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sysctl: Group proc_handler declarations and document

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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>
This commit is contained in:
Joel Granados 2026-06-25 22:38:19 +02:00
parent b96b5c6708
commit 75fe29b9aa
1 changed files with 88 additions and 42 deletions
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130
include/linux/sysctl.h
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@ -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);
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,
typedef int proc_handler(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,
/* 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_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.