[Xen-bugs] [Bug 148] New: LVM Snapshots in dom0 attempt to access beyond end of device

[bugzilla-daemon@xxxxxxxxxxxxxxxxxxx]

http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=148

           Summary: LVM Snapshots in dom0 attempt to access beyond end of
                    device
           Product: Xen
           Version: unstable
          Platform: Unspecified
        OS/Version: Linux
            Status: NEW
          Severity: major
          Priority: P2
         Component: Hypervisor
        AssignedTo: xen-bugs@xxxxxxxxxxxxxxxxxxx
        ReportedBy: mjbaysek@xxxxxxxxxx


Here is the scenario:  Trying to use LVM snapshots and tar to backup domU
instances.  I am running the version of Xen that is packaged with Fedora Core 
4.  

On dom0, LVM logical volumes are created for the root filesystem for each domU
instance, and exported as sda1 to the domU instance.  While domU host is
running, a read-only snapshot of the domU logical volume is created in dom0 for
backup purposes.  The snapshot is then mounted in dom0.  When tar is run on the
mounted snapshot, messages such as the following are printed to std err:

tar: bin/bash: File shrank by 679616 bytes; padding with zeros
tar: bin/cp: File shrank by 7612 bytes; padding with zeros
tar: bin/cpio: File shrank by 15968 bytes; padding with zeros
tar: bin/dir: File shrank by 26352 bytes; padding with zeros
tar: bin/ed: File shrank by 19952 bytes; padding with zeros
tar: bin/grep: File shrank by 28264 bytes; padding with zeros
tar: bin/install: File shrank by 9036 bytes; padding with zeros
tar: bin/ls: File shrank by 26352 bytes; padding with zeros
tar: bin/mail: File shrank by 35752 bytes; padding with zeros
tar: bin/mount: File shrank by 21192 bytes; padding with zeros
tar: bin/netstat: File shrank by 51192 bytes; padding with zeros
tar: bin/ps: File shrank by 19692 bytes; padding with zeros
tar: bin/sash: File shrank by 653808 bytes; padding with zeros
tar: bin/sort: File shrank by 408 bytes; padding with zeros
tar: bin/tar: File shrank by 153768 bytes; padding with zeros
tar: bin/vdir: File shrank by 22256 bytes; padding with zeros

Also, messages in syslog:

Aug  8 14:00:08 luke2 kernel: attempt to access beyond end of device
Aug  8 14:00:08 luke2 kernel: dm-12: rw=0, want=25259926792, limit=4194304
Aug  8 14:00:08 luke2 kernel: attempt to access beyond end of device
Aug  8 14:00:08 luke2 kernel: dm-12: rw=0, want=19288968352, limit=4194304
Aug  8 14:00:08 luke2 kernel: attempt to access beyond end of device
Aug  8 14:00:08 luke2 kernel: dm-12: rw=0, want=14719990504, limit=4194304
Aug  8 14:00:08 luke2 kernel: attempt to access beyond end of device
Aug  8 14:00:08 luke2 kernel: dm-12: rw=0, want=9093999384, limit=4194304
Aug  8 14:00:08 luke2 kernel: attempt to access beyond end of device
Aug  8 14:00:08 luke2 kernel: dm-12: rw=0, want=7804042504, limit=4194304
Aug  8 14:00:08 luke2 kernel: attempt to access beyond end of device
Aug  8 14:00:08 luke2 kernel: dm-12: rw=0, want=9276457608, limit=4194304
Aug  8 14:00:08 luke2 kernel: attempt to access beyond end of device
Aug  8 14:00:08 luke2 kernel: dm-12: rw=0, want=21308892424, limit=4194304
Aug  8 14:00:08 luke2 kernel: attempt to access beyond end of device
Aug  8 14:00:08 luke2 kernel: dm-12: rw=0, want=31157396560, limit=4194304
Aug  8 14:00:08 luke2 kernel: attempt to access beyond end of device
Aug  8 14:00:08 luke2 kernel: dm-12: rw=0, want=34359647080, limit=4194304
Aug  8 14:00:08 luke2 kernel: attempt to access beyond end of device
Aug  8 14:00:08 luke2 kernel: dm-12: rw=0, want=19847457232, limit=4194304
Aug  8 14:00:08 luke2 kernel: attempt to access beyond end of device
Aug  8 14:00:08 luke2 kernel: dm-12: rw=0, want=18932580400, limit=4194304
Aug  8 14:00:08 luke2 kernel: attempt to access beyond end of device
Aug  8 14:00:08 luke2 kernel: dm-12: rw=0, want=34359733576, limit=4194304
Aug  8 14:00:08 luke2 kernel: attempt to access beyond end of device
Aug  8 14:00:08 luke2 kernel: dm-12: rw=0, want=748619040, limit=4194304
Aug  8 14:00:08 luke2 kernel: attempt to access beyond end of device
Aug  8 14:00:08 luke2 kernel: dm-12: rw=0, want=31157396560, limit=4194304

Obviously trying to back up this way would result in much data loss.  It's a
shame because it would be such a good way to backup domU's.

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