Sysfs class attribute problem
Pranay Kumar Srivastava
Pranay.Shrivastava at hcl.com
Thu Jun 21 04:23:36 EDT 2012
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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 <jharan at bytemobile.com>
> Subject: RE: A confusion about invoking my syscall
> To: ?? <wangzhe5004 at gmail.com>
> Cc: kernelnewbies <kernelnewbies at kernelnewbies.org>
> Message-ID:
> <4AB110E2FA959F41AC8480E84516371105B80D at HQ-EX01.bytemobile.com>
> 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 at bytemobile.com>>
>
>
> From: ?? [mailto:wangzhe5004 at gmail.com<mailto:wangzhe5004 at gmail.com>]
> 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 at 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 <jeshkumar555 at gmail.com>
> Subject: Re: Sysfs class attribute problem
> To: anish singh <anish198519851985 at gmail.com>
> 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
> <anish198519851985 at gmail.com>wrote:
>
> > On Tue, Jun 19, 2012 at 3:14 PM, jeshwanth Kumar N K
> > <jeshkumar555 at gmail.com> 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
> > >
> > >
> > >
> > >
> > > _______________________________________________
> > > Kernelnewbies mailing list
> > > Kernelnewbies at kernelnewbies.org
> > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
> > >
> >
>
>
>
> --
> Regards
> Jeshwanth Kumar N K
> +91-7411483498
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