[PATCH 0/25] Replace DEFINE_PCI_DEVICE_TABLE macro use

[PATCH 0/25] Replace DEFINE_PCI_DEVICE_TABLE macro use

[Benoit Taine]

We should prefer `const struct pci_device_id` over
`DEFINE_PCI_DEVICE_TABLE` to meet kernel coding style guidelines.
This issue was reported by checkpatch.

A simplified version of the semantic patch that makes this change is as
follows (http://coccinelle.lip6.fr/):

// <smpl>

@@
identifier i;
declarer name DEFINE_PCI_DEVICE_TABLE;
initializer z;
@@

- DEFINE_PCI_DEVICE_TABLE(i)
+ const struct pci_device_id i[]
= z;

// </smpl>

I have 103 patches ready, and will only send a few for you to judge if
it is useful enough, and to prevent from spamming too much.

Thanks.

Re: [PATCH 0/25] Replace DEFINE_PCI_DEVICE_TABLE macro use

[John W. Linville]

On Fri, Jul 18, 2014 at 05:26:47PM +0200, Benoit Taine wrote:
> We should prefer `const struct pci_device_id` over
> `DEFINE_PCI_DEVICE_TABLE` to meet kernel coding style guidelines.
> This issue was reported by checkpatch.

Honestly, I prefer the macro -- it stands-out more.  Maybe the style
guidelines and/or checkpatch should change instead?

John
-- 
John W. Linville		Someday the world will need a hero, and you
linville@tuxdriver.com			might be all we have.  Be ready.

Re: [PATCH 0/25] Replace DEFINE_PCI_DEVICE_TABLE macro use

[Greg KH]

On Fri, Jul 18, 2014 at 12:22:13PM -0400, John W. Linville wrote:
> On Fri, Jul 18, 2014 at 05:26:47PM +0200, Benoit Taine wrote:
> > We should prefer `const struct pci_device_id` over
> > `DEFINE_PCI_DEVICE_TABLE` to meet kernel coding style guidelines.
> > This issue was reported by checkpatch.
> 
> Honestly, I prefer the macro -- it stands-out more.  Maybe the style
> guidelines and/or checkpatch should change instead?

The macro is horrid, no other bus has this type of thing just to save a
few characters in typing, so why should PCI be "special" in this regard
anymore?

thanks,

greg k-h

Re: [PATCH 0/25] Replace DEFINE_PCI_DEVICE_TABLE macro use

[James Bottomley]

On Fri, 2014-07-18 at 09:43 -0700, Greg KH wrote:
> On Fri, Jul 18, 2014 at 12:22:13PM -0400, John W. Linville wrote:
> > On Fri, Jul 18, 2014 at 05:26:47PM +0200, Benoit Taine wrote:
> > > We should prefer `const struct pci_device_id` over
> > > `DEFINE_PCI_DEVICE_TABLE` to meet kernel coding style guidelines.
> > > This issue was reported by checkpatch.
> > 
> > Honestly, I prefer the macro -- it stands-out more.  Maybe the style
> > guidelines and/or checkpatch should change instead?
> 
> The macro is horrid, no other bus has this type of thing just to save a
> few characters in typing

OK, so this is the macro:

#define DEFINE_PCI_DEVICE_TABLE(_table) \
	const struct pci_device_id _table[]

Could you explain what's so horrible?

The reason it's useful today is that people forget the const (and
sometimes the [] making it a true table instead of a pointer).  If you
use the DEFINE_PCI_DEVICE_TABLE macro, the compile breaks if you use it
wrongly (good) and you automatically get the correct annotations.

> , so why should PCI be "special" in this regard
> anymore?

I think the PCI usage dwarfs most other bus types now, so you could turn
the question around.  However, I don't think majority voting is a good
guide to best practise; lets debate the merits for their own sake.

