Re: typedefs and structs [was Re: [PATCH 16/42]: PCI: PCI Error reporting callbacks]

[Greg KH <greg@kroah.com>]

On Mon, Nov 07, 2005 at 02:41:36PM -0600, linas wrote:
> On Mon, Nov 07, 2005 at 12:02:57PM -0800, Greg KH was heard to remark:
> > On Mon, Nov 07, 2005 at 01:36:00PM -0600, linas wrote:
> > > On Mon, Nov 07, 2005 at 11:02:45AM -0800, Greg KH was heard to remark:
> > > > 
> > > > No, never typedef a struct.  That's just wrong.  
> > > 
> > > Its a defacto convention for most C-language apps, see, for 
> > > example Xlib, gtk and gnome.
> > 
> > The kernel is not those projects.
> 
> !!

Yeah, anyone who thinks that Xlib is the paradigm for coding style...

> > > Also, "grep typedef include/linux/*" shows that many kernel device
> > > drivers use this convention.
> > 
> > They are wrong and should be fixed.
> 
> What, precisely, is wrong?
> 
> > See my old OLS paper on all about the problems of using typedefs in
> > kernel code.
> 
> Is this on the web somewhere? Google is having trouble finding it.

http://www.kroah.com/linux/talks/ols_2002_kernel_codingstyle_paper/codingstyle.ps
and the presentation is at:
http://www.kroah.com/linux/talks/ols_2002_kernel_codingstyle_talk/html/

> > > > gcc should warn you
> > > > just the same if you pass the wrong struct pointer 
> > > 
> > > There were many cases where it did not warn (I don't remember 
> > > the case of subr calls). I beleive this had to do with ANSI-C spec
> > > issues dating to the 1990's; traditional C is weakly typed.
> > > 
> > > Its not just gcc; anyoe who coded for a while eventually discovered
> > > that tyedefs where strongly typed, but "struct blah *" were not.
> > 
> > Sorry, but you are using a broken compiler if it doesn't complain about
> > this.
> 
> Uhh, gcc? 

Try it in the kernel today.  You will get a warning if you pass in a
pointer to a different structure type than it was defined as.

> I was simply stating a fact about gcc and about standard ANSI-C 
> type-checking that is "well known" to anyone who's been around the 
> block. I was not trying to start an argument.

Then let's end it here...

thanks,

greg k-h