>
> On Sat, Jan 2, 2010 at 8:10 AM, Shawn <citypw@xxxxxxxxx> wrote:
>>
>> hello guys,
>> I got a newbie confused when I was looking into the source code of
>> s3c2440's RTC driver.I dont know what is __v excatly means.anyone can
>> tell?thanks anyway!
>>
>> #define readb(c) ({ __u8 __v = __raw_readb(__mem_pci(c)); __v; })
On Sun, Jan 3, 2010 at 11:49 AM, Anand Arumugam <anand.arumug@xxxxxxxxx> wrote:
> I think the last __v; inside the macro is to avoid compiler warning or error
> that the unsigned 8-bit variable __v is not being used inside the scope
> defined by the macro.
No, I believe it is the value assigned to the statement sequence
wrapped in the {} pair.
ie. {statement1; statement2; variable} evaluates to the value of the
variable which is the last statement.
Thus c code with:
ret = readb(c);
will assign ret to __v which in turn is the value returned from __raw_readb().
Thus the above macro structure is the standard way to return a value
from a macro. You will find similar macro usage throughout the
kernel.
Greg
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