linux-kernel - Re: [PATCH] Show version information for built-in modules in sysfs

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Message-Id: <201012221218.45533.rusty@rustcorp.com.au>
Date:	Wed, 22 Dec 2010 12:18:45 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Dmitry Torokhov <dtor@...are.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Show version information for built-in modules in sysfs

On Wed, 22 Dec 2010 11:47:12 am Dmitry Torokhov wrote:
> On Tue, Dec 21, 2010 at 05:02:40PM -0800, Rusty Russell wrote:
> > On Thu, 16 Dec 2010 08:30:19 am Dmitry Torokhov wrote:
> > > Currently only drivers that are built as modules have their versions
> > > shown in /sys/module/<module_name>/version, but this information might
> > > also be useful for built-in drivers as well. This especially important
> > > for drivers that do not define any parameters - such drivers, if
> > > built-in, are completely invisible from userspace.
> > > 
> > > This patch changes MODULE_VERSION() macro so that in case when we are
> > > compiling built-in module, version information is stored in a separate
> > > section. Kernel then uses this data to create 'version' sysfs attribute
> > > in the same fashion it creates attributes for module parameters.
> > > 
> > > Signed-off-by: Dmitry Torokhov <dtor@...are.com>
> > > ---
> > > 
> > > This change is driven by our desire to detect whether vmw_balloon driver
> > > is built-in into the kernel when we installing our tool package in the
> > > guest and avoid installing our own version of the driver.
> > > 
> > > Since vmw_balloon does not have any module parameter nor registers any
> > > driver core devices, without this patch it is completely invisible from
> > > userspace when built into the kernel.
> > > 
> > > Thanks,
> > > Dmitry
> > > 
> > >  include/asm-generic/vmlinux.lds.h |    7 ++++
> > >  include/linux/module.h            |   27 +++++++++++++++
> > >  kernel/params.c                   |   65 ++++++++++++++++++++++++++++++------
> > >  3 files changed, 88 insertions(+), 11 deletions(-)
> > > 
> > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> > > index bd69d79..0d83dd1 100644
> > > --- a/include/asm-generic/vmlinux.lds.h
> > > +++ b/include/asm-generic/vmlinux.lds.h
> > > @@ -355,6 +355,13 @@
> > >  		VMLINUX_SYMBOL(__start___param) = .;			\
> > >  		*(__param)						\
> > >  		VMLINUX_SYMBOL(__stop___param) = .;			\
> > > +	}								\
> > > +									\
> > > +	/* Built-in module versions. */					\
> > > +	__modver : AT(ADDR(__modver) - LOAD_OFFSET) {			\
> > > +		VMLINUX_SYMBOL(__start___modver) = .;			\
> > > +		*(__modver)						\
> > > +		VMLINUX_SYMBOL(__stop___modver) = .;			\
> > >  		. = ALIGN((align));					\
> > >  		VMLINUX_SYMBOL(__end_rodata) = .;			\
> > >  	}								\
> > > diff --git a/include/linux/module.h b/include/linux/module.h
> > > index 7575bbb..f74ddda 100644
> > > --- a/include/linux/module.h
> > > +++ b/include/linux/module.h
> > > @@ -58,6 +58,12 @@ struct module_attribute {
> > >  	void (*free)(struct module *);
> > >  };
> > >  
> > > +struct module_version_attribute {
> > > +	struct module_attribute mattr;
> > > +	const char *module_name;
> > > +	const char *version;
> > > +};
> > > +
> > >  struct module_kobject
> > >  {
> > >  	struct kobject kobj;
> > > @@ -161,7 +167,28 @@ extern struct module __this_module;
> > >    Using this automatically adds a checksum of the .c files and the
> > >    local headers in "srcversion".
> > >  */
> > > +
> > > +#ifdef MODULE
> > >  #define MODULE_VERSION(_version) MODULE_INFO(version, _version)
> > > +#else
> > > +#define MODULE_VERSION(_version)					\
> > > +	extern ssize_t __modver_version_show(struct module_attribute *,	\
> > > +					     struct module *, char *);	\
> > > +	static struct module_version_attribute __modver_version_attr	\
> > > +	__used								\
> > > +    __attribute__ ((unused,__section__ ("__modver"),aligned(sizeof(void *)))) \
> > 
> > __used and unused seems overkill, and confused.
> > 
> 
> Must admit that I copied used/unused verbatim from linux/moduleparam.h:
> 
> /* This is the fundamental function for registering boot/module
>    parameters. */
> #define __module_param_call(prefix, name, ops, arg, isbool, perm)	\
> 	/* Default value instead of permissions? */			\
> 	static int __param_perm_check_##name __attribute__((unused)) =	\
> 	BUILD_BUG_ON_ZERO((perm) < 0 || (perm) > 0777 || ((perm) & 2))	\
> 	+ BUILD_BUG_ON_ZERO(sizeof(""prefix) > MAX_PARAM_PREFIX_LEN);	\
> 	static const char __param_str_##name[] = prefix #name;		\
> 	static struct kernel_param __moduleparam_const __param_##name	\
> 	__used								\
>     __attribute__ ((unused,__section__ ("__param"),aligned(sizeof(void *)))) \
> 	= { __param_str_##name, ops, perm, isbool ? KPARAM_ISBOOL : 0,	\
> 	    { arg } }
> 
> 
> So should it be removed from here as well?

I think so, but (as always!) check git blame.

Patch welcome!
Rusty.
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