From 0dd0a2d3022314ae2677ed347c15e334cf307a1a Mon Sep 17 00:00:00 2001
From: Rob Norris <rob.norris@klarasystems.com>
Date: Mon, 29 Apr 2024 15:26:56 +1000
Subject: [PATCH] linux/kstat: allow multi-level module names

Module names are mapped directly to directory names in procfs, but
nothing is done to create the intermediate directories, or remove them.
This makes it impossible to sensibly present kstats about sub-objects.

This commit loops through '/'-separated names in the full module name,
creates a separate module for each, and hooks them up with a parent
pointer and child counter, and then unrolls this on the other side when
deleting a module.

Sponsored-by: Klara, Inc.
Sponsored-by: Syneto
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
---
 include/os/linux/spl/sys/kstat.h |  6 +++
 module/os/linux/spl/spl-kstat.c  | 85 ++++++++++++++++++++++++--------
 2 files changed, 70 insertions(+), 21 deletions(-)

diff --git a/include/os/linux/spl/sys/kstat.h b/include/os/linux/spl/sys/kstat.h
index 305c411ddf..7809fda520 100644
--- a/include/os/linux/spl/sys/kstat.h
+++ b/include/os/linux/spl/sys/kstat.h
@@ -20,6 +20,10 @@
  *  You should have received a copy of the GNU General Public License along
  *  with the SPL.  If not, see <http://www.gnu.org/licenses/>.
  */
+/*
+ * Copyright (c) 2024, Klara, Inc.
+ * Copyright (c) 2024, Syneto
+ */
 
 #ifndef _SPL_KSTAT_H
 #define	_SPL_KSTAT_H
@@ -89,6 +93,8 @@ typedef struct kstat_module {
 	struct list_head ksm_module_list;	/* module linkage */
 	struct list_head ksm_kstat_list;	/* list of kstat entries */
 	struct proc_dir_entry *ksm_proc;	/* proc entry */
+	struct kstat_module *ksm_parent;	/* parent module in hierarchy */
+	uint_t ksm_nchildren;			/* number of child modules */
 } kstat_module_t;
 
 typedef struct kstat_raw_ops {
diff --git a/module/os/linux/spl/spl-kstat.c b/module/os/linux/spl/spl-kstat.c
index ad553a73a6..10732d6090 100644
--- a/module/os/linux/spl/spl-kstat.c
+++ b/module/os/linux/spl/spl-kstat.c
@@ -26,6 +26,10 @@
  *  [1] https://illumos.org/man/1M/kstat
  *  [2] https://illumos.org/man/9f/kstat_create
  */
+/*
+ * Copyright (c) 2024, Klara, Inc.
+ * Copyright (c) 2024, Syneto
+ */
 
 #include <linux/seq_file.h>
 #include <sys/kstat.h>
@@ -379,33 +383,72 @@ kstat_find_module(char *name)
 	return (NULL);
 }
 
-static kstat_module_t *
-kstat_create_module(char *name)
-{
-	kstat_module_t *module;
-	struct proc_dir_entry *pde;
-
-	pde = proc_mkdir(name, proc_spl_kstat);
-	if (pde == NULL)
-		return (NULL);
-
-	module = kmem_alloc(sizeof (kstat_module_t), KM_SLEEP);
-	module->ksm_proc = pde;
-	strlcpy(module->ksm_name, name, KSTAT_STRLEN);
-	INIT_LIST_HEAD(&module->ksm_kstat_list);
-	list_add_tail(&module->ksm_module_list, &kstat_module_list);
-
-	return (module);
-
-}
-
 static void
 kstat_delete_module(kstat_module_t *module)
 {
 	ASSERT(list_empty(&module->ksm_kstat_list));
-	remove_proc_entry(module->ksm_name, proc_spl_kstat);
+	ASSERT0(module->ksm_nchildren);
+
+	kstat_module_t *parent = module->ksm_parent;
+
+	char *p = module->ksm_name, *frag;
+	while (p != NULL && (frag = strsep(&p, "/"))) {}
+
+	remove_proc_entry(frag, parent ? parent->ksm_proc : proc_spl_kstat);
 	list_del(&module->ksm_module_list);
 	kmem_free(module, sizeof (kstat_module_t));
+
+	if (parent) {
+		parent->ksm_nchildren--;
+		if (parent->ksm_nchildren == 0 &&
+		    list_empty(&parent->ksm_kstat_list))
+			kstat_delete_module(parent);
+	}
+}
+
+static kstat_module_t *
+kstat_create_module(char *name)
+{
+	char buf[KSTAT_STRLEN];
+	kstat_module_t *module, *parent;
+
+	(void) strlcpy(buf, name, KSTAT_STRLEN);
+
+	parent = NULL;
+	char *p = buf, *frag;
+	while ((frag = strsep(&p, "/")) != NULL) {
+		module = kstat_find_module(buf);
+		if (module == NULL) {
+			struct proc_dir_entry *pde = proc_mkdir(frag,
+			    parent ? parent->ksm_proc : proc_spl_kstat);
+			if (pde == NULL) {
+				cmn_err(CE_WARN, "kstat_create('%s'): "
+				    "module dir create failed", buf);
+				if (parent)
+					kstat_delete_module(parent);
+				return (NULL);
+			}
+
+			module = kmem_alloc(sizeof (kstat_module_t), KM_SLEEP);
+			module->ksm_proc = pde;
+			strlcpy(module->ksm_name, buf, KSTAT_STRLEN);
+			INIT_LIST_HEAD(&module->ksm_kstat_list);
+			list_add_tail(&module->ksm_module_list,
+			    &kstat_module_list);
+
+			if (parent != NULL) {
+				module->ksm_parent = parent;
+				parent->ksm_nchildren++;
+			}
+		}
+
+		parent = module;
+		if (p != NULL && p > frag)
+			p[-1] = '/';
+	}
+
+	return (module);
+
 }
 
 static int