More info about kobj_attribute store and show functions

[Jeff Haran]

From: kernelnewbies-bounces+jharan=bytemobile.com at kernelnewbies.org [mailto:kernelnewbies-bounces+jharan=bytemobile.com at kernelnewbies.org] On Behalf Of Lucas Tanure
Sent: Wednesday, September 03, 2014 5:11 PM
To: kernelnewbies
Subject: Re: More info about kobj_attribute store and show functions

(Forget the last e-mail, please, stupid Gmail)

Hi,

I'm looking for some information about :

struct kobj_attribute {
        struct attribute attr;
        ssize_t (*show)(struct kobject *kobj, struct kobj_attribute *attr, char *buf);
        ssize_t (*store)(struct kobject *kobj, struct kobj_attribute *attr, const char *buf, size_t count);
};


My function to handle the operation:

static ssize_t my_store(struct kobject *kobj, struct kobj_attribute *attr, const char *buf, size_t count) {
char *buffer;

        buffer = (char*) kcalloc(count, sizeof(char), GFP_KERNEL);

        copy_from_user(buffer, buf, count);
        .....
        .....
        etc....
}

So, this const char *buf, where ti come from ? Kernel space?
My copy_from_user it's not working. Should return zero.

There any Macro or function to test if the pointer buf is a kernel pointer ?

Thanks

Lucas Tanure

I haven’t written too many of these things, but the last time I wrote a store function I didn’t need to do the copy_to_user().
buf seemed to point to directly accessible kernel memory. I would think a simple memcpy above would do the trick.

Jeff

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