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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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