Re: [PATCH] mkfs: check sizes of important structs at build time

[Hitoshi Mitake <mitake.hitoshi-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

At Sat, 4 Jan 2014 18:39:58 +0300,
Vyacheslav Dubeyko wrote:
> 
> 
> On Jan 4, 2014, at 4:54 PM, Hitoshi Mitake wrote:
> 
> > On Sat, Jan 4, 2014 at 11:52 PM, Vyacheslav Dubeyko <slava-yeENwD64cLxBDgjK7y7TUQ@public.gmane.org> wrote:
> >> 
> >> On Jan 4, 2014, at 4:29 PM, Hitoshi Mitake wrote:
> >> 
> >>> Current nilfs_check_ondisk_sizes() checks sizes of important structs
> >>> at run time. The checking should be done at build time. This patch
> >>> adds a new macro, BUILD_BUG_ON(), for this purpose. It is similar to
> >>> static_assert() of C++11. If an argument is true, the macro causes a
> >>> bulid error.
> >>> 
> >>> Below is an example of BUILD_BUG_ON(). When the checked conditions are
> >>> true like below:
> >>> 
> >>> /* intentional change for testing BUILD_BUG_ON() */
> >>> 
> >>> static __attribute__((used)) void nilfs_check_ondisk_sizes(void)
> >>> {
> >>>      BUILD_BUG_ON(sizeof(struct nilfs_inode) > NILFS_MIN_BLOCKSIZE);
> >> 
> >> So, why do we need to have function for the case of checking on compilation
> >> phase?
> > 
> > Just for excluding the checking from other part of code and improve readability.
> > 
> 
> I think that we can have only macro instead of the function nilfs_check_ondisk_sizes().
> And this macros can be placed in the begin of main() call. I think that it will be enough
> for the compilation phase check.

Ah, I see.

> 
> >> 
> >> I suppose that we need to have some run-time check anyway. Your approach
> >> is correct for the current state of the code. But I feel a necessity in run-time check
> >> anyway. Maybe it looks like a paranoia. :) Maybe it needs to extend checking
> >> in this place.
> > 
> > Do you mean both of the build time check and the run time check? If
> > so, I agree with your opinion. I'll send v2 based on this policy.
> > 
> 
> I mean that block size can be different during volume creation and maybe
> it makes sense to extend a block size related checking for run-time phase.
> That's all. But right now I haven't any concrete suggestions.

Currently, the check is comparison between sizes of important structs and the
minimal block size. So we don't need a function for it. I think adding the
function for runtime checking when nilfs requires it would be enough.

Thanks,
Hitoshi

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