Re: Unlinked files

From: Paul H. Hargrove (PHHargrove_at_lbl_dot_gov)
Date: Tue Feb 05 2008 - 14:50:00 PST

  • Next message: Jerome: "Segmentation fault running cr_restart"
    Manish Kumar wrote:
    > hi,
    > why do we save the contents of unlinked file in
    > cr_module/cr_save_open_file() and do corresponding reconstruction by
    > cr_mkunlinked() in its restart counterpart in cr_rstrt_req.c ?
    > I think, its there for process in which a file is open() and unlink()
    > that when process exits, file is automatically closed, if
    > its reference count reaches zero. So if this process is checkpointed,
    > after the unlink() call in its code, there will be no entry in file system
    > corresponding to that file, but the process still needs the in-memory data
    > of file, when reconstructed from the checkpoint file.
    > Please correct me, if I am wrong...or is there any other subtle issue ???
    > -----------------------------------------
    > Manish Kumar
    > Dept. of Computer Science & Engineering
    > Indian Institute of Technology Guwahati
    > Guwahati - 39, INDIA
    > -----------------------------------------
      Your reasoning is correct, except for the phrase "in-memory data".
    Since we cannot know what read or write operations the process may
    conduct after restart, we must restore the entire "in-file" data
    regardless of whether it exists anywhere in memory.  When the unlinked
    file's reference count reached zero, the on-disk copy of the file data
    was removed.  So, BLCR must create its own copy before that happens.
    Paul H. Hargrove                          PHHargrove_at_lbl_dot_gov
    Future Technologies Group
    HPC Research Department                   Tel: +1-510-495-2352
    Lawrence Berkeley National Laboratory     Fax: +1-510-486-6900

  • Next message: Jerome: "Segmentation fault running cr_restart"