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Subject[PATCH v2 3/3] param: make /sys/module/*/paramaters optional
Date
From: David Decotigny <decot@google.com>

With this patch, we allow systems that don't want to pay the price for
/sys/module/*/paramaters to be compiled without that feature. This
abiltity can in turn encourage module developers to expose more of
their parameters with fewer hesitations (eg. memory concerns, etc.);
this is desirable to help debugging/auditing of live (larger) systems.
The new knob to control that is CONFIG_SYSFS_MODULE_PARAM available in
Kconfig in expert mode: File systems / Pseudo filesystems / sysfs file
system support / Module parameters in sysfs. It is enabled by default,
keeping /sys/module/*/paramaters/ available as before.
As an illustration, on my copy I see 1658 module_param() macros with
perm == 0: most of these could be exposed to user (perm != 0).

Tested:
- qemu + real x86_64 with defconfig customized:
CONFIG_EXPERT=y
CONFIG_SYSFS=y
# CONFIG_SYSFS_MODULE_PARAM is not set
- qemu + real x86_64 with defconfig
- make all with allyesconfig / allnoconfig / allmodconfig



Signed-off-by: David Decotigny <david.decotigny@google.com>
---
Documentation/ABI/stable/sysfs-module | 3 +++
Documentation/DocBook/kgdb.tmpl | 3 ++-
fs/sysfs/Kconfig | 15 ++++++++++++++-
include/linux/moduleparam.h | 4 ++--
kernel/params.c | 7 +++++++
5 files changed, 28 insertions(+), 4 deletions(-)
diff --git a/Documentation/ABI/stable/sysfs-module b/Documentation/ABI/stable/sysfs-module
index 75be431..a733ad8 100644
--- a/Documentation/ABI/stable/sysfs-module
+++ b/Documentation/ABI/stable/sysfs-module
@@ -15,6 +15,9 @@ Description:
documentation as to the contents of these parameters and
what they accomplish.

+ This directory is available only when
+ CONFIG_SYSFS_MODULE_PARAM is set (default).
+
Note: The individual parameter names and values are not
considered stable, only the fact that they will be
placed in this location within sysfs. See the
diff --git a/Documentation/DocBook/kgdb.tmpl b/Documentation/DocBook/kgdb.tmpl
index d71b57f..68a1d23 100644
--- a/Documentation/DocBook/kgdb.tmpl
+++ b/Documentation/DocBook/kgdb.tmpl
@@ -474,7 +474,8 @@
a kgdb I/O driver, kgdb will unregister all the kernel hook points.
</para>
<para> All kgdb I/O drivers can be reconfigured at run time, if
- <symbol>CONFIG_SYSFS</symbol> and <symbol>CONFIG_MODULES</symbol>
+ <symbol>CONFIG_SYSFS</symbol>, <symbol>CONFIG_MODULES</symbol> and
+ <symbol>CONFIG_SYSFS_MODULE_PARAM</symbol>
are enabled, by echo'ing a new config string to
<constant>/sys/module/&lt;driver&gt;/parameter/&lt;option&gt;</constant>.
The driver can be unconfigured by passing an empty string. You cannot
diff --git a/fs/sysfs/Kconfig b/fs/sysfs/Kconfig
index 8c41fea..22ac50c 100644
--- a/fs/sysfs/Kconfig
+++ b/fs/sysfs/Kconfig
@@ -1,4 +1,4 @@
-config SYSFS
+menuconfig SYSFS
bool "sysfs file system support" if EXPERT
default y
help
@@ -21,3 +21,16 @@ config SYSFS
example, "root=03:01" for /dev/hda1.

Designers of embedded systems may wish to say N here to conserve space.
+
+if SYSFS
+
+config SYSFS_MODULE_PARAM
+ bool "Module parameters in sysfs" if EXPERT
+ default y
+ help
+ Allow to enable/disable the availability of kernel module
+ parameters in /sys/module/[module_name]/parameters. When
+ unset, this will conserve some memory space. If unsure,
+ say Y.
+
+endif # SYSFS
diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 77d09f4..9c42200 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -213,7 +213,7 @@ __check_old_set_param(int (*oldset)(const char *, struct kernel_param *))
__kernel_param_unlock(); \
} while (0)

-#ifdef CONFIG_SYSFS
+#ifdef CONFIG_SYSFS_MODULE_PARAM
extern void __kernel_param_lock(void);
extern void __kernel_param_unlock(void);
#else
@@ -400,7 +400,7 @@ extern int param_get_string(char *buffer, const struct kernel_param *kp);

struct module;

-#if defined(CONFIG_SYSFS) && defined(CONFIG_MODULES)
+#if defined(CONFIG_SYSFS_MODULE_PARAM) && defined(CONFIG_MODULES)
extern int module_param_sysfs_setup(struct module *mod,
const struct kernel_param *kparam,
unsigned int num_params);
diff --git a/kernel/params.c b/kernel/params.c
index b0e1668..7b2137a 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -558,6 +558,9 @@ static struct module_kobject * __init locate_module_kobject(const char *name)

return mk;
}
+#endif /* CONFIG_SYSFS */
+
+#ifdef CONFIG_SYSFS_MODULE_PARAM

#define to_param_attr(n) container_of(n, struct param_attribute, mattr)

@@ -805,7 +808,9 @@ static void __init param_sysfs_builtin(void)
kernel_add_sysfs_param(modname, kp, name_len);
}
}
+#endif /* CONFIG_SYSFS_MODULE_PARAM */

+#ifdef CONFIG_SYSFS
ssize_t __modver_version_show(struct module_attribute *mattr,
struct module_kobject *mk, char *buf)
{
@@ -915,7 +920,9 @@ static int __init param_sysfs_init(void)
module_sysfs_initialized = 1;

version_sysfs_builtin();
+#ifdef CONFIG_SYSFS_MODULE_PARAM
param_sysfs_builtin();
+#endif /* CONFIG_SYSFS_MODULE_PARAM */

return 0;
}
--
1.7.3.1


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