• Vivek Goyal's avatar
    block: add partition resize function to blkpg ioctl · c83f6bf9
    Vivek Goyal authored
    Add a new operation code (BLKPG_RESIZE_PARTITION) to the BLKPG ioctl that
    allows altering the size of an existing partition, even if it is currently
    in use.
    
    This patch converts hd_struct->nr_sects into sequence counter because
    One might extend a partition while IO is happening to it and update of
    nr_sects can be non-atomic on 32bit machines with 64bit sector_t. This
    can lead to issues like reading inconsistent size of a partition. Sequence
    counter have been used so that readers don't have to take bdev mutex lock
    as we call sector_in_part() very frequently.
    
    Now all the access to hd_struct->nr_sects should happen using sequence
    counter read/update helper functions part_nr_sects_read/part_nr_sects_write.
    There is one exception though, set_capacity()/get_capacity(). I think
    theoritically race should exist there too but this patch does not
    modify set_capacity()/get_capacity() due to sheer number of call sites
    and I am afraid that change might break something. I have left that as a
    TODO item. We can handle it later if need be. This patch does not introduce
    any new races as such w.r.t set_capacity()/get_capacity().
    
    v2: Add CONFIG_LBDAF test to UP preempt case as suggested by Phillip.
    Signed-off-by: Vivek Goyal's avatarVivek Goyal <vgoyal@redhat.com>
    Signed-off-by: default avatarPhillip Susi <psusi@ubuntu.com>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    c83f6bf9
blkpg.h 1.56 KB