linux-kernel - Re: [PATCH 2/2] include/uapi pps.h: drop not needed PPS_MAX

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Message-ID: <2023063015-immerse-broadside-3dab@gregkh>
Date:   Fri, 30 Jun 2023 14:53:14 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Rodolfo Giometti <giometti@...eenne.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] include/uapi pps.h: drop not needed PPS_MAX_SOURCES
 define

On Fri, Jun 30, 2023 at 09:50:33AM +0200, Rodolfo Giometti wrote:
> On 30/06/23 09:31, Greg Kroah-Hartman wrote:
> > On Fri, Jun 30, 2023 at 09:18:26AM +0200, Rodolfo Giometti wrote:
> > > Userspace PPS clients should not known about how many PPS sources can
> > > be defined within the system (nor the rfc2783 say so), so we can
> > > safely drop this define since is not used anymore in the kernel too.
> > > 
> > > Signed-off-by: Rodolfo Giometti <giometti@...eenne.com>
> > > ---
> > >   drivers/pps/pps.c        | 6 +++---
> > >   include/uapi/linux/pps.h | 1 -
> > >   2 files changed, 3 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c
> > > index 5d19baae6a38..1a6131608036 100644
> > > --- a/drivers/pps/pps.c
> > > +++ b/drivers/pps/pps.c
> > > @@ -354,7 +354,7 @@ int pps_register_cdev(struct pps_device *pps)
> > >   	 * Get new ID for the new PPS source.  After idr_alloc() calling
> > >   	 * the new source will be freely available into the kernel.
> > >   	 */
> > > -	err = idr_alloc(&pps_idr, pps, 0, PPS_MAX_SOURCES, GFP_KERNEL);
> > > +	err = idr_alloc(&pps_idr, pps, 0, MINORMASK, GFP_KERNEL);
> > >   	if (err < 0) {
> > >   		if (err == -ENOSPC) {
> > >   			pr_err("%s: too many PPS sources in the system\n",
> > > @@ -449,7 +449,7 @@ EXPORT_SYMBOL(pps_lookup_dev);
> > >   static void __exit pps_exit(void)
> > >   {
> > >   	class_destroy(pps_class);
> > > -	unregister_chrdev_region(pps_devt, PPS_MAX_SOURCES);
> > > +	unregister_chrdev_region(pps_devt, MINORMASK);
> > >   }
> > >   static int __init pps_init(void)
> > > @@ -463,7 +463,7 @@ static int __init pps_init(void)
> > >   	}
> > >   	pps_class->dev_groups = pps_groups;
> > > -	err = alloc_chrdev_region(&pps_devt, 0, PPS_MAX_SOURCES, "pps");
> > > +	err = alloc_chrdev_region(&pps_devt, 0, MINORMASK, "pps");
> > >   	if (err < 0) {
> > >   		pr_err("failed to allocate char device region\n");
> > >   		goto remove_class;
> > > diff --git a/include/uapi/linux/pps.h b/include/uapi/linux/pps.h
> > > index 90f2e86020ba..8a4096f18af1 100644
> > > --- a/include/uapi/linux/pps.h
> > > +++ b/include/uapi/linux/pps.h
> > > @@ -26,7 +26,6 @@
> > >   #include <linux/types.h>
> > >   #define PPS_VERSION		"5.3.6"
> > > -#define PPS_MAX_SOURCES		MINORMASK
> > 
> > Why change this in patch 1, and then delete this here?
> > 
> > That makes no sense.
> 
> I did it in two steps to be clear that the first step is about a better
> redefinition of the PPS_MAX_SOURCES define, while the second step is about
> the fact it's now that define is useless.

Better to just convert everything in patch one, and then in patch 2
delete the .h #define.  That way, when userspace breaks, you can revert
just the last patch :)

> > And if this is exported to userspace, removing it should break things,
> > right?  If not, why was it there in the first place?
> 
> In reality such define is not stated within the PPS RFC2783, so userspace
> programs whose relies on such define are broken.

RFC's do not document Linux kernel apis.

So if any userspace code breaks, you have to put this back, sorry.

thanks,

greg k-h