Re: [PATCH 2/2] include/uapi pps.h: drop not needed PPS_MAX_SOURCES define

From: Rodolfo Giometti
Date: Fri Jun 30 2023 - 09:30:08 EST


On 30/06/23 14:53, Greg Kroah-Hartman wrote:
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@xxxxxxxxxxxx>
---
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 :)

I'm puzzled since I did as you say... patch 1/2 increases PPS_MAX_SOURCES value while patch 2/2 drops PPS_MAX_SOURCES define.

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.

It's true, but well written PPS clients should relay only on PPS API which in turn doesn't states that define. :P

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

If you think that patch 2 is not good, no problem, just drop it, but please just consider applying patch 1, since increasing PPS_MAX_SOURCES value is good.

Ciao,

Rodolfo

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