sysctl: Group proc_handler declarations and document

Make four groups in the sysctl header and document each group with an
example of how to use them.
1. proc_handler : All functions that can be passed to the proc_handler
   pointer in ctl_table
2. proc handler aggregators: Functions to create proc handlers with
   custom converters
3. bi-directional converters: Functions to create read/write custom
   converters. Can be passed to proc handler aggregators
4. uni-directional converters: Functions to create read or write custom
   converters. Can be passed as args to bi-directional converters

Use just one naming convention in the declarations: 'write' becomes
'dir' and 'buffer' becomes 'buf'.

Signed-off-by: Joel Granados <joel.granados@kernel.org>

1 files changed, 86 insertions, 40 deletions

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 8f8e357b1f4d..ad268dfd9e79 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -74,63 +74,109 @@ extern const int sysctl_vals[];
 
 extern const unsigned long sysctl_long_vals[];
 
-typedef int proc_handler(const struct ctl_table *ctl, int write, void *buffer,
-		size_t *lenp, loff_t *ppos);
-
-int proc_dostring(const struct ctl_table *, int, void *, size_t *, loff_t *);
-int proc_dobool(const struct ctl_table *table, int write, void *buffer,
-		size_t *lenp, loff_t *ppos);
+typedef int proc_handler(const struct ctl_table *ctl, int dir, void *buf,
+			 size_t *lenp, loff_t *ppos);
 
-int proc_dointvec(const struct ctl_table *, int, void *, size_t *, loff_t *);
-int proc_dointvec_minmax(const struct ctl_table *table, int dir, void *buffer,
+/* proc_handler functions */
+int proc_dostring(const struct ctl_table *ctl, int dir, void *buf, size_t *lenp,
+		  loff_t *ppos);
+int proc_dobool(const struct ctl_table *ctl, int dir, void *buf, size_t *lenp,
+		loff_t *ppos);
+int proc_dointvec(const struct ctl_table *ctl, int dir, void *buf, size_t *lenp,
+		  loff_t *ppos);
+int proc_dointvec_minmax(const struct ctl_table *ctl, int dir, void *buf,
+			 size_t *lenp, loff_t *ppos);
+int proc_douintvec(const struct ctl_table *ctl, int dir, void *buf, size_t *lenp,
+		   loff_t *ppos);
+int proc_douintvec_minmax(const struct ctl_table *ctl, int dir, void *buf,
+			  size_t *lenp, loff_t *ppos);
+int proc_dou8vec_minmax(const struct ctl_table *ctl, int dir, void *buf,
+			size_t *lenp, loff_t *ppos);
+int proc_doulongvec_minmax(const struct ctl_table *ctl, int dir, void *buf,
+			   size_t *lenp, loff_t *ppos);
+int proc_do_large_bitmap(const struct ctl_table *ctl, int dir, void *buf,
 			 size_t *lenp, loff_t *ppos);
-int proc_dointvec_conv(const struct ctl_table *table, int dir, void *buffer,
+int proc_do_static_key(const struct ctl_table *ctl, int dir, void *buf,
+		       size_t *lenp, loff_t *ppos);
+
+/*
+ * proc_handler aggregators
+ *
+ * Create a proc_handler with a custom converter. Use when the user space
+ * value is a transformation of the kernel value. Cannot be passed as
+ * proc_handlers.
+ *
+ * Example of creating your custom proc handler:
+ * int custom_converter(bool *negp, ulong *u_ptr, uint *k_ptr,
+ *                      int dir, const struct ctl_table *ctl) {...}
+ * int custom_proc_handler(const struct ctl_table *ctl, int dir,
+ *                         void *buf, size_t *lenp, loff_t *ppos
+ * { return proc_dointvec_conv(ctl, dir, buf, lenp, ppos, custom_converter); }
+ */
+int proc_dointvec_conv(const struct ctl_table *ctl, int dir, void *buf,
 		       size_t *lenp, loff_t *ppos,
 		       int (*conv)(bool *negp, unsigned long *u_ptr, int *k_ptr,
-				   int dir, const struct ctl_table *table));
-int proc_int_k2u_conv_kop(ulong *u_ptr, const int *k_ptr, bool *negp,
-			  ulong (*k_ptr_op)(const ulong));
-int proc_int_u2k_conv_uop(const ulong *u_ptr, int *k_ptr, const bool *negp,
-			  ulong (*u_ptr_op)(const ulong));
+				   int dir, const struct ctl_table *ctl));
+int proc_douintvec_conv(const struct ctl_table *ctl, int dir, void *buf,
+			size_t *lenp, loff_t *ppos,
+			int (*conv)(bool *negp, ulong *u_ptr, uint *k_ptr,
+				    int dir, const struct ctl_table *ctl));
+int proc_doulongvec_minmax_conv(const struct ctl_table *ctl, int dir, void *buf,
+				size_t *lenp, loff_t *ppos,
+				int (*conv)(bool *negp, ulong *u_ptr, ulong *k_ptr,
+					    int dir, const struct ctl_table *ctl));
+
+/*
+ * bi-directional converter functions
+ *
+ * Specify the converter function for both directions (user to kernel & kernel
+ * to user). Use when you want to change the value of the variable before
+ * assignment. Used to create custom proc_handler aggregators.
+ *
+ * Example of creating your custom bi-directional converter:
+ * int custom_u2k(ulong *u_ptr, const uint *k_ptr) { ... }
+ * int custom_converter(bool *negp, ulong *u_ptr, uint *k_ptr,
+ *                      int dir, const struct ctl_table *ctl)
+ * { return proc_uint_conv(u_ptr, k_ptr, dir, ctl, true,
+ *                         custom_u2k, proc_uint_k2u_conv}
+ */
 int proc_int_conv(bool *negp, ulong *u_ptr, int *k_ptr, int dir,
 		  const struct ctl_table *tbl, bool k_ptr_range_check,
 		  int (*user_to_kern)(const bool *negp, const ulong *u_ptr, int *k_ptr),
 		  int (*kern_to_user)(bool *negp, ulong *u_ptr, const int *k_ptr));
-
-int proc_douintvec(const struct ctl_table *, int, void *, size_t *, loff_t *);
-int proc_douintvec_minmax(const struct ctl_table *table, int write, void *buffer,
-		size_t *lenp, loff_t *ppos);
-int proc_douintvec_conv(const struct ctl_table *table, int write, void *buffer,
-			size_t *lenp, loff_t *ppos,
-			int (*conv)(bool *negp, ulong *lvalp, uint *valp,
-				    int write, const struct ctl_table *table));
-int proc_uint_k2u_conv(ulong *u_ptr, const uint *k_ptr);
-int proc_uint_u2k_conv_uop(const ulong *u_ptr, uint *k_ptr,
-			   ulong (*u_ptr_op)(const ulong));
 int proc_uint_conv(ulong *u_ptr, uint *k_ptr, int dir,
 		   const struct ctl_table *tbl, bool k_ptr_range_check,
 		   int (*user_to_kern)(const ulong *u_ptr, uint *k_ptr),
 		   int (*kern_to_user)(ulong *u_ptr, const uint *k_ptr));
+int proc_ulong_conv(ulong *u_ptr, ulong *k_ptr, int dir,
+		    const struct ctl_table *tbl, bool k_ptr_range_check,
+		    int (*user_to_kern)(const ulong *u_ptr, ulong *k_ptr),
+		    int (*kern_to_user)(ulong *u_ptr, const ulong *k_ptr));
 