James

Re: [PATCH 0/25] Replace DEFINE_PCI_DEVICE_TABLE macro use

[Greg KH]

On Fri, Jul 18, 2014 at 09:54:32AM -0700, James Bottomley wrote:
> On Fri, 2014-07-18 at 09:43 -0700, Greg KH wrote:
> > On Fri, Jul 18, 2014 at 12:22:13PM -0400, John W. Linville wrote:
> > > On Fri, Jul 18, 2014 at 05:26:47PM +0200, Benoit Taine wrote:
> > > > We should prefer `const struct pci_device_id` over
> > > > `DEFINE_PCI_DEVICE_TABLE` to meet kernel coding style guidelines.
> > > > This issue was reported by checkpatch.
> > > 
> > > Honestly, I prefer the macro -- it stands-out more.  Maybe the style
> > > guidelines and/or checkpatch should change instead?
> > 
> > The macro is horrid, no other bus has this type of thing just to save a
> > few characters in typing
> 
> OK, so this is the macro:
> 
> #define DEFINE_PCI_DEVICE_TABLE(_table) \
> 	const struct pci_device_id _table[]
> 
> Could you explain what's so horrible?
> 
> The reason it's useful today is that people forget the const (and
> sometimes the [] making it a true table instead of a pointer).  If you
> use the DEFINE_PCI_DEVICE_TABLE macro, the compile breaks if you use it
> wrongly (good) and you automatically get the correct annotations.

We have almost 1000 more uses of the non-macro version than the "macro"
version in the kernel today:
$ git grep -w DEFINE_PCI_DEVICE_TABLE | wc -l
262
$ git grep "const struct pci_device_id" | wc -l
1254

My big complaint is that we need to be consistant, either pick one or
the other and stick to it.  As the macro is the least used, it's easiest
to fix up, and it also is more consistant with all other kernel
subsystems which do not have such a macro.

As there is no need for the __init macro mess anymore, there's no real
need for the DEFINE_PCI_DEVICE_TABLE macro either.  I think checkpatch
will catch the use of non-const users for the id table already today, it
catches lots of other uses like this already.

> > , so why should PCI be "special" in this regard
> > anymore?
> 
> I think the PCI usage dwarfs most other bus types now, so you could turn
> the question around.  However, I don't think majority voting is a good
> guide to best practise; lets debate the merits for their own sake.

Not really "dwarf", USB is close with over 700 such structures:
$ git grep "const struct usb_device_id" | wc -l
725

And i2c is almost just as big as PCI:
$ git grep "const struct i2c_device_id" | wc -l
1223

So again, this macro is not consistent with the majority of PCI drivers,
nor with any other type of "device id" declaration in the kernel, which
is why I feel it should be removed.

And finally, the PCI documentation itself says to not use this macro, so
this isn't a "new" thing.  From Documentation/PCI/pci.txt:

	The ID table is an array of struct pci_device_id entries ending with an
	all-zero entry.  Definitions with static const are generally preferred.
	Use of the deprecated macro DEFINE_PCI_DEVICE_TABLE should be avoided.

That wording went into the file last December, when we last talked about
this and everyone in that discussion agreed to remove the macro for the
above reasons.

Consistency matters.

thanks,

greg k-h

Re: [PATCH 0/25] Replace DEFINE_PCI_DEVICE_TABLE macro use

[James Bottomley]

