[Bug general/4788] Exe.get() Exceptions are not being thrown

["cagney at redhat dot com" <sourceware-bugzilla@sourceware.org>]

------- Additional Comments From cagney at redhat dot com  2007-07-18 02:39 -------
(In reply to comment #4)
> Replaced Exe.get() with standard File.getCanonicalPath():
> 
> frysk-core/frysk/proc/live/ChangeLog
> 2007-07-16  Mark Wielaard  <mwielaard@redhat.com>
> 
>     * LinuxProc.java (sendrecExe): Use File.getCanonicalPath().
> 
> frysk-imports/frysk/sys/proc/ChangeLog
> 2007-07-16  Mark Wielaard  <mwielaard@redhat.com>
> 
>     * Exe.java: Removed.
>     * cni/Exe.cxx: Likewise.
> 
> Please report if the problem manifests itself even with this patch applied.

This isn't the problem.

frysk.sys.proc.Exe.get() returns the _contents_ of the link /proc/$$/exe, while
File.getCanonicalPath() attempts to resolve a chain of links, using something
like repeated stat and readlink(2) calls to determine a final path.  This leads
to Exe.get() returning strings such as "/bin/bash (deleted)", or occasionally,
what appears to be a corrupt string, while getCanonicalPath will throw an
IOException.

The apparently corrupt string is caused by a kernel "feature" where it is trying
to track the executable as it is renamed.  The "feature" can lead to some
strange sequences.  vis, how things should work:

$ cp /bin/bash /tmp
$ mkdir /tmp/x
$ /tmp/bash
bash$ mv /tmp/bash /tmp/x
bash$ ls -l /proc/$$/exe
 -> /tmp/x/bash

and when something is deleted:

$ cp /bin/bash /tmp
$ /tmp/bash
bash$ rm /tmp/bash
bash$ ls -l /proc/$$/exe
  -> /bin/bash (deleted)

how things get confused:

$ cp /bin/bash /tmp
$ cp /bin/bash /tmp/a-really-long-file
$ /bin/bash
bash$ mv /tmp/a-really-long-file /tmp/bash
bash$ ls -l /proc/$$/exe
  -> /bin/bash

a dump of the contents of the link shows it in fact contains something like:
    /bin/bash^@lly-long-file (deleted)
and this will occur after pre-link as been run.

The existing frysk.sys.proc.Exe was working as designed.

-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=4788

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