rh_flags: Rename rh_features to rh_flags

JIRA: https://issues.redhat.com/browse/RHEL-122981

Conflicts: Minor context difference due to RHEL-only commit
           c7db2ac ("kernel: Add redhat code")

This patch is a backport of the following RHEL-only commit:
commit 659bcb087790263f589f90a4b6cd75a3f2c8a89c
Author: Ricardo Robaina <rrobaina@redhat.com>
Date:   Fri May 10 20:31:21 2024 -0300

    rh_flags: Rename rh_features to rh_flags

    JIRA: https://issues.redhat.com/browse/RHEL-32987

    Conflicts:
       - Unrelated hunks dropped
       - Minor context differences due to 76106c6dac3 ('add support for rh_features')
         and d756b75a7f90 ('rh_features: move rh_features entry to sys/kernel')

    This patch is a backport of the following upstream commit:
    commit dd996f09078abf3d8a8ef1ac77616297bc77b598
    Author: Prarit Bhargava <prarit@redhat.com>
    Date:   Tue Nov 9 09:52:38 2021 -0500

        rh_flags: Rename rh_features to rh_flags

        Bugzilla: https://bugzilla.redhat.com/2021700

        Upstream Status: RHEL only

        Features implies that this code can only be used to indicate
        functionality, however, I'd like to also use these as debug flags.

        Rename rh_features to rh_flags, and change the output to indicate "Red
        Hat Flags" instead of "Features".

        Signed-off-by: Prarit Bhargava <prarit@redhat.com>

    Signed-off-by: Ricardo Robaina <rrobaina@redhat.com>

Signed-off-by: Ricardo Robaina <rrobaina@redhat.com>

Author: rprobaina

include/linux/rh_features.h

@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * rh_flags.h -- Red Hat flags tracking
+ *
+ * Copyright (c) 2018 Red Hat, Inc. -- Jiri Benc <jbenc@redhat.com>
+ *
+ * The intent of the flag tracking is to provide better and more focused
+ * support. Only those flags that are of a special interest for customer
+ * support should be tracked.
+ *
+ * THE FLAGS DO NOT EXPRESS ANY SUPPORT POLICIES.
+ */
+
+#ifndef _LINUX_RH_FLAGS_H
+#define _LINUX_RH_FLAGS_H
+
+#if defined CONFIG_RHEL_DIFFERENCES
+bool __rh_add_flag(const char *flag_name);
+void rh_print_flags(void);
+
+#define rh_add_flag(flag_name)						\
+({									\
+	static bool __mark_once __read_mostly;				\
+	bool __ret_mark_once = !__mark_once;				\
+									\
+	if (!__mark_once)						\
+		__mark_once = __rh_add_flag(flag_name);			\
+	unlikely(__ret_mark_once);					\
+})
+#else
+void rh_print_flags(void) { };
+void rh_add_flag(const char *flag_name) { };
+#endif
+#endif

include/linux/rh_flags.h

@@ -12,7 +12,7 @@ obj-y     = fork.o exec_domain.o panic.o \
 	    notifier.o ksysfs.o cred.o reboot.o \
 	    async.o range.o smpboot.o ucount.o regset.o ksyms_common.o
 
-obj-$(CONFIG_RHEL_DIFFERENCES) += rh_messages.o rh_features.o rh_shadowman.o
+obj-$(CONFIG_RHEL_DIFFERENCES) += rh_messages.o rh_flags.o rh_shadowman.o
 obj-$(CONFIG_USERMODE_DRIVER) += usermode_driver.o
 obj-$(CONFIG_MULTIUSER) += groups.o
 

kernel/Makefile

@@ -62,7 +62,7 @@
 #define CREATE_TRACE_POINTS
 #include <trace/events/module.h>
 
-#include <linux/rh_features.h>
+#include <linux/rh_flags.h>
 
 /*
  * Mutex protects:
@@ -3397,7 +3397,7 @@ void print_modules(void)
 	pr_cont("\n");
 
