linux-kernel - Re: [PATCH] ipc: Convert ipcs

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Date:   Sat, 18 Apr 2020 14:34:51 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Manfred Spraul <manfred@...orfullife.com>,
        Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [PATCH] ipc: Convert ipcs_idr to XArray

On Sat, Apr 18, 2020 at 01:15:09PM -0700, Andrew Morton wrote:
> > --- a/ipc/util.c
> > +++ b/ipc/util.c
> > @@ -104,12 +104,20 @@ static const struct rhashtable_params ipc_kht_params = {
> >  	.automatic_shrinking	= true,
> >  };
> >  
> > +#ifdef CONFIG_CHECKPOINT_RESTORE
> 
> The code grew a few additional CONFIG_CHECKPOINT_RESTORE ifdefs. 
> What's going on here?  Why is CRIU special in ipc/?

"grew a few"?  I added (this) one and deleted two others.  From in the
middle of functions, like we usually prefer.

I mean, this is why we need something like this:

@@ -17,11 +17,11 @@ struct ipc_ids {
...
 #ifdef CONFIG_CHECKPOINT_RESTORE
-       int next_id;
+       int restore_id;
 #endif

> > +#define set_restore_id(ids, x)	ids->restore_id = x
> > +#define get_restore_id(ids)	ids->restore_id
> > +#else
> > +#define set_restore_id(ids, x)	do { } while (0)
> > +#define get_restore_id(ids)	(-1)
> > +#endif
> 
> Well these are ugly.  Can't all this be done in C?

Would you rather see it done as:

static inline void set_restore_id(struct ipc_ids *ids, int id)
{
#ifdef CONFIG_CHECKPOINT_RESTORE
	ids->restore_id = id;
#endif
}

static inline int get_restore_id(struct ipc_ids *ids)
{
#ifdef CONFIG_CHECKPOINT_RESTORE
	return ids->restore_id;
#else
	return -1;
#endif
}