On Tue, Jun 02, 2020 at 10:18:07AM -0500, David Lechner wrote: > On 5/31/20 12:14 PM, William Breathitt Gray wrote: > > Yielding the following /dev/counter0 memory layout: > > > > +------------+-----------------+------------+-------------------+ > > | Byte 0 | Byte 1 - Byte 8 | Byte 9 | Byte 10 - Byte 17 | > > +------------+-----------------+------------+-------------------+ > > | Boundary 0 | Count 0 | Boundary 1 | Count 1 | > > +------------+-----------------+------------+-------------------+ > > A potential pitfall with this sort of packing is that some platforms > do not support unaligned access, so data would have to be "unpacked" > before it could be used. Since the user defines the format of this data, they could reorganize it to a more streamline alignment; for example: # echo "C0 C1 C0E0 C1E0" > counter0/chrdev_format Yielding the following /dev/counter0 memory layout instead: +-----------------+------------------+------------+------------+ | Byte 0 - Byte 7 | Byte 8 - Byte 15 | Byte 16 | Byte 17 | +-----------------+------------------+------------+------------+ | Count 0 | Count 1 | Boundary 0 | Boundary 1 | +-----------------+------------------+------------+------------+ In the future, we could also define a padding argument to give users more control over the exact offsets: # echo "C0E0 P7 C0 C1E0 P7 C1" > counter0/chrdev_format Yielding the following /dev/counter0 memory layout instead: +------------+-----------------+------------------+------------+ | Byte 0 | Byte 1 - Byte 7 | Byte 8 - Byte 15 | Byte 16 | +------------+-----------------+------------------+------------+ | Boundary 0 | Padding | Count 0 | Boundary 1 | +------------+-----------------+------------------+------------+ +-------------------+-------------------+ | Byte 17 - Byte 23 | Byte 24 - Byte 31 | +-------------------+-------------------+ | Padding | Count 1 | +-------------------+-------------------+ I not sure it's best to introduce padding support with this patchset given how much is already changing, but I don't anticipate packing alignment to be something difficult to support in the future with this interface. William Breathitt Gray
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