 #ifdef CONFIG_RHEL_DIFFERENCES
-	rh_print_used_features();
+	rh_print_flags();
 #endif
 }
 

kernel/module/main.c

@@ -0,0 +1,116 @@
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/rh_flags.h>
+
+#define RH_FLAG_NAME_LEN	32
+#define MAX_RH_FLAGS		128
+#define MAX_RH_FLAG_NAME_LEN	(MAX_RH_FLAGS * RH_FLAG_NAME_LEN)
+
+struct rh_flag {
+	struct list_head list;
+	char name[RH_FLAG_NAME_LEN];
+};
+
+static LIST_HEAD(rh_flag_list);
+static DEFINE_SPINLOCK(rh_flag_lock);
+
+bool __rh_add_flag(const char *flag_name)
+{
+	struct rh_flag *feat, *iter;
+
+	BUG_ON(in_interrupt());
+	feat = kzalloc(sizeof(*feat), GFP_ATOMIC);
+	if (WARN(!feat, "Adding Red Hat flag %s.\n", flag_name))
+		return false;
+	strscpy(feat->name, flag_name, RH_FLAG_NAME_LEN);
+
+	spin_lock(&rh_flag_lock);
+	list_for_each_entry_rcu(iter, &rh_flag_list, list) {
+		if (!strcmp(iter->name, flag_name)) {
+			kfree(feat);
+			feat = NULL;
+			break;
+		}
+	}
+	if (feat)
+		list_add_rcu(&feat->list, &rh_flag_list);
+	spin_unlock(&rh_flag_lock);
+
+	if (feat)
+		pr_info("Adding Red Hat flag %s.\n", flag_name);
+	return true;
+}
+EXPORT_SYMBOL(__rh_add_flag);
+
+void rh_print_flags(void)
+{
+	struct rh_flag *feat;
+
+	/*
+	 * This function cannot do any locking, we're oopsing. Traversing
+	 * rh_flag_list is okay, though, even without the rcu_read_lock
+	 * taken: we never delete from that list and thus don't need the
+	 * delayed free. All we need are the smp barriers invoked by the rcu
+	 * list manipulation routines.
+	 */
+	if (list_empty(&rh_flag_list))
+		return;
+	printk(KERN_DEFAULT "Red Hat flags:");
+	list_for_each_entry_lockless(feat, &rh_flag_list, list) {
+		pr_cont(" %s", feat->name);
+	}
+	pr_cont("\n");
+}
+EXPORT_SYMBOL(rh_print_flags);
+
+#ifdef CONFIG_SYSCTL
+static int rh_flags_show(struct ctl_table *ctl, int write,
+			    void __user *buffer, size_t *lenp,
+			    loff_t *ppos)
+{
+	struct ctl_table tbl = { .maxlen = MAX_RH_FLAG_NAME_LEN, };
+	struct rh_flag *feat;
+	size_t offs = 0;
+	int ret;
+
+	tbl.data = kmalloc(tbl.maxlen, GFP_KERNEL);
+	if (!tbl.data)
+		return -ENOMEM;
+	((char *)tbl.data)[0] = '\0';
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(feat, &rh_flag_list, list) {
+		offs += scnprintf(tbl.data + offs, tbl.maxlen - offs, "%s%s",
+				  offs == 0 ? "" : " ", feat->name);
+	}
+	rcu_read_unlock();
+
+	ret = proc_dostring(&tbl, write, buffer, lenp, ppos);
+	kfree(tbl.data);
+	return ret;
+}
+
+static struct ctl_table rh_flags_table[] = {
+	{
+		.procname = "rh_flags",
+		.data = &rh_flag_list,
+		.maxlen = MAX_RH_FLAG_NAME_LEN,
+		.mode = 0444,
+		.proc_handler = rh_flags_show,
+	},
+	{ }
+};
+#endif
+
+static __init int rh_flags_init(void)
+{
+#ifdef CONFIG_SYSCTL
+	register_sysctl_init("kernel", rh_flags_table);
+#endif
+	return 0;
+}
+subsys_initcall(rh_flags_init);