svn commit: r217369 - in head/sys: cam/scsi sys

[Bruce Evans]

On Fri, 14 Jan 2011, Garrett Cooper wrote:

> On Fri, Jan 14, 2011 at 6:42 PM, Bruce Evans <brde at optusnet.com.au> wrote:
>> On Fri, 14 Jan 2011 mdf at FreeBSD.org wrote:
>>
>>> On Thu, Jan 13, 2011 at 10:50 PM, Bruce Evans <brde at optusnet.com.au>
>>> wrote:
>>>>
>>>> On Thu, 13 Jan 2011 mdf at freebsd.org wrote:
>>>>
>>>>> There appear to be 330 uses of SYSCTL and QUAD on the same line in
>>>>> CURRENT.  This seems reasonable to change them to S64, U64 and X64 so
>>>>> they correctly reflect the size they operate upon.
>>>>>
>>>>> What do y'all think?
>>>>
>>>> Now I suggest delaying this until they can be renamed to a type- generic
>>>> SYSCTL_INT() (would probably need to be spelled differently, SYSCTL_I()
>>>> say, even if SYSCTL_INT() was changed at the same time).
>>>
>>> I'm torn on this one.  The compiler knows the type (unless, for
>>> SYSCTL_INT, NULL/0 is used, but that is also a compile-time check),
>>> but to interpret it requires the use of __builtin_foo which is a gcc
>>> extension and not part of standard C.
>>>
>>> Philosophically, while I like this kind of letting the compiler do the
>>> work, if you want C++ you know where to find it.
>>
>> Oops.  I think sizeof() and issigned() can be used to determine the type
>> well enough in functions and initialized data (do a fuller type check if
>> the compiler supports it), but I don't know how to do this in static
>> sysctl declarations (since sizeof() can't be used in cpp expressions).
>
>    Why not just create some dumb testcases that can be run at build
> time to determine that for you?

Well, how?  You are given SYSCTL_I(&var, ...) and have to convert this
to what is now in SYSCTL_INT(), using only the type of var, in hundreds
or thousands of files.  I don't even know how to do this with a test
case for each file, short of parsing all the files.  Oops, I do know
how to translate from sizeof(var) to CTLTYPE_INT or CTLTYPE_UINT.
That's just (sizeof(var) == sizeof(int) ? CTLTYPE_INT : ...).  The
signness is harder (might need gnu typeof(), but not the recent type
checking attributes).  This won't convert from SYSCTL_I() existing
SYSCTL_INT() (the switch on the size would have to be in an ifdef for
that, but sizeof() doesn't work in ifdefs), but it works for generating
CTLTYPE_* internally SYSCTL_I().  The difficulty is converting from a
bare variable `var' to an integer representing the signedness of its
type, without using an unportability like typeof().  With typeof(), this
is:

 	/* Only works for arithmetic types: */
 	#define	isinteger(var)	((typeof(var))0.1 == 0)
 	#define	issigned(var)	((typeof(var))-1 < 0)
 	...

Bruce