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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4044) Create symbolic links in HDFS
Date Mon, 27 Oct 2008 17:38:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4044?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12642970#action_12642970
] 

Doug Cutting commented on HADOOP-4044:
--------------------------------------

The src/core parts of this patch look good to me. 

One nit: since maxPathLinks is not settable, it should be a private constant MAX_PATH_LINKS
for now.  And 1000 seems way too big.  Linux limited links to 5 for a long time, but Posix
specifies a minimum of 8.  So we should probably choose somewhere between 8 and 32.

If folks find this to be a problem, we could make the limit configurable, or we could simply
detect loops:

{code}
  T resolve(FileSystem fs, Path p) throws IOException {
    T in = next(fs, p);
    Path first = p;
    HashSet seen = new HashSet();
          
    // continue looping till there are no more symbolic links in the path.
    while (in.isLink()) {
      seen.add(p);

      // construct new path
      p = in.getLink();

      if (seen.contains(p))
        throw new IOException("Loop in symbolic links " + first);
      }
      ...
}
{code}

> Create symbolic links in HDFS
> -----------------------------
>
>                 Key: HADOOP-4044
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4044
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: dfs
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>         Attachments: HADOOP-4044-strawman.patch, symLink1.patch, symLink1.patch, symLink11.patch,
symLink4.patch, symLink5.patch, symLink6.patch, symLink8.patch, symLink9.patch
>
>
> HDFS should support symbolic links. A symbolic link is a special type of file that contains
a reference to another file or directory in the form of an absolute or relative path and that
affects pathname resolution. Programs which read or write to files named by a symbolic link
will behave as if operating directly on the target file. However, archiving utilities can
handle symbolic links specially and manipulate them directly.

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