[stgt] [PATCH] Add an array that describes which opcodes are supported by the RDWR and SHEEPDOG backends.

[FUJITA Tomonori]

On Thu, 07 Nov 2013 13:46:36 -0800
Dan Mick <dan.mick at inktank.com> wrote:

> 
>>>> I see, thanks. Using the bitmaps is simpler than the array of char if
>>>> you calculate delta and such?
>>>
>>> I think using the array with opcode names is simpler for a human to
>>> comparing when reading the sourcecode.
>>>
>>>
>>> I had a bitmap of 32 bytes, one bit for each opcode,   and I also
>>> tried using an array of 256 bytes, one byte 0/1 for each opcode
>>> but it was horrible to read from a human standpoint.
>>>
>>> When reading the code and the bitmap/array it was very difficult to
>>> see which opcodes were supported and which were not
>>> by just looking at the bits.
>>> It was also errorprone and I did several mistakes when building the
>>> bitmap manually.
>>
>> Why you built it manually? You can do something like
>>
>> set_bit(WRITE_6, bitmap_addr);
>>
>> ?
>>
>> As usual, you can steal bitmap functions from Linux kernel.
> 
> Is it worth it to mess around with bits when chars are easily
> manipulated?  Sure, it's 8x the data, but it's much easier to dump,
> examine in debuggers, etc., and it's 256 bytes; hardly worthy of
> notice.
> Bitmaps are a pain in general.

Most of us (kernel people) are familar with bitmap ops rather than
functions that we would invent. That's my point.
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