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https://issues.apache.org/jira/browse/HDFS-16791?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17628570#comment-17628570
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ASF GitHub Bot commented on HDFS-16791:
---------------------------------------
mccormickt12 commented on code in PR #4967:
URL: https://github.com/apache/hadoop/pull/4967#discussion_r1013490718
##########
hadoop-common-project/hadoop-common/src/site/markdown/filesystem/filesystem.md:
##########
@@ -599,6 +599,25 @@ on the filesystem.
if len(FS, P) > 0: getFileStatus(P).getBlockSize() > 0
result == getFileStatus(P).getBlockSize()
+1. The outcome of this operation MUST be identical to the value of
+ `getFileStatus(P).getBlockSize()`.
+2. By inference, it MUST be > 0 for any file of length > 0.
+### `Path getEnclosingRoot(Path p)`
+
+This method is used to find a root directory for a path given. This is useful
for creating
+staging and temp directories in the same root directory. There are constraints
around how
+renames are allowed to atomically occur (ex. across hdfs volumes or across
encryption zones).
+
+#### Preconditions
+
+if no root path is found: raise IOException
+No root path would be found only if there is no mount point for the given path
+
+
+#### Postconditions
+
+The path return will not be null
Review Comment:
added more pre/post, should be more clear now and included some of what you
suggested above
> New API for enclosing root path for a file
> ------------------------------------------
>
> Key: HDFS-16791
> URL: https://issues.apache.org/jira/browse/HDFS-16791
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: Tom McCormick
> Assignee: Tom McCormick
> Priority: Major
> Labels: pull-request-available
>
> At LinkedIn we run many HDFS volumes that are federated by either
> ViewFilesystem or Router Based Federation. As our number of hdfs volumes
> grows, we have a growing need to migrate data seemlessly across volumes.
> Many frameworks have a notion of staging or temp directories, but those
> directories often live in random locations. We want an API getEnclosingRoot,
> which provides the root path a file or dataset.
> In ViewFilesystem / Router Based Federation, the enclosingRoot will be the
> mount point.
> We will also take into account other restrictions for renames like
> encryptions zones.
> If there are several paths (a mount point and an encryption zone), we will
> return the longer path
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