• Tejun Heo's avatar
    block: drop request->hard_* and *nr_sectors · 2e46e8b2
    Tejun Heo authored
    struct request has had a few different ways to represent some
    properties of a request.  ->hard_* represent block layer's view of the
    request progress (completion cursor) and the ones without the prefix
    are supposed to represent the issue cursor and allowed to be updated
    as necessary by the low level drivers.  The thing is that as block
    layer supports partial completion, the two cursors really aren't
    necessary and only cause confusion.  In addition, manual management of
    request detail from low level drivers is cumbersome and error-prone at
    the very least.
    Another interesting duplicate fields are rq->[hard_]nr_sectors and
    rq->{hard_cur|current}_nr_sectors against rq->data_len and
    rq->bio->bi_size.  This is more convoluted than the hard_ case.
    rq->[hard_]nr_sectors are initialized for requests with bio but
    blk_rq_bytes() uses it only for !pc requests.  rq->data_len is
    initialized for all request but blk_rq_bytes() uses it only for pc
    requests.  This causes good amount of confusion throughout block layer
    and its drivers and determining the request length has been a bit of
    black magic which may or may not work depending on circumstances and
    what the specific LLD is actually doing.
    rq->{hard_cur|current}_nr_sectors represent the number of sectors in
    the contiguous data area at the front.  This is mainly used by drivers
    which transfers data by walking request segment-by-segment.  This
    value always equals rq->bio->bi_size >> 9.  However, data length for
    pc requests may not be multiple of 512 bytes and using this field
    becomes a bit confusing.
    In general, having multiple fields to represent the same property
    leads only to confusion and subtle bugs.  With recent block low level
    driver cleanups, no driver is accessing or manipulating these
    duplicate fields directly.  Drop all the duplicates.  Now rq->sector
    means the current sector, rq->data_len the current total length and
    rq->bio->bi_size the current segment length.  Everything else is
    defined in terms of these three and available only through accessors.
    * blk_recalc_rq_sectors() is collapsed into blk_update_request() and
      now handles pc and fs requests equally other than rq->sector update.
      This means that now pc requests can use partial completion too (no
      in-kernel user yet tho).
    * bio_cur_sectors() is replaced with bio_cur_bytes() as block layer
      now uses byte count as the primary data length.
    * blk_rq_pos() is now guranteed to be always correct.  In-block users
    * blk_rq_bytes() is now guaranteed to be always valid as is
      blk_rq_sectors().  In-block users converted.
    * blk_rq_sectors() is now guaranteed to equal blk_rq_bytes() >> 9.
      More convenient one is used.
    * blk_rq_bytes() and blk_rq_cur_bytes() are now inlined and take const
      pointer to request.
    [ Impact: API cleanup, single way to represent one property of a request ]
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Cc: Boaz Harrosh <bharrosh@panasas.com>
    Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
blk-merge.c 9.43 KB