linux-kernel - Re: [PATCH 2/2] UBI: block: Implement kernel_param

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Date:	Wed, 19 Mar 2014 14:23:13 +0100
From:	Richard Weinberger <richard@....at>
To:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
CC:	dedekind1@...il.com, dwmw2@...radead.org,
	computersforpeace@...il.com, linux-mtd@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] UBI: block: Implement kernel_param_ops->get()

Am 19.03.2014 14:15, schrieb Ezequiel Garcia:
> Hi Richard,
> 
> On Mar 19, Richard Weinberger wrote:
>> The ->get() function is not optional.
>>
> 
> [..]
>>  static struct kernel_param_ops ubiblock_param_ops = {
>>  	.set    = ubiblock_set_param,
>> +	.get	= param_get_charp,
>>  };
>>  module_param_cb(block, &ubiblock_param_ops, NULL, 0);
> 
> The comment for the function says they are both optional:
> 
> /**
>  * module_param_cb - general callback for a module/cmdline parameter
>  * @name: a valid C identifier which is the parameter name.
>  * @ops: the set & get operations for this parameter.
>  * @perm: visibility in sysfs.
>  *
>  * The ops can have NULL set or get functions.
>  */
> 
> This has no visibility in sysfs, so I can't see how having a NULL
> get() is a problem. What's the issue you're trying to fix here?
> 
> Maybe I'm missing something?
> 

Maybe I've misread the struct.

struct kernel_param_ops {
        /* How the ops should behave */
        unsigned int flags;
        /* Returns 0, or -errno.  arg is in kp->arg. */
        int (*set)(const char *val, const struct kernel_param *kp);
        /* Returns length written or -errno.  Buffer is 4k (ie. be short!) */
        int (*get)(char *buffer, const struct kernel_param *kp);
        /* Optional function to free kp->arg when module unloaded. */
        void (*free)(void *arg);
};

To me it looks like only ->free is optional.

Thanks,
//richard
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