Re: [patch] ext2_fill_super breakage

Bill Davidsen
2002-03-28T17:29:32Z

On Thu, 28 Mar 2002, Brian Gerst wrote:

> I'm not sure I follow you here. Compiling this code (gcc 2.96):
>
> int foo1(void) { return sizeof(struct ext2_sb_info); }
> int foo2(struct ext2_sb_info *sbi) { return sizeof(*sbi); }
>
> yields:
>
> 00000b70 <foo1>:
> b70: b8 dc 00 00 00 mov $0xdc,%eax
> b75: c3 ret
>
> 00000b80 <foo2>:
> b80: b8 dc 00 00 00 mov $0xdc,%eax
> b85: c3 ret
>
> The sizes are the same, so unless it makes a difference with another
> version of gcc then this is just a cosmetic change.

Not at all, it's good programming practice. If you use the sizeof(*p)
notation then the code work right, first time, every time, *even if you
change the type of the pointer*. Without that you have to search all the
code following the pointer declaration for a use of the type where the
pointer should have been dereferenced.

Now scale that to the case where you make a similar change in a macro or
typedef. Now you have to search the whole kernel (or NIC drivers, or ...).
Doing it right assures a change in one place will not break things at
random places all of the source tree.

That used to be part of Intro To Programming Computers...

--
bill davidsen <davidsen@tmr.com>
CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.