netdev - Re: [PATCH] vhost: scsi: constify target_core_fabric

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Date:   Tue, 10 Jan 2017 17:13:27 +0200
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Bhumika Goyal <bhumirks@...il.com>
Cc:     Julia Lawall <julia.lawall@...6.fr>, jasowang@...hat.com,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vhost: scsi: constify target_core_fabric_ops structures

On Tue, Jan 10, 2017 at 06:11:25PM +0530, Bhumika Goyal wrote:
> On Tue, Jan 10, 2017 at 10:41 AM, Michael S. Tsirkin <mst@...hat.com> wrote:
> > On Mon, Jan 09, 2017 at 08:51:02PM +0530, Bhumika Goyal wrote:
> >> Declare target_core_fabric_ops strucrues as const as they are only
> >> passed as an argument to the functions target_register_template and
> >> target_unregister_template. The arguments are of type const struct
> >> target_core_fabric_ops *, so target_core_fabric_ops structures having
> >> this property can be declared const.
> >> Done using Coccinelle:
> >>
> >> @r disable optional_qualifier@
> >> identifier i;
> >> position p;
> >> @@
> >> static struct target_core_fabric_ops i@......};
> >>
> >> @ok@
> >> position p;
> >> identifier r.i;
> >> @@
> >> (
> >> target_register_template(&i@p)
> >> |
> >> target_unregister_template(&i@p)
> >> )
> >> @bad@
> >> position p!={r.p,ok.p};
> >> identifier r.i;
> >> @@
> >> i@p
> >>
> >> @depends on !bad disable optional_qualifier@
> >> identifier r.i;
> >> @@
> >> +const
> >> struct target_core_fabric_ops i;
> >>
> >> File size before: drivers/vhost/scsi.o
> >>    text          data     bss     dec     hex filename
> >>   18063          2985      40   21088    5260 drivers/vhost/scsi.o
> >>
> >> File size after: drivers/vhost/scsi.o
> >>    text          data     bss     dec     hex filename
> >>   18479          2601      40   21120    5280 drivers/vhost/scsi.o
> >
> > What are these numbers trying to prove?
> >
> 
> These numbers show that adding const has decreased the size of the
> data segment and increased the size of the text segment, suggesting
> that the changed code has been compiled and the const annotation has
> had an effect.
> 
> Thanks,
> Bhumika

I wonder why there's a net increase in memory consumption though.


> >
> >> Signed-off-by: Bhumika Goyal <bhumirks@...il.com>
> >> ---
> >>  drivers/vhost/scsi.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
> >> index 253310c..620366d 100644
> >> --- a/drivers/vhost/scsi.c
> >> +++ b/drivers/vhost/scsi.c
> >> @@ -2087,7 +2087,7 @@ static void vhost_scsi_drop_tport(struct se_wwn *wwn)
> >>       NULL,
> >>  };
> >>
> >> -static struct target_core_fabric_ops vhost_scsi_ops = {
> >> +static const struct target_core_fabric_ops vhost_scsi_ops = {
> >>       .module                         = THIS_MODULE,
> >>       .name                           = "vhost",
> >>       .get_fabric_name                = vhost_scsi_get_fabric_name,
> >
> > If it can be const it probably should ...
> >
> >> --
> >> 1.9.1