Sysfs class attribute problem

all subsystems

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Today's Topics:

   1. RE: A confusion about invoking my syscall (Jeff Haran)
   2. Re: Sysfs class attribute problem (Jeshwanth Kumar N K Jeshu)

----------------------------------------------------------------------

Message: 1
Date: Wed, 20 Jun 2012 16:58:30 +0000
From: Jeff Haran <redacted>
Subject: RE: A confusion about invoking my syscall
To: ?? <redacted>
Cc: kernelnewbies <redacted>
Message-ID:
	[ref]
Content-Type: text/plain; charset="iso-2022-jp"

From: ?? [mailto:wangzhe5004 at gmail.com]
Sent: Wednesday, June 20, 2012 1:16 AM
To: Jeff Haran
Cc: kernelnewbies
Subject: Re: A confusion about invoking my syscall

2012/6/20 Jeff Haran
<jharan at bytemobile.com<mailto:jharan@bytemobile.com>>

From: ?? [mailto:wangzhe5004 at gmail.com<mailto:<redacted>>]
Sent: Monday, June 18, 2012 9:32 PM
To: Jeff Haran
Cc: kernelnewbies
Subject: Re: A confusion about invoking my syscall

2012/6/19 Jeff Haran
<jharan at bytemobile.com<mailto:jharan@bytemobile.com>>

From: kernelnewbies-bounces at kernelnewbies.org<mailto:kernelnewbies-
bounces at kernelnewbies.org> [mailto:kernelnewbies-
bounces at kernelnewbies.org<mailto:kernelnewbies-
bounces at kernelnewbies.org>] On Behalf Of ??
Sent: Monday, June 18, 2012 6:40 PM
To: kernelnewbies
Subject: A confusion about invoking my syscall

Hello everyone:

         I append a simple syscall in kernel. and the function is as
follows:

  asmlinkage  long sys_mysyscall(long data)
 {
          printk("This is my syscall!\n");
          return data;
  }

and i test it sucessfully in user space . and the test program:

   #include <linux/unistd.h>
   #include <syscall.h>
   #include <sys/types.h>
   #include <stdio.h>

   int main(void)
   {
   long n = 0,m = 0,pid1,pid2;
   n = syscall(345,190);// #define __NR_mysyscall          345
   printf("n = %ld\n",n);
   pid1 = syscall(SYS_getpid);  //getpid
   printf("pid = %ld\n",pid1);
   pid2 = syscall(20);  //getpid
   printf("pid = %ld\n",pid2);
   return 0;
  }
and the result:
n = 190
pid = 4097
pid = 4097

but if the test program is:
#include <linux/unistd.h>
#include <syscall.h>
#include <sys/types.h>
#include <stdio.h>

int main(void)
{
 long n = 0,m = 0,pid1,pid2;
 n = syscall(345,190);// #define __NR_mysyscall          345
 printf("n = %ld\n",n);
 m = syscall(SYS_mysyscall,190);
 printf("m = %ld\n",m);
 pid1 = syscall(SYS_getpid);  //getpid
 printf("pid = %ld\n",pid1);
 pid2 = syscall(20);  //getpid
 printf("pid = %ld\n",pid2);
 return 0;
}
and the result:
wanny at wanny-C-Notebook-XXXX:~/syscall/src$ gcc test1.c
test1.c: In function ?main?:
test1.c:13:14: error: ?SYS_mysyscall? undeclared (first use in this
function)
test1.c:13:14: note: each undeclared identifier is reported only once
for each function it appears in

why i can't invoke my syscall with "SYS_mysyscall"?

Thanks in advance!
Because it appears you never defined the symbol SYS_mysyscall.
 I think so,but where shoud i defne the  symbol SYS_mysyscall ?
  and where is the symbol SYS_getpid defined?
On my system /usr/include/bits/syscall.h, which is being included in
your program because it includes syscall.h.
           83 #define SYS_getpid __NR_getpid  ?so SYS_getpid is
replaced by __NR_getpid. and __NR_getpid was defined in the
kernel(arch/x86/include/asm/unistd_32.h). and my syscall was also
defined there.#define SYS_mysyscall __NR_mysyscall, i don't kown why it
doesn't works.

My sources contain no reference to SYS_mysyscall nor __NR_mysyscall, so
I assume you?ve added them to the Linux include files that you built
your module from.

