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Message-Id: <20251219-jag-dovec_consolidate-v1-7-1413b92c6040@kernel.org>
Date: Fri, 19 Dec 2025 13:15:58 +0100
From: Joel Granados <joel.granados@...nel.org>
To: Kees Cook <kees@...nel.org>, Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
Joel Granados <joel.granados@...nel.org>
Subject: [PATCH 7/9] 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@...nel.org>
---
include/linux/sysctl.h | 128 +++++++++++++++++++++++++++++++++----------------
1 file changed, 87 insertions(+), 41 deletions(-)
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 8f8e357b1f4d377a0891fbc85d34073cd30469b1..ad268dfd9e79f5540a4a85a9a439819fb3172640 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_dointvec_conv(const struct ctl_table *table, int dir, void *buffer,
+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_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_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);
-
-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));
+
+/*
+ * 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));
+
/*
* Register a set of sysctl names by calling register_sysctl
* with an initialised array of struct ctl_table's.
--
2.50.1
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