bq. Are you saying network issue can cause unresolved symlink error?

Yes.  Symlinks can be cross-filesystem, and if one filesystem is unreachable, that would be
a network error.

For globStatus, I'd like to do something similar to {{FileContext#create}}, where you have
a varargs argument with {{CreateOpts}}.

One nice thing is that {{FileSystem#globStatus}} is not implemented by subclasses like {{listStatus}}
is.
                
> new APIs for listStatus and globStatus to deal with symlinks
> ------------------------------------------------------------
>
>                 Key: HADOOP-9972
>                 URL: https://issues.apache.org/jira/browse/HADOOP-9972
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: fs
>    Affects Versions: 2.1.1-beta
>            Reporter: Colin Patrick McCabe
>            Assignee: Colin Patrick McCabe
>
> Based on the discussion in HADOOP-9912, we need new APIs for FileSystem to deal with
symlinks.  The issue is that code has been written which is incompatible with the existence
of things which are not files or directories.  For example,
> there is a lot of code out there that looks at FileStatus#isFile, and
> if it returns false, assumes that what it is looking at is a
> directory.  In the case of a symlink, this assumption is incorrect.
> It seems reasonable to make the default behavior of {{FileSystem#listStatus}} and {{FileSystem#globStatus}}
be fully resolving symlinks, and ignoring dangling ones.  This will prevent incompatibility
with existing MR jobs and other HDFS users.  We should also add new versions of listStatus
and globStatus that allow new, symlink-aware code to deal with symlinks as symlinks.

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