git: sys/vfs/hammer: Fix mount issue after volume-del

[Tomohiro Kusumi]

commit 78249d7f7c218296742a9f9c46fa094704306a4d
Author: Tomohiro Kusumi <kusumi.tomohiro at gmail.com>
Date:   Mon Aug 3 20:01:48 2015 +0900

    sys/vfs/hammer: Fix mount issue after volume-del
    
    When a volume other than the one with the max volume number
    is removed from filesystem by volume-del, volume numbers are
    no longer sequential. This makes unable to mount the filesystem
    once it's unmounted because code assumes volumes numbers are
    >=0 && <=(N-1) when N is the number of volumes. It needs to
    be able to handle a hole in volume numbers.
    
    For example, the following filesystem initially consists of
    volumes A/B/C where volume A is the root volume(*). Each has
    volume# 0/1/2 in its volume header written by newfs_hammer.
    
    volume  *A-B-C
    volume#  0 1 2
    
    Remove volume B by hammer volume-del. If the filesystem has
    no data yet, it never fails.
    
    volume  *A-C
    volume#  0 2
    
    Unmount filesystem and try to mount again by specifying A:C,
    but mount code assumes filesystem that consists of 2 volumes
    means volume numbers are (A,C)=(0,1)|(1,0)
    but not (A,C)=(0,2)|(2,0)
    
      # newfs_hammer -L TEST /dev/da1 /dev/da2 /dev/da3 > /dev/null
      # mount_hammer /dev/da1:/dev/da2:/dev/da3 /HAMMER
      # hammer volume-blkdevs /HAMMER
      /dev/da1:/dev/da2:/dev/da3
      # hammer volume-del /dev/da2 /HAMMER
      # hammer volume-blkdevs /HAMMER
      /dev/da1:/dev/da3
      # umount /HAMMER
      # mount_hammer /dev/da1:/dev/da3 /HAMMER
      mount_hammer: Unknown error: Invalid argument
      # dmesg | tail -1
      hammer_mount: Missing volumes, cannot mount!
    
    This commit fixes that.
      # newfs_hammer -L TEST /dev/da1 /dev/da2 /dev/da3 > /dev/null
      # mount_hammer /dev/da1:/dev/da2:/dev/da3 /HAMMER
      # hammer volume-blkdevs /HAMMER
      /dev/da1:/dev/da2:/dev/da3
      # hammer volume-del /dev/da2 /HAMMER
      # hammer volume-blkdevs /HAMMER
      /dev/da1:/dev/da3
      # umount /HAMMER
      # mount_hammer /dev/da1:/dev/da3 /HAMMER
      # hammer volume-blkdevs /HAMMER
      /dev/da1:/dev/da3
      # umount /HAMMER
    
    Note that hammer volume-add doesn't assume volume numbers are
    sequential, so it can properly add a volume after removing a
    volume with non-max volume number (see hammer_ioc_volume_add()).

Summary of changes:
 sys/vfs/hammer/hammer.h        | 14 ++++++++++++++
 sys/vfs/hammer/hammer_ondisk.c |  6 +++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/78249d7f7c218296742a9f9c46fa094704306a4d


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