December 2012 - kernelnewbies@kernelnewbies.org

Query on vfs interface
by Raghavendra G Dec. 21, 2012

Dec. 21, 2012

Hello I am trying to log all the calls going to the VFS file system from the application. For write calls I notice an anomaly. I introduced a log at the vfs_write() function , I see it get's logged twice for every write in the log output. I also tried do_sync_write() the result is same. Time stamp VFS Action filename Size time taken(us) 626.212738 OPEN /data/media/DCIM/Camera/VID_20000101_002412.mp4.tmp flags=131585 mode =0 628.187652 WRITE VID_20000101_002412.mp4.tmp 101606 611 628.187713 WRITE VID_20000101_002412.mp4.tmp 101606 1160 628.188995 WRITE VID_20000101_002412.mp4.tmp 69782 457 628.189056 WRITE VID_20000101_002412.mp4.tmp 69782 885 Any clue why this anomaly ? Warm Regards Raghavendra G

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Re: Need of MODULE_LICENSE("GPL")
by Niroj Pokhrel Dec. 20, 2012

Dec. 20, 2012

On Thu, Dec 20, 2012 at 4:00 PM, Ivan Nikolaev <voidexp(a)gmail.com> wrote: > Modules which are not declared.as GPL, by default are considered > proprietary. Proprietary code can't make use of GPLed modules. > 20.12.2012 12:03 пользователь "Niroj Pokhrel" <nirojpokhrel(a)gmail.com> > написал: > >> Hi, >> While writing a device driver, I noticed MODULE_LICENSE("GPL"). When I >> omitted it, I got several error like device_create, device_destroy, >> class_create, class_destroy is not recognized symbol. I am just wondering >> what is the use of this macro and how does it helps in defining the >> symbols. Thanks in advance. >> >> -- >> Niroj Pokhrel >> Software Engineer, >> Samsung India Software Operations >> >> _______________________________________________ >> Kernelnewbies mailing list >> Kernelnewbies(a)kernelnewbies.org >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> >> Thank you Ivan. But can you please give me some insight on proprietary code and GPLed modules. Thanking you in advance. -- Niroj Pokhrel Software Engineer, Samsung India Software Operations

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Need of MODULE_LICENSE("GPL")
by Niroj Pokhrel Dec. 20, 2012

Dec. 20, 2012

Hi, While writing a device driver, I noticed MODULE_LICENSE("GPL"). When I omitted it, I got several error like device_create, device_destroy, class_create, class_destroy is not recognized symbol. I am just wondering what is the use of this macro and how does it helps in defining the symbols. Thanks in advance. -- Niroj Pokhrel Software Engineer, Samsung India Software Operations

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How to choice the Open source project about kernel?
by lx Dec. 20, 2012

Dec. 20, 2012

hi: How to choice the Open source project about kernel? I'm a new one, and I want to practice the technology about kernel. Please list some simple projects, thank you

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sysfs: pass function pointers to kernel (not just a value through attribute)
by Terry Hsu Dec. 19, 2012

Dec. 19, 2012

Hello everyone, I am looking for some mechanism for userspace tasks to pass certain functions to kernel and let the kernel execute these functions on behalf of userspace tasks. I know that sysfs can be used with kobject embedded into internal kernel structure to access kernel variables. But is there anyway for userspace tasks to pass a function to kernel to execute through sysfs? PS: adding syscall in the kernel can certainly satisfy my needs but it is less favorable because the new kernel service I want to add is not that general to be added as a new syscall. Thanks in advance! T

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misc device question
by Kevin Wilson Dec. 19, 2012

Dec. 19, 2012

Hello,kernelnewbies I am trying to develop a misc driver in 3.7.0 kernel. As a basis I copy and paste this code, *without any change*, http://virtlog.com/2008/03/25/linux-miscdevice-sample/ And build it. after insmod I have : [root@n miscDevice]\>ls -al /dev/mymisc crw------- 1 root root 10, 59 Dec 19 10:24 /dev/mymisc However, when trying to open this file I get: open: No such file or directory Any ideas why ? The program with which I try to open the device is simple, a few lines following here: int main() { int fd; fd = open("/dev/mymodule", O_RDONLY); if (fd == -1) { perror("open"); exit(1); } printf("open succeeded\n"); } Any ideas why this error ? rgs, Kevin

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Question regarding patches
by Shraddha Kamat Dec. 19, 2012

Dec. 19, 2012

Sorry if this is not relevant to kernel. But since I am patching the kernel - Please consider this as a uber beginner question to ask on this mailing list - forgive me for that. Now my question is - What "@@ -321,7 +321,8 @@" mean in this snippet from the patch - diff --git a/exec.h b/exec.h index 722c620..6abb687 100644 --- a/exec.h +++ b/exec.h @@ -321,7 +321,8 @@ static void acct_arg_size(struct linux_binprm *bprm, unsigned long pages); -- Shraddha

