• Stefan Behrens's avatar
    Btrfs: handle errors from btrfs_map_bio() everywhere · 61891923
    Stefan Behrens authored
    With the addition of the device replace procedure, it is possible
    for btrfs_map_bio(READ) to report an error. This happens when the
    specific mirror is requested which is located on the target disk,
    and the copy operation has not yet copied this block. Hence the
    block cannot be read and this error state is indicated by
    returning EIO.
    Some background information follows now. A new mirror is added
    while the device replace procedure is running.
    btrfs_get_num_copies() returns one more, and
    btrfs_map_bio(GET_READ_MIRROR) adds one more mirror if a disk
    location is involved that was already handled by the device
    replace copy operation. The assigned mirror num is the highest
    mirror number, e.g. the value 3 in case of RAID1.
    If btrfs_map_bio() is invoked with mirror_num == 0 (i.e., select
    any mirror), the copy on the target drive is never selected
    because that disk shall be able to perform the write requests as
    quickly as possible. The parallel execution of read requests would
    only slow down the disk copy procedure. Second case is that
    btrfs_map_bio() is called with mirror_num > 0. This is done from
    the repair code only. In this case, the highest mirror num is
    assigned to the target disk, since it is used last. And when this
    mirror is not available because the copy procedure has not yet
    handled this area, an error is returned. Everywhere in the code
    the handling of such errors is added now.
    Signed-off-by: default avatarStefan Behrens <sbehrens@giantdisaster.de>
    Signed-off-by: default avatarChris Mason <chris.mason@fusionio.com>
    61891923
volumes.c 131 KB