• Yan Zheng's avatar
    Btrfs: Seed device support · 2b82032c
    Yan Zheng authored
    
    
    Seed device is a special btrfs with SEEDING super flag
    set and can only be mounted in read-only mode. Seed
    devices allow people to create new btrfs on top of it.
    
    The new FS contains the same contents as the seed device,
    but it can be mounted in read-write mode.
    
    This patch does the following:
    
    1) split code in btrfs_alloc_chunk into two parts. The first part does makes
    the newly allocated chunk usable, but does not do any operation that modifies
    the chunk tree. The second part does the the chunk tree modifications. This
    division is for the bootstrap step of adding storage to the seed device.
    
    2) Update device management code to handle seed device.
    The basic idea is: For an FS grown from seed devices, its
    seed devices are put into a list. Seed devices are
    opened on demand at mounting time. If any seed device is
    missing or has been changed, btrfs kernel module will
    refuse to mount the FS.
    
    3) make btrfs_find_block_group not return NULL when all
    block groups are read-only.
    Signed-off-by: default avatarYan Zheng <zheng.yan@oracle.com>
    2b82032c