[PATCH net-next] ieee802154: fix variable declaration and initializer

[PATCH net-next] ieee802154: fix variable declaration and initializer

[Jean Sacren]

The commit 84dda3c648fd ("ieee802154: add support for
listen-before-talk in wpan_phy") introduced the new function
phy_set_lbt() with some minor issues in declaration and
initialization:

1) Fix the variable declaration by changing the type specifier to
   bool as that is the argument type when phy->set_lbt() is called.

2) Fix the initializer by deleting the double logical negation
   operators as they don't serve any purpose.

Signed-off-by: Jean Sacren <sakiwit@gmail.com>
Cc: Phoebe Buckheister <phoebe.buckheister@itwm.fraunhofer.de>
---
 net/ieee802154/nl-phy.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ieee802154/nl-phy.c b/net/ieee802154/nl-phy.c
index 222310a07762..643dff07803b 100644
--- a/net/ieee802154/nl-phy.c
+++ b/net/ieee802154/nl-phy.c
@@ -379,9 +379,10 @@ static int phy_set_txpower(struct wpan_phy *phy, struct genl_info *info)
 
 static int phy_set_lbt(struct wpan_phy *phy, struct genl_info *info)
 {
-	u8 on = !!nla_get_u8(info->attrs[IEEE802154_ATTR_LBT_ENABLED]);
+	bool on;
 	int rc;
 
+	on = nla_get_u8(info->attrs[IEEE802154_ATTR_LBT_ENABLED]);
 	rc = phy->set_lbt(phy, on);
 	if (rc < 0)
 		return rc;

Re: [PATCH net-next] ieee802154: fix variable declaration and initializer

[Eric Dumazet]

On Tue, 2014-03-18 at 21:19 -0600, Jean Sacren wrote:

> 2) Fix the initializer by deleting the double logical negation
>    operators as they don't serve any purpose.
> 
...
>  
>  static int phy_set_lbt(struct wpan_phy *phy, struct genl_info *info)
>  {
> -	u8 on = !!nla_get_u8(info->attrs[IEEE802154_ATTR_LBT_ENABLED]);

You do realize !!(a) is not equivalent to (a) ?





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Re: [PATCH net-next] ieee802154: fix variable declaration and initializer

[Joe Perches]

On Tue, 2014-03-18 at 20:32 -0700, Eric Dumazet wrote:
> On Tue, 2014-03-18 at 21:19 -0600, Jean Sacren wrote:
> 
> > 2) Fix the initializer by deleting the double logical negation
> >    operators as they don't serve any purpose.
> > 
> ...
> >  
> >  static int phy_set_lbt(struct wpan_phy *phy, struct genl_info *info)
> >  {
> > -	u8 on = !!nla_get_u8(info->attrs[IEEE802154_ATTR_LBT_ENABLED]);
> 
> You do realize !!(a) is not equivalent to (a) ?

It is when the type it's assigned to also changes
from u8 to bool.

I don't think it's a great style though.
I think the !! doesn't hurt here.

I'd've preferred it to be

	bool on = nla_get_u8(...)

rather than separating the declaration from the assignment
by a few lines of code.

Re: [PATCH net-next] ieee802154: fix variable declaration and initializer

[Jean Sacren]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Tue, 18 Mar 2014 20:32:21 -0700
>
> On Tue, 2014-03-18 at 21:19 -0600, Jean Sacren wrote:
> 
> > 2) Fix the initializer by deleting the double logical negation
> >    operators as they don't serve any purpose.
> > 
> ...
> >  
> >  static int phy_set_lbt(struct wpan_phy *phy, struct genl_info *info)
> >  {
> > -	u8 on = !!nla_get_u8(info->attrs[IEEE802154_ATTR_LBT_ENABLED]);
> 
> You do realize !!(a) is not equivalent to (a) ?

I admire you for your knowledge and skill. With the double logical
negation operation hereof, I do know what I'm doing.

Thank you,

-- 
Jean Sacren

Re: [PATCH net-next] ieee802154: fix variable declaration and initializer

[Eric Dumazet]

On Tue, 2014-03-18 at 20:42 -0700, Joe Perches wrote:
> On Tue, 2014-03-18 at 20:32 -0700, Eric Dumazet wrote:
> > On Tue, 2014-03-18 at 21:19 -0600, Jean Sacren wrote:
> > 
> > > 2) Fix the initializer by deleting the double logical negation
> > >    operators as they don't serve any purpose.
> > > 
> > ...
> > >  
> > >  static int phy_set_lbt(struct wpan_phy *phy, struct genl_info *info)
> > >  {
> > > -	u8 on = !!nla_get_u8(info->attrs[IEEE802154_ATTR_LBT_ENABLED]);
> > 
> > You do realize !!(a) is not equivalent to (a) ?
> 
> It is when the type it's assigned to also changes
> from u8 to bool.

I was referring to the changelog, obviously, see how I carefully
copy/pasted the relevant part ?

Stating it is a 'fix' is quite a false statement, I see no fix at all,
maybe a cleanup, but I am not really convinced.