User space programs like your main() program above generally aren?t
going to include Linux source tree include files. When you include
<syscall.h> from a user space program in a typical development
environment, the compiler is by default going to look for syscall.h in
/usr/include, not in the Linux source tree where presumably you?ve made
your modifications. Of course you can always tell the compiler to look
there using the -I command line option to gcc, if you want to. The
usual practice however is to keep kernel code and user code include
files completely separate. That means some duplication of effort, like
having to define SYS_mysyscall in two different places, but that?s the
usual practice because most people aren?t building kernels and thus
haven?t installed the kernel source include files.

Jeff Haran

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Message: 2
Date: Wed, 20 Jun 2012 23:32:12 +0530
From: Jeshwanth Kumar N K Jeshu <redacted>
Subject: Re: Sysfs class attribute problem
To: anish singh <redacted>
Cc: kernelnewbies at kernelnewbies.org
Message-ID:
	<CAC-LjFsrQk4FQab-Yb=ZKExd_FT9dB0X_BvLK6R-
oGuOpVXtPg at mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"

Hello

Thank you anish for the reply, the code is I pasted below.
[code-starts]

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <linux/sysdev.h>
#include <linux/major.h>
#include <asm/uaccess.h>
#include <linux/slab.h>
#include <linux/cdev.h>
#include <linux/kdev_t.h>

static char *gvar = "BeHonest";
Your gvar doesn't point to any allocated or statically allocated memory.....

// Store and Show functions......
 static ssize_t attr1_store(struct class *cls, struct class_attribute
*attr, const char *buf, size_t count);
 static ssize_t attr1_show(struct class *cls, struct class_attribute
*attr,
char *buf);

static struct class_attribute pwm_class_attrs[] = {
    __ATTR(attr1, S_IRUGO | S_IWUSR , attr1_show, attr1_store),
    __ATTR_NULL
};

static struct class pwm_class =
{
    .name = "dev_jes",
    .owner = THIS_MODULE,
    .class_attrs = pwm_class_attrs
};

static int hello_init(void)
{
    class_register(&pwm_class);
    printk("In hello_init function \n");

    return 0;
}

static ssize_t attr1_show(struct class *cls, struct class_attribute
*attr,
char *buf)
{

    printk("In attr1_show function\n");
    return sprintf(buf, "%s\n", gvar);
}

static ssize_t attr1_store(struct class *cls, struct class_attribute
*attr,
const char *buf, size_t count)
{
            printk("the string is : %s\n",buf);
            printk("In attr1_store function\n");
            return 1;
            //return sprintf(gvar, "%s\n", buf);  --- If I put this
line I
am getting ERROR :(
Ofcourse you'll....! gvar isn't allocated memory... you are trying to over write a read only memory area.
}

static void  hello_exit(void)
{
    class_unregister(&pwm_class);
    printk("In hello_exit function \n");
}

module_init(hello_init);
module_exit(hello_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Jeshwanth");
MODULE_DESCRIPTION("Learning sysfs");

[code-ends]

echo "jeshu" > /sys/class/dev_jes/attr1

And If I pass the command to atttribute I got result below in dmesg.

[ 3435.613057] the string is : jeshu
[ 3435.613061]
[ 3435.613066] In attr1_store function
[ 3435.613072] the string is : eshu
[ 3435.613074]
[ 3435.613078] In attr1_store function
[ 3435.613083] the string is : shu
[ 3435.613085]
[ 3435.613088] In attr1_store function
[ 3435.613093] the string is : hu
[ 3435.613095]
[ 3435.613098] In attr1_store function
[ 3435.613103] the string is : u
[ 3435.613105]
[ 3435.613108] In attr1_store function
[ 3435.613113] the string is :
[ 3435.613115]
[ 3435.613118] In attr1_store function

So please help me how to read the attribute in store function.. Thanks
:)

On Tue, Jun 19, 2012 at 4:02 PM, anish singh
[off-list ref]wrote:

On Tue, Jun 19, 2012 at 3:14 PM, jeshwanth Kumar N K
[off-list ref] wrote:
Hello all

I am new to sysfs interface ans I read about in mochel's
documentation.
And
doing some experiements on it. Let's come to Tue problem, in my
module I
have a global variable type char* myglobal and it s static, I am
putting
that value in my one and only class attribute using show function.
But
for
the same if I a user put some value in to the using echo or
something,
the
attribute value is not changing. And one more thing s after I
passed the
value to the attribute my system not shutting down :( . Please help
me
how
to read values.
Why don't you post your code?As that will really help and moreover as
this is your code
you won't be breakign any law set by your company.
// in store function I am doing this:
Myglobal = bus;

Sent from my HTC

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--
Regards
Jeshwanth Kumar N K
+91-7411483498
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