• Tejun Heo's avatar
    block: implement REQ_FLUSH/FUA based interface for FLUSH/FUA requests · 4fed947c
    Tejun Heo authored
    
    
    Now that the backend conversion is complete, export sequenced
    FLUSH/FUA capability through REQ_FLUSH/FUA flags.  REQ_FLUSH means the
    device cache should be flushed before executing the request.  REQ_FUA
    means that the data in the request should be on non-volatile media on
    completion.
    
    Block layer will choose the correct way of implementing the semantics
    and execute it.  The request may be passed to the device directly if
    the device can handle it; otherwise, it will be sequenced using one or
    more proxy requests.  Devices will never see REQ_FLUSH and/or FUA
    which it doesn't support.
    
    Also, unlike the original REQ_HARDBARRIER, REQ_FLUSH/FUA requests are
    never failed with -EOPNOTSUPP.  If the underlying device doesn't
    support FLUSH/FUA, the block layer simply make those noop.  IOW, it no
    longer distinguishes between writeback cache which doesn't support
    cache flush and writethrough/no cache.  Devices which have WB cache
    w/o flush are very difficult to come by these days and there's nothing
    much we can do anyway, so it doesn't make sense to require everyone to
    implement -EOPNOTSUPP handling.  This will simplify filesystems and
    block drivers as they can drop -EOPNOTSUPP retry logic for barriers.
    
    * QUEUE_ORDERED_* are removed and QUEUE_FSEQ_* are moved into
      blk-flush.c.
    
    * REQ_FLUSH w/o data can also be directly passed to drivers without
      sequencing but some drivers assume that zero length requests don't
      have rq->bio which isn't true for these requests requiring the use
      of proxy requests.
    
    * REQ_COMMON_MASK now includes REQ_FLUSH | REQ_FUA so that they are
      copied from bio to request.
    
    * WRITE_BARRIER is marked deprecated and WRITE_FLUSH, WRITE_FUA and
      WRITE_FLUSH_FUA are added.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Cc: Christoph Hellwig <hch@infradead.org>
    Signed-off-by: default avatarJens Axboe <jaxboe@fusionio.com>
    4fed947c
blk-flush.c 6.49 KB