Re: [PATCH net-next] ieee802154: fix variable declaration and initializer

[Jean Sacren]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Tue, 18 Mar 2014 21:35:54 -0700
>
> On Tue, 2014-03-18 at 20:42 -0700, Joe Perches wrote:
> > On Tue, 2014-03-18 at 20:32 -0700, Eric Dumazet wrote:
> > > On Tue, 2014-03-18 at 21:19 -0600, Jean Sacren wrote:
> > > 
> > > > 2) Fix the initializer by deleting the double logical negation
> > > >    operators as they don't serve any purpose.
> > > > 
> > > ...
> > > >  
> > > >  static int phy_set_lbt(struct wpan_phy *phy, struct genl_info *info)
> > > >  {
> > > > -	u8 on = !!nla_get_u8(info->attrs[IEEE802154_ATTR_LBT_ENABLED]);
> > > 
> > > You do realize !!(a) is not equivalent to (a) ?
> > 
> > It is when the type it's assigned to also changes
> > from u8 to bool.
> 
> I was referring to the changelog, obviously, see how I carefully
> copy/pasted the relevant part ?
> 
> Stating it is a 'fix' is quite a false statement, I see no fix at all,
> maybe a cleanup, but I am not really convinced.

Stating it is a "fix" is not a false statement at all. !! falsely
changes the value to be int TWICE for nothing! Are you still not
convinced?

-- 
Jean Sacren

Re: [PATCH net-next] ieee802154: fix variable declaration and initializer

[Joe Perches]

On Tue, 2014-03-18 at 21:35 -0700, Eric Dumazet wrote:
> On Tue, 2014-03-18 at 20:42 -0700, Joe Perches wrote:
> > On Tue, 2014-03-18 at 20:32 -0700, Eric Dumazet wrote:
> > > On Tue, 2014-03-18 at 21:19 -0600, Jean Sacren wrote:
> > > 
> > > > 2) Fix the initializer by deleting the double logical negation
> > > >    operators as they don't serve any purpose.
> > > > 
> > > ...
> > > >  
> > > >  static int phy_set_lbt(struct wpan_phy *phy, struct genl_info *info)
> > > >  {
> > > > -	u8 on = !!nla_get_u8(info->attrs[IEEE802154_ATTR_LBT_ENABLED]);
> > > 
> > > You do realize !!(a) is not equivalent to (a) ?
> > 
> > It is when the type it's assigned to also changes
> > from u8 to bool.
> 
> I was referring to the changelog, obviously, see how I carefully
> copy/pasted the relevant part ?

No, that's not obvious at all actually.

I would have used "Change the type to bool and remove
the now unnecessary !!" in the changelog to link Jean's
points 1 and 2, but your statement and the code and
commit log changes proposed by Jean don't match.

The type _did_ change as described in point 1.

> Stating it is a 'fix' is quite a false statement, I see no fix at all,
> maybe a cleanup, but I am not really convinced.

Perhaps "fix" is a more flexible word than you imagine.
Perhaps this a code style "fix" without logic change.

<shrug>  I'm very ambivalent about it too.

Re: [PATCH net-next] ieee802154: fix variable declaration and initializer

[Joe Perches]

On Tue, 2014-03-18 at 22:56 -0600, Jean Sacren wrote:
> Stating it is a "fix" is not a false statement at all. !! falsely
> changes the value to be int TWICE for nothing! Are you still not
> convinced?

Not so fast Jean.  There's no logic change.

Changing the type to bool does exactly the same thing
and doesn't change the generated object code at all.

$ diff net/ieee802154/nl-phy.lst.new net/ieee802154/nl-phy.lst.old
2289d2288
< static int phy_set_lbt(struct wpan_phy *phy, struct genl_info *info)
2291c2290
< 	u8 on = !!nla_get_u8(info->attrs[IEEE802154_ATTR_LBT_ENABLED]);
---
> 	bool on;
2293a2293
> 	on = nla_get_u8(info->attrs[IEEE802154_ATTR_LBT_ENABLED]);
2296,2298d2295
< 	return 0;
< }
< 
2301,2303c2298
< 	u8 on = !!nla_get_u8(info->attrs[IEEE802154_ATTR_LBT_ENABLED]);
<     1096:	80 78 04 00          	cmpb   $0x0,0x4(%rax)
<     109a:	41 0f 95 c5          	setne  %r13b
---
> 	bool on;
2305a2301,2303
> 	on = nla_get_u8(info->attrs[IEEE802154_ATTR_LBT_ENABLED]);
>     1096:	80 78 04 00          	cmpb   $0x0,0x4(%rax)
>     109a:	41 0f 95 c5          	setne  %r13b
2322c2320
< 
---



------------------------------------------------------------------------------
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applications. Written by three acclaimed leaders in the field,
this first edition is now available. Download your free book today!
http://p.sf.net/sfu/13534_NeoTech

Re: [PATCH net-next] ieee802154: fix variable declaration and initializer

[Eric Dumazet]

On Tue, 2014-03-18 at 22:56 -0600, Jean Sacren wrote:
> Stating it is a "fix" is not a false statement at all. !! falsely
> changes the value to be int TWICE for nothing! Are you still not
> convinced?

I think you are mistaken.

X = !!(a) makes sure X is 0 or 1.

Its a valid and useful construct.

There is no _bug_ here.