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https://issues.apache.org/jira/browse/HDFS-2514?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13139518#comment-13139518
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Eli Collins commented on HDFS-2514:
-----------------------------------
Here's a description of how link resolution works which illustrates the bug,
followed by a fix. The format below is "call by client" -> "value returned by
server". The call to "parent" below occurs in FC#qualifySymlinkTarget.
h2. Absolute links
h3. Link is the 1st path component
Given link -> /file
FC#op(/link) --> ULE
FC#getLinkTarget(/link) --> /file # Because link is final path component
FC#op(/file) # Because "/file" is absolute
h3. Link is the intermediate component
Given link -> /dir2
FC#op(/dir/link/file) --> ULE
FC#getLinkTarget(/dir/link/file) --> /dir2/file # Returns target + remainder
("file")
FC#op(/dir2/file) # Because "/dir2" is absolute
h3. Link is the final component
Given link -> /file
FC#op(/dir/link) --> ULE
FC#getLinkTarget(/dir/link) --> /file # Because link is final path component
FC#op(/file) # Because "/file" is absolute
h2. Relative links
h3. Link is the 1st path component
Given link -> file
FC#op(/link) --> ULE
FC#getLinkTarget(/link) --> file # Because link is final path component
FC#op(parent(/link) + file) # Because "file" is relative
h3. Link is the intermediate component
Give link -> dir2
FC#op(/dir/link/file) --> ULE
FC#getLinkTarget(/dir/link/file) --> dir2/file # Returns target + remainder
("dir2/file")
FC#op(parent(/dir/link/file) + dir2/file) # Because dir2 is relative
(parent + target)
*This is /dir/link/dir2/file, which is incorrect.* This should be
parent(/dir/link) + dir2/file. But the client uses the full path, it doesn't
know where the link in the path is.
h3. Link is the final component
Given link -> file
FC#op(/dir/link) --> ULE
FC#getLinkTarget(/dir/link) --> file # Because link is final path component
FC#op(parent(/dir/link) + file) # Because "file" is relative (parent +
target)
h2. Proposed fix
In the above example, suppose we name the path components as follows..
path: /dir/link/file
target: dir2
preceding: /dir
remainder: /file
We change how the server resolves the path (in
UnresolvedPathException#getResolvedPath). The server is never given a relative
path. If path refers to a link we return the target of the link verbatim (as we
currently do). If target is absolute we return target + remainder (as we
currenty do), otherwise we return preceding + target + remainder. Ie we resolve
the link correctly by replacing the link in the path with it's target. Ie we
no longer return a relative path, we're resolving the relative path in path
(which is absolute) and return that.
We don't need to change the client. If getLinkTarget returns an absolute path
we ignore parent of the link (as we currently do). If getLinkTarget returns a
relative path (because it was called with the link being the final path
component - which we know now because the link target is not absolute) then we
append the link's parent and the target, which is now correct since we know the
link is the final path component.
Here's how the failing example works now..
Give link -> dir2
FC#op(/dir/link/file) --> ULE
FC#getLinkTarget(/dir/link/file) --> /dir/dir2/file # Returns preceding +
target + remainder
FC#op(/dir/dir2/file) # Because /dir/dir2/file
is absolute
> Link resolution bug for intermediate symlinks with relative targets
> -------------------------------------------------------------------
>
> Key: HDFS-2514
> URL: https://issues.apache.org/jira/browse/HDFS-2514
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: name-node
> Affects Versions: 0.21.0, 0.22.0, 0.23.0
> Reporter: Eli Collins
> Assignee: Eli Collins
> Attachments: hdfs-2514-1.patch
>
>
> There's a bug in the way the Namenode resolves intermediate symlinks (ie the
> symlink is not the final path component) in paths when the symlink's target
> is a relative path. Will post the full description in the first comment.
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