rh_features: move rh_features entry to sys/kernel

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

This patch is a backport of the following RHEL-only commit:
commit f8a16e956bfc72efd4ed56d19821a1de812cb8ad
Author: Ricardo Robaina <rrobaina@redhat.com>
Date:   Fri May 10 20:31:21 2024 -0300

    rh_features: move rh_features entry to sys/kernel

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

    Conflicts:
       - register_sysctl_table() is currently deprecated, replacing it with
         register_sysctl_init()

    This patch is a backport of the following upstream commit:
    commit b42078ac845a3bfb5a6bfc621515e5a7acba510a
    Author: Hangbin Liu <haliu@redhat.com>
    Date:   Wed Nov 13 13:54:23 2019 -0500

        [kernel] rh_features: move rh_features entry to sys/kernel

        Message-id: <20191113135423.25652-1-haliu@redhat.com>
        Patchwork-id: 286074
        O-Subject: [RHEL8.2 net PATCHv3] rh_features: move rh_features entry to sys/kernel
        Bugzilla: 1660583
        RH-Acked-by: Ivan Vecera <ivecera@redhat.com>
        RH-Acked-by: Jiri Benc <jbenc@redhat.com>

        Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1660583
        Brew: https://brewweb.engineering.redhat.com/brew/taskinfo?taskID=24659187
        Upstream Status: RHEL only
        Test: tested with sos-3.7-7.el8_1 and we can save rh_features correctly

        In the past we put the rh_feature info to /proc/driver/rh_feature. Prarit
        ask to put this to a more suitable place. And the file needs to be picked
        up by sosreport.

        /proc/sys/kernel may not be a very good place. But since we already has the
        'tainted' file (as well as some others, e.g. osrelease or version) there,
        we can put it here before finding a more suitable place.

        v2:
        Move rh_features_show in to ifdef CONFIG_SYSCTL.
        Also as Jiri suggested:
        a) we need to check the register_sysctl_table return value.
        b) Change list_for_each_entry_rcu to list_for_each_entry_lockless in
           rh_print_used_features, which is more correct from the documentation
           point of view.

        v3:
        As Jiri remind, we may get overflow with snprintf, use scnprintf instead.

        Signed-off-by: Hangbin Liu <haliu@redhat.com>
        Signed-off-by: Timothy Redaelli <tredaelli@redhat.com>
        Signed-off-by: Bruno Meneguele <bmeneg@redhat.com>

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

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

Author: rprobaina

kernel/rh_features.c

@@ -7,6 +7,8 @@
 #include <linux/rh_features.h>
 
 #define RH_FEATURE_NAME_LEN	32
+#define MAX_RH_FEATURES		128
+#define MAX_RH_FEATURE_NAME_LEN	(MAX_RH_FEATURES * RH_FEATURE_NAME_LEN)
 
 struct rh_feature {
 	struct list_head list;
@@ -58,38 +60,56 @@ void rh_print_used_features(void)
 	if (list_empty(&rh_feature_list))
 		return;
 	printk(KERN_DEFAULT "Features:");
-	list_for_each_entry_rcu(feat, &rh_feature_list, list) {
+	list_for_each_entry_lockless(feat, &rh_feature_list, list) {
 		pr_cont(" %s", feat->name);
 	}
 	pr_cont("\n");
 }
 EXPORT_SYMBOL(rh_print_used_features);
 
-static int rh_features_show(struct seq_file *seq, void *unused)
+#ifdef CONFIG_SYSCTL
+static int rh_features_show(struct ctl_table *ctl, int write,
+			    void __user *buffer, size_t *lenp,
+			    loff_t *ppos)
 {
+	struct ctl_table tbl = { .maxlen = MAX_RH_FEATURE_NAME_LEN, };
 	struct rh_feature *feat;
-	bool space = false;
+	size_t offs = 0;
+	int ret;
+
+	tbl.data = kmalloc(tbl.maxlen, GFP_KERNEL);
+	if (!tbl.data)
+		return -ENOMEM;
 
-	if (list_empty(&rh_feature_list))
-		return 0;
 	rcu_read_lock();
 	list_for_each_entry_rcu(feat, &rh_feature_list, list) {
-		if (space)
-			seq_puts(seq, " ");
-		seq_puts(seq, feat->name);
-		space = true;
+		offs += scnprintf(tbl.data + offs, tbl.maxlen - offs, "%s%s",
+				  offs == 0 ? "" : " ", feat->name);
 	}
 	rcu_read_unlock();
-	seq_puts(seq, "\n");
-	return 0;
+
+	ret = proc_dostring(&tbl, write, buffer, lenp, ppos);
+	kfree(tbl.data);
+	return ret;
 }
 
+static struct ctl_table rh_features_table[] = {
+	{
+		.procname = "rh_features",
+		.data = &rh_feature_list,
+		.maxlen = MAX_RH_FEATURE_NAME_LEN,
+		.mode = 0444,
+		.proc_handler = rh_features_show,
+	},
+	{ }
+};
+#endif
+
 static __init int rh_features_init(void)
 {
-	struct proc_dir_entry *ent;
-
-	ent = proc_create_single("driver/rh_features", 0, NULL, rh_features_show);
-	WARN_ON(!ent);
+#ifdef CONFIG_SYSCTL
+	register_sysctl_init("kernel", rh_features_table);
+#endif
 	return 0;
 }
 subsys_initcall(rh_features_init);