On Fri, 2014-07-18 at 11:17 -0700, Greg KH wrote:
> On Fri, Jul 18, 2014 at 09:54:32AM -0700, James Bottomley wrote:
> > On Fri, 2014-07-18 at 09:43 -0700, Greg KH wrote:
> > > On Fri, Jul 18, 2014 at 12:22:13PM -0400, John W. Linville wrote:
> > > > On Fri, Jul 18, 2014 at 05:26:47PM +0200, Benoit Taine wrote:
> > > > > We should prefer `const struct pci_device_id` over
> > > > > `DEFINE_PCI_DEVICE_TABLE` to meet kernel coding style guidelines.
> > > > > This issue was reported by checkpatch.
> > > > 
> > > > Honestly, I prefer the macro -- it stands-out more.  Maybe the style
> > > > guidelines and/or checkpatch should change instead?
> > > 
> > > The macro is horrid, no other bus has this type of thing just to save a
> > > few characters in typing
> > 
> > OK, so this is the macro:
> > 
> > #define DEFINE_PCI_DEVICE_TABLE(_table) \
> > 	const struct pci_device_id _table[]
> > 
> > Could you explain what's so horrible?
> > 
> > The reason it's useful today is that people forget the const (and
> > sometimes the [] making it a true table instead of a pointer).  If you
> > use the DEFINE_PCI_DEVICE_TABLE macro, the compile breaks if you use it
> > wrongly (good) and you automatically get the correct annotations.
> 
> We have almost 1000 more uses of the non-macro version than the "macro"
> version in the kernel today:
> $ git grep -w DEFINE_PCI_DEVICE_TABLE | wc -l
> 262
> $ git grep "const struct pci_device_id" | wc -l
> 1254
> 
> My big complaint is that we need to be consistant, either pick one or
> the other and stick to it.  As the macro is the least used, it's easiest
> to fix up, and it also is more consistant with all other kernel
> subsystems which do not have such a macro.

I've a weak preference for consistency, but not at the expense of
hundreds of patches churning the kernel to remove an innocuous macro.
Churn costs time and effort.

> As there is no need for the __init macro mess anymore, there's no real
> need for the DEFINE_PCI_DEVICE_TABLE macro either.  I think checkpatch
> will catch the use of non-const users for the id table already today, it
> catches lots of other uses like this already.
> 
> > > , so why should PCI be "special" in this regard
> > > anymore?
> > 
> > I think the PCI usage dwarfs most other bus types now, so you could turn
> > the question around.  However, I don't think majority voting is a good
> > guide to best practise; lets debate the merits for their own sake.
> 
> Not really "dwarf", USB is close with over 700 such structures:
> $ git grep "const struct usb_device_id" | wc -l
> 725
> 
> And i2c is almost just as big as PCI:
> $ git grep "const struct i2c_device_id" | wc -l
> 1223
> 
> So again, this macro is not consistent with the majority of PCI drivers,
> nor with any other type of "device id" declaration in the kernel, which
> is why I feel it should be removed.
> 
> And finally, the PCI documentation itself says to not use this macro, so
> this isn't a "new" thing.  From Documentation/PCI/pci.txt:
> 
> 	The ID table is an array of struct pci_device_id entries ending with an
> 	all-zero entry.  Definitions with static const are generally preferred.
> 	Use of the deprecated macro DEFINE_PCI_DEVICE_TABLE should be avoided.
> 
> That wording went into the file last December, when we last talked about
> this and everyone in that discussion agreed to remove the macro for the
> above reasons.
> 
> Consistency matters.

In this case, I don't think it does that much ... a cut and paste either
way (from a macro or non-macro based driver) yields correct code.  Since
there's no bug here and no apparent way to misuse the macro, why bother?

Anyway, it's PCI code ... let the PCI maintainer decide.  However, if he
does want this do it as one big bang patch via either the PCI or Trivial
tree (latter because Jiří has experience doing this, but the former
might be useful so the decider feels the pain ...)

James

Re: [PATCH 0/25] Replace DEFINE_PCI_DEVICE_TABLE macro use

[Joe Perches]

On Fri, 2014-07-18 at 09:43 -0700, Greg KH wrote:
> On Fri, Jul 18, 2014 at 12:22:13PM -0400, John W. Linville wrote:
> > On Fri, Jul 18, 2014 at 05:26:47PM +0200, Benoit Taine wrote:
> > > We should prefer `const struct pci_device_id` over
> > > `DEFINE_PCI_DEVICE_TABLE` to meet kernel coding style guidelines.
> > > This issue was reported by checkpatch.
> >  scripts/checkpatch.pl | 4 ++--
> > Honestly, I prefer the macro -- it stands-out more.  Maybe the style
> > guidelines and/or checkpatch should change instead?
> 
> The macro is horrid, no other bus has this type of thing just to save a
> few characters in typing, so why should PCI be "special" in this regard
> anymore?

