On Monday 20 December 2004 14:43, Shourya P. Bhattacharya wrote:
> Hi all,
> Excuse me if this is a very silly question but I was exploring the
> TCP code in the kernel and found the following statement. in
> "include/net/tcp.h"
> #define TCP_CHECK_TIMER(sk) do { } while (0)
> In the function tcp_v4_do_rcv() the above macro is called a few
> times. I could not understand the purpose of that. Aparantly the
> macro is doing nothing.
> I have also checked the FAQ on kernelnewbies related to the "do { ...
> } while (0) " statements, and it says such macros are used to have a
> block of statements without errors on subsitution. But that only
> makes sense if we have some statements inside the do loop.
> Can someone help me out here. I must be missing something very
> obvious.
Hmmm. That is a bit strange. It indeed does nothing.
You often see #define-s like that buy usually they are
conditionally compiled like...
#ifdef FOO
# define foobar() do_something()
#else
# define foobar() do { } while (0)
#endif
My best guess is that it is there for a debugging hook.
Someone could temporally redefine it while working on that code.
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