git: HAMMER VFS - Fix probable corruption case when filesystem becomes nearly full

[Matthew Dillon]

commit 07ed04b554263ecb5e36bf8ce5f9cd7e99614e1a
Author: Matthew Dillon <dillon at apollo.backplane.com>
Date:   Sun Apr 18 22:36:14 2010 -0700

    HAMMER VFS - Fix probable corruption case when filesystem becomes nearly full
    
    * The reblocking code was incorrectly assuming the cursor would be pointing
      at a valid node element after an unlock/relock sequence, when it could
      actually be pointing at the EOF of a node.  This case can occur when
      the filesystem is nearly full (possibly due to the reblocking operation
      itself), when the filesystem is also under load from unrelated
      operations.
    
    * This can result in the creation of a corrupted B-Tree leaf node or
      data record.
    
    * Corruption can be checked with hammer checkmap and hammer show
      (as of this rev):
    
      hammer -f device checkmap
    
    	Should output no B-Tree node records or free space mismatches.
    	You will still get the initial volume summary.
    
      hammer -f device show | egrep '^B' | egrep -v '^BM'
    
    	Should output no records.
    
    * Currently the only recourse if corruption is found is to copy off the
      filesystem, newfs_hammer, and copy it back.
    
      Full history and snapshots can be retained by using 'hammer -B mirror-read'
      to copy off the filesystem and mirror-write to copy it back.  However,
      pleaes remember you must do this for each PFS individually.  Make sure
      you have a viable backup before newfsing anything.
    
    Reported-by: Francois Tigeot <ftigeot at wolfpond.org>, Jan Lentfer <Jan.Lentfer at web.de>

Summary of changes:
 sys/vfs/hammer/hammer_reblock.c |   19 ++++++++++++++-----
 1 files changed, 14 insertions(+), 5 deletions(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/07ed04b554263ecb5e36bf8ce5f9cd7e99614e1a


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