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Opening a device driver file.
by Niroj Pokhrel Dec. 18, 2012

Dec. 18, 2012

Hi, I have been trying to open a device driver after inserting it in the kernel from the userspace. Everything seems to be fine, the class is created and is also exported to the device directory but there seems to be some problem as every time I try to open it, the open process fails. My code is below, Please help. Thanx in advance. #include<linux/init.h> #include<linux/device.h> #include<linux/fs.h> #include<asm-generic/uaccess.h> #include<linux/module.h> #include<linux/kernel.h> #include<linux/cdev.h> #include<linux/string.h> MODULE_LICENSE("Dual BSD/GPL"); #define DEVICE_NAME "niroj_char" static const int success=0; static struct cdev *mydevice; struct class *myclass; static char Buffer[]="My Name is Niroj"; static ssize_t device_read(struct file *,char *,size_t,loff_t*); static ssize_t device_write(struct file *,const char *,size_t,loff_t*); static int device_open(struct inode *,struct file *); static int device_release(struct inode *,struct file *); static struct device *my_device; static struct file_operations fops= { .read = device_read, .write = device_write, .open = device_open, .release = device_release, }; static int hello_init(void) { int rvalue; int errorcode; rvalue=success; mydevice=cdev_alloc(); errorcode=alloc_chrdev_region(&(mydevice->dev),0,1,DEVICE_NAME); if(!errorcode) { printk(KERN_ALERT "\nSuccessfully done so far now we have to create node and other things."); mydevice->ops=&fops; mydevice->owner=THIS_MODULE; cdev_add(mydevice,mydevice->dev,1); myclass=class_create(THIS_MODULE,DEVICE_NAME); my_device=device_create(myclass,NULL,mydevice->dev,NULL,DEVICE_NAME); if(my_device==NULL) printk(KERN_ALERT "Device Node hasn't been created successfully."); } else { rvalue=errorcode; printk(KERN_ALERT "\nUnsuccessful allocation of chrdev"); } printk(KERN_ALERT "Bye Bye Init"); return 0; } static void hello_exit(void) { printk(KERN_ALERT "Enter the exit function"); device_destroy(myclass,mydevice->dev); class_destroy(myclass); unregister_chrdev_region(mydevice->dev,1); cdev_del(mydevice); printk(KERN_ALERT "Exit the exit function"); } static int device_open(struct inode *inode, struct file *filp) { printk(KERN_ALERT "device opened successfully."); return success; } static int device_release(struct inode *inode,struct file *filp) { printk(KERN_ALERT "device released successfully."); return success; } static ssize_t device_read(struct file *file,char *buffer,size_t lenght,loff_t *offset) { ssize_t totalbytes; ssize_t bytesnotcopied; totalbytes=strlen(Buffer); bytesnotcopied=copy_to_user(buffer,Buffer,totalbytes); return (ssize_t)(totalbytes-bytesnotcopied); } static ssize_t device_write(struct file *file,const char *buffer,size_t length,loff_t *offset) { size_t bytesnotcopied; bytesnotcopied=copy_from_user(Buffer,buffer,length); printk(KERN_ALERT "%s",Buffer); return (ssize_t)(length-bytesnotcopied); } module_init(hello_init); module_exit(hello_exit); Similarly, my user space program is as follows : #include<stdio.h> #include<string.h> #include<fcntl.h> #define DEVICE_PATH "/dev/niroj_char" static char Buffer[256]; int main() { int fd; if((fd=open(DEVICE_PATH,O_RDWR,0x777))<=0) printf("\nDevice Open Failed %d ",fd); if(read(fd,Buffer,sizeof(Buffer))==0) printf("\nThe data hasn't been read"); else printf("\n The copied string is %s ",Buffer); strcpy(Buffer,"Niroj you are a dude"); if(write(fd,Buffer,sizeof(Buffer))==0) printf("\nThe data hasn't been written"); return 0; } Output: Device Open Failed -1 -- Niroj Pokhrel Software Engineer, Samsung India Software Operations

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how does this command(at+cfun=1,1) works?
by Ritesh Harjani Dec. 17, 2012

Dec. 17, 2012

Hi Everyone, When this command (at+cfun=1,1) is executed on phone, it does a reboot. I want to know which and how this command calls the kernel level functions. I googled this, but seems like all the data explains only about AT command and not as to how this reboot process is done. Coz what I know is that reboot process needs a syncing of filesystem, so this command must be calling some kernel functions to do that. Please if anyone can give more detail on this. Thank you Ritesh

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8250 serial device named "ttsN" ?
by Woody Wu Dec. 17, 2012

Dec. 17, 2012

Hi, Does anyone remember, in what kernel version, the 8250/16550 serial devices are named after ttsN, i.e., tts0, tts1, tts2? Thanks in adavnce. -- woody I can't go back to yesterday - because I was a different person then.

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