git: sys/vfs/hammer: Avoid volume# inconsistency on mount

[Tomohiro Kusumi]

commit c302e84437f9ece78d5cdc8ba4ddaa047d58575b
Author: Tomohiro Kusumi <kusumi.tomohiro at gmail.com>
Date:   Mon Aug 10 04:35:41 2015 +0900

    sys/vfs/hammer: Avoid volume# inconsistency on mount
    
    hammer_vfs_mount() should check and compare # of volumes
    to mount (# of volumes in mount_hammer arg in blkdevs format)
    and vol_count field in volume header.
    
    mount_hammer should fail if they don't match even if it's
    technically possible to mount at the moment after newfs.
    
    In the following Example1, it's possible to safely mount
    /dev/da1 without /dev/da2:/dev/da3 or
    /dev/da1:/dev/da2 without /dev/da3 or
    /dev/da1:/dev/da3 without /dev/da2 at this point because
    both /dev/da2 and /dev/da3 has no data (only layer2 big-block)
    right after newfs_hammer, however if filesystem has enough
    data that zone2 next_offset has already reached the missing
    volume before unmount, there is going to be inconsistency
    between blockmap and actual mounted volumes, which results
    in kernel panic. mount needs to avoid this by checking #
    of volumes as the Example2 shows.
    
    Example 1. - newfs 3 volumes and then mount 2 volumes
      # newfs_hammer -L TEST /dev/da1 /dev/da2 /dev/da3 > /dev/null
      # mount_hammer /dev/da1:/dev/da2:/dev/da3 /HAMMER
      # mount | grep /HAMMER
      TEST on /HAMMER (hammer, local)
      # hammer volume-blkdevs /HAMMER
      /dev/da1:/dev/da2:/dev/da3
      # umount /HAMMER
      # mount_hammer /dev/da1:/dev/da2 /HAMMER
      # mount | grep /HAMMER
      TEST on /HAMMER (hammer, local)
      # hammer volume-blkdevs /HAMMER
      /dev/da1:/dev/da2
    
    Example 2. - with this commit it fails to mount
      # newfs_hammer -L TEST /dev/da1 /dev/da2 /dev/da3 > /dev/null
      # mount_hammer /dev/da1:/dev/da2:/dev/da3 /HAMMER
      # mount | grep /HAMMER
      TEST on /HAMMER (hammer, local)
      # hammer volume-blkdevs /HAMMER
      /dev/da1:/dev/da2:/dev/da3
      # umount /HAMMER
      # mount_hammer /dev/da1:/dev/da2 /HAMMER
      mount_hammer: Unknown error: Invalid argument
      # dmesg | tail -1
      hammer_mount: volume header says 3 volumes, but 2 installed
      # mount_hammer /dev/da1 /HAMMER
      mount_hammer: Unknown error: Invalid argument
      # dmesg | tail -1
      hammer_mount: volume header says 3 volumes, but 1 installed

Summary of changes:
 sys/vfs/hammer/hammer.h        |  1 +
 sys/vfs/hammer/hammer_ondisk.c | 10 ++++++++++
 sys/vfs/hammer/hammer_vfsops.c | 10 ++++++++++
 3 files changed, 21 insertions(+)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/c302e84437f9ece78d5cdc8ba4ddaa047d58575b


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