[Bug 103111] New: auto_da_alloc mount option not working

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https://bugzilla.kernel.org/show_bug.cgi?id=103111

            Bug ID: 103111
           Summary: auto_da_alloc mount option not working
           Product: File System
           Version: 2.5
    Kernel Version: 2.6.39
          Hardware: Intel
                OS: Linux
              Tree: Fedora
            Status: NEW
          Severity: normal
          Priority: P1
         Component: ext4
          Assignee: fs_ext4@kernel-bugs.osdl.org
          Reporter: patelrakeshcomp@gmail.com
        Regression: No

As per the ext4 guide,
ext4 will detect the replace-via-rename and replace-via-truncate patterns
              and force that any delayed allocation blocks are allocated such
that at the next journal commit, in  the
              default data=ordered mode, the data blocks of the new file are
forced to disk before the rename() opera‐
              tion is committed.


But it looks like this feature is not working anymore.

Kernel version: 2.6.39.
Filesystem: ext4

Here is the sample code:

  ofstream myfile;

  myfile.open ("example.txt",std::ofstream::trunc);

  myfile << "Writing this to a file.\n";

  system("mv example.txt example.txt1");

Expected behaviour: Ext4 should detect trunc() call and should allocate blocks
for same. So there should be no zero-length file after abnormal
shutdown(withing 30sec).

Actual results: File is having zero-length after abnormal reboot(power outage).

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