-int proc_dou8vec_minmax(const struct ctl_table *table, int write, void *buffer,
-			size_t *lenp, loff_t *ppos);
-int proc_doulongvec_minmax(const struct ctl_table *, int, void *, size_t *, loff_t *);
-int proc_doulongvec_minmax_conv(const struct ctl_table *table, int dir,
-				void *buffer, size_t *lenp, loff_t *ppos,
-				int (*conv)(bool *negp, ulong *u_ptr, ulong *k_ptr,
-					    int dir, const struct ctl_table *table));
-int proc_do_large_bitmap(const struct ctl_table *, int, void *, size_t *, loff_t *);
-int proc_do_static_key(const struct ctl_table *table, int write, void *buffer,
-		size_t *lenp, loff_t *ppos);
-
+/*
+ * uni-directional converter functions
+ *
+ * Specify the converter function for one directions (user to kernel or
+ * kernel to user). Use to call the actual value conversion. Used to Create
+ * bi-directional converters.
+ *
+ * Example of creating a uni-directional converter:
+ * ulong op(const ulong val) { ... }
+ * int custom_unidir_conv(ulong *u_ptr, const uint *k_ptr)
+ * { return proc_uint_k2u_conv_kop(u_ptr, k_ptr, op); }
+ */
+int proc_int_k2u_conv_kop(ulong *u_ptr, const int *k_ptr, bool *negp,
+			  ulong (*k_ptr_op)(const ulong));
+int proc_int_u2k_conv_uop(const ulong *u_ptr, int *k_ptr, const bool *negp,
+			  ulong (*u_ptr_op)(const ulong));
+int proc_uint_k2u_conv(ulong *u_ptr, const uint *k_ptr);
+int proc_uint_u2k_conv_uop(const ulong *u_ptr, uint *k_ptr,
+			   ulong (*u_ptr_op)(const ulong));
 int proc_ulong_u2k_conv_uop(const ulong *u_ptr, ulong *k_ptr,
 			    ulong (*u_ptr_op)(const ulong));
 int proc_ulong_k2u_conv_kop(ulong *u_ptr, const ulong *k_ptr,
 			    ulong (*k_ptr_op)(const ulong));
-int proc_ulong_conv(ulong *u_ptr, ulong *k_ptr, int dir,
-		    const struct ctl_table *tbl, bool k_ptr_range_check,
-		    int (*user_to_kern)(const ulong *u_ptr, ulong *k_ptr),
-		    int (*kern_to_user)(ulong *u_ptr, const ulong *k_ptr));
+
 /*
  * Register a set of sysctl names by calling register_sysctl
  * with an initialised array of struct ctl_table's.