Re: [patch] ext2_fill_super breakage

[Bill Davidsen]

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 <[e-mail]>
  CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.