Linux Virtualization - Jan 2017 - [PATCH] vhost: scsi: constify target_core_fabric_ops structures

On Tue, Jan 10, 2017 at 10:41 AM, Michael S. Tsirkin <mst at redhat.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 at p={...};
>>
>> @ok@
>> position p;
>> identifier r.i;
>> @@
>> (
>> target_register_template(&i at p)
>> |
>> target_unregister_template(&i at p)
>> )
>> @bad@
>> position p!={r.p,ok.p};
>> identifier r.i;
>> @@
>> i at 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
>
>> Signed-off-by: Bhumika Goyal <bhumirks at gmail.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

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 at
redhat.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 at p={...};
> >>
> >> @ok@
> >> position p;
> >> identifier r.i;
> >> @@
> >> (
> >> target_register_template(&i at p)
> >> |
> >> target_unregister_template(&i at p)
> >> )
> >> @bad@
> >> position p!={r.p,ok.p};
> >> identifier r.i;
> >> @@
> >> i at 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 at gmail.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