I think it doesn't matter much.

The PCI_DEVICE and PCI_VDEVICE macro uses are somewhat similar
and are frequently used with PCI_DEVICE_TABLE, so there's some
commonality there.

The checkpatch message could be made --strict/CHK instead of
WARN so most people would never see it.

Of course it could be removed altogether too.  I don't care.
---
(suggested patch is for -next)

 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index dc72a9b..754fbf2 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -3018,8 +3018,8 @@ sub process {
 
 # check for uses of DEFINE_PCI_DEVICE_TABLE
 		if ($line =~ /\bDEFINE_PCI_DEVICE_TABLE\s*\(\s*(\w+)\s*\)\s*=/) {
-			if (WARN("DEFINE_PCI_DEVICE_TABLE",
-				 "Prefer struct pci_device_id over deprecated DEFINE_PCI_DEVICE_TABLE\n" . $herecurr) &&
+			if (CHK("DEFINE_PCI_DEVICE_TABLE",
+				"Prefer struct pci_device_id over deprecated DEFINE_PCI_DEVICE_TABLE\n" . $herecurr) &&
 			    $fix) {
 				$fixed[$fixlinenr] =~ s/\b(?:static\s+|)DEFINE_PCI_DEVICE_TABLE\s*\(\s*(\w+)\s*\)\s*=\s*/static const struct pci_device_id $1\[\] = /;
 			}

Re: [PATCH 0/25] Replace DEFINE_PCI_DEVICE_TABLE macro use

[James Bottomley]

On Fri, 2014-07-18 at 17:26 +0200, Benoit Taine wrote:
> We should prefer `const struct pci_device_id` over
> `DEFINE_PCI_DEVICE_TABLE` to meet kernel coding style guidelines.
> This issue was reported by checkpatch.

What kernel coding style?  checkpatch isn't the arbiter of style, if
that's the only problem.

The DEFINE_PCI macro was a well reasoned addition when it was added in
2008.  The problem was most people were getting the definition wrong.
When we converted away from CONFIG_HOTPLUG, having this DEFINE_ meant
that only one place needed changing instead of hundreds for PCI tables.

The reason people were getting the PCI table wrong was mostly the init
section specifiers which are now gone, but it has enough underlying
utility (mostly constification) that I don't think we'd want to churn
the kernel hugely to make a change to struct pci_table and then have to
start detecting and fixing misuses.

James

Re: [PATCH 0/25] Replace DEFINE_PCI_DEVICE_TABLE macro use

[David Miller]

From: Benoit Taine <benoit.taine@lip6.fr>
Date: Fri, 18 Jul 2014 17:26:47 +0200

> We should prefer `const struct pci_device_id` over
> `DEFINE_PCI_DEVICE_TABLE` to meet kernel coding style guidelines.
> This issue was reported by checkpatch.
> 
> A simplified version of the semantic patch that makes this change is as
> follows (http://coccinelle.lip6.fr/):
> 
> // <smpl>
> 
> @@
> identifier i;
> declarer name DEFINE_PCI_DEVICE_TABLE;
> initializer z;
> @@
> 
> - DEFINE_PCI_DEVICE_TABLE(i)
> + const struct pci_device_id i[]
> = z;
> 
> // </smpl>
> 
> I have 103 patches ready, and will only send a few for you to judge if
> it is useful enough, and to prevent from spamming too much.

I'm fine with this wrt. the networking changes, but I don't think this should
be merged via my tree.