linux-kernel - RE: [PATCH] staging: lustre: ldlm: use designated initializers

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Message-ID: <C6D48C5819337145905EDC9DB164E69728D44FEC@fmsmsx120.amr.corp.intel.com>
Date:   Tue, 20 Dec 2016 14:57:17 +0000
From:   "Hammond, John" <john.hammond@...el.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>,
        Bruce Korb <bruce.korb@...il.com>
CC:     James Simmons <jsimmons@...radead.org>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        "Dilger, Andreas" <andreas.dilger@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Faccini, Bruno" <bruno.faccini@...el.com>,
        "Drokin, Oleg" <oleg.drokin@...el.com>,
        Vitaly Fertman <vitaly_fertman@...atex.com>,
        "Liu, Emoly" <emoly.liu@...el.com>,
        "Lustre Development List" <lustre-devel@...ts.lustre.org>
Subject: RE: [PATCH] staging: lustre: ldlm: use designated initializers

> On Mon, Dec 19, 2016 at 08:47:50AM -0800, Bruce Korb wrote:
> > On Mon, Dec 19, 2016 at 8:22 AM, James Simmons
> > >> --- a/drivers/staging/lustre/lustre/ldlm/ldlm_flock.c
> > >> +++ b/drivers/staging/lustre/lustre/ldlm/ldlm_flock.c
> > >> @@ -143,7 +143,7 @@ static int ldlm_process_flock_lock(struct ldlm_lock
> *req, __u64 *flags,
> > >>       int added = (mode == LCK_NL);
> > >>       int overlaps = 0;
> > >>       int splitted = 0;
> > >> -     const struct ldlm_callback_suite null_cbs = { NULL };
> > >> +     const struct ldlm_callback_suite null_cbs = { };
> > >>
> > >>       CDEBUG(D_DLMTRACE,
> > >>              "flags %#llx owner %llu pid %u mode %u start %llu end
> > >> %llu\n",
> > >
> > > Nak. Filling null_cbs with random data is a bad idea. If you look at
> > > ldlm_lock_create() where this is used you have
> > >
> > > if (cbs) {
> > >         lock->l_blocking_ast = cbs->lcs_blocking;
> > >         lock->l_completion_ast = cbs->lcs_completion;
> > >         lock->l_glimpse_ast = cbs->lcs_glimpse; }
> > >
> > > Having lock->l_* point to random addresses is a bad idea.
> > > What really needs to be done is proper initialization of that
> > > structure. A bunch of patches will be coming to address this.
> >
> > I'm not understanding the effect of the original difference.  If you
> > specify any initializer, then all fields not specified are filled with
> > zero bits. Any pointers are, perforce, NULL.  That should make both "{
> > NULL }" and "{}" equivalent.
> 
> They are equivalent, yes, but people want to use a GCC plugin that randomizes
> struct layouts for internal structures and the plugin doesn't work when you use
> struct ordering to initialize the struct.  The plugin requires that you use
> designated intializers.

"{ NULL }" is valid ISO C, but unfortunately "{}" is not.