Ocfs2 devel - May 2020 - [PATCH 01/13] sysctl: add new register_sysctl_subdir() helper

Often enough all we need to do is create a subdirectory so that
we can stuff sysctls underneath it. However, *if* that directory
was already created early on the boot sequence we really have no
need to use the full boiler plate code for it, we can just use
local variables to help us guide sysctl to place the new leaf files.

So use a helper to do precisely this.

Signed-off-by: Luis Chamberlain <mcgrof at kernel.org>
---
 include/linux/sysctl.h | 11 +++++++++++
 kernel/sysctl.c        | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index ddaa06ddd852..58bc978d4f03 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -205,6 +205,9 @@ void unregister_sysctl_table(struct ctl_table_header *
table);
 extern int sysctl_init(void);
 extern void register_sysctl_init(const char *path, struct ctl_table *table,
 				 const char *table_name);
+extern struct ctl_table_header *register_sysctl_subdir(const char *base,
+						       const char *subdir,
+						       struct ctl_table *table);
 void do_sysctl_args(void);
 
 extern int pwrsw_enabled;
@@ -223,6 +226,14 @@ static inline struct ctl_table_header
*register_sysctl_table(struct ctl_table *
 	return NULL;
 }
 
+static
+inline struct ctl_table_header *register_sysctl_subdir(const char *base,
+						       const char *subdir,
+						       struct ctl_table *table)
+{
+	return NULL;
+}
+
 static inline struct ctl_table_header *register_sysctl_paths(
 			const struct ctl_path *path, struct ctl_table *table)
 {
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 008ac0576ae5..04ff032f2863 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -3195,6 +3195,43 @@ void __init register_sysctl_init(const char *path, struct
ctl_table *table,
 	}
 	kmemleak_not_leak(hdr);
 }
+
+struct ctl_table_header *register_sysctl_subdir(const char *base,
+						const char *subdir,
+						struct ctl_table *table)
+{
+	struct ctl_table_header *hdr = NULL;
+	struct ctl_table subdir_table[] = {
+		{
+			.procname	= subdir,
+			.mode		= 0555,
+			.child		= table,
+		},
+		{ }
+	};
+	struct ctl_table base_table[] = {
+		{
+			.procname	= base,
+			.mode		= 0555,
+			.child		= subdir_table,
+		},
+		{ }
+	};
+
+	if (!table->procname)
+		goto out;
+
+	hdr = register_sysctl_table(base_table);
+	if (unlikely(!hdr)) {
+		pr_err("failed when creating subdirectory sysctl %s/%s/%s\n",
+		       base, subdir, table->procname);
+		goto out;
+	}
+	kmemleak_not_leak(hdr);
+out:
+	return hdr;
+}
+EXPORT_SYMBOL_GPL(register_sysctl_subdir);
 #endif /* CONFIG_SYSCTL */
 /*
  * No sense putting this after each symbol definition, twice,
-- 
2.26.2

On Fri, 29 May 2020, Luis Chamberlain <mcgrof at kernel.org>
wrote:
> Often enough all we need to do is create a subdirectory so that
> we can stuff sysctls underneath it. However, *if* that directory
> was already created early on the boot sequence we really have no
> need to use the full boiler plate code for it, we can just use
> local variables to help us guide sysctl to place the new leaf files.
I find it hard to figure out the lifetime requirements for the tables
passed in; when it's okay to use local variables and when you need
longer lifetimes. It's not documented, everyone appears to be using
static tables for this. It's far from obvious.

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Graphics Center

Luis Chamberlain <mcgrof at kernel.org> writes:
> Often enough all we need to do is create a subdirectory so that
> we can stuff sysctls underneath it. However, *if* that directory
> was already created early on the boot sequence we really have no
> need to use the full boiler plate code for it, we can just use
> local variables to help us guide sysctl to place the new leaf files.
>
> So use a helper to do precisely this.
Reset restart.  This is patch is total nonsense.

- You are using register_sysctl_table which as I believe I have
  mentioned is a deprecated compatibility wrapper.  The point of
  spring house cleaning is to get off of the deprecated functions
  isn't it?

- You are using the old nasty form for creating directories instead
  of just passing in a path.

- None of this is even remotely necessary.  The directories
  are created automatically if you just register their entries.

Eric