December 2012 - kernelnewbies@kernelnewbies.org

How to get the inode - no path_lookup
by Rishi Agrawal Sept. 17, 2015

Sept. 17, 2015

Hi All, I had a module which used the path_lookup function to print the details of any file's inode. I now want to rewrite that module in order to show some juniors how to write some code in kernel. I am using 3.4.6 kernel, I tried finding out path_lookup but google showed that it has been removed. I tried the following code then which did not work . . . dentry = kern_path_create(AT_FDCWD, filename, &path, 1); if (IS_ERR(dentry)) { printk("Failed to obtain the dentry"); return; } its not returning dentry I again tried after seeing the implementation of vfs_stat function user_path_at(AT_FDCWD, filename, lookup_flags, &path); but this also fails. I am using a proc interface to pass the filename, and copying the filename into a kernel buffer. How can I get a copy of vfs inode for a file name. -- Regards, Rishi Agrawal

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How kernel handle interrupts
by Woody Wu Aug. 5, 2013

Aug. 5, 2013

Hi, List Where is the Kernel code that handles external interrupts? I want to have a look at it but haven't found out where it is. Actually, I have some basic questions about interrupt handling in Linux. 1. After Kernel's ISR received an interrupt, I believe it will invoke a handler defined in a device driver if any. But it should be the device driver's responsibility or kernel ISR's responsibility to clear (or acknowledge) the interrupt? 2. My device, an AX88796B network controller, asserting the interrupt line in a level-triggered manner. Now I met problem with the device that might caused by the CPU interrupt mode is not set as level-triggered by edge trigger. My CPU is Samsung S3C2410, an ARM920T powered one. Does anyone know usually where and how should I do this kind of setting? Thanks in advance. -- woody I can't go back to yesterday - because I was a different person then.

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linux segment
by Fan Yang June 20, 2013

June 20, 2013

Hi all: I print the cs ds and ss register in the user space, and it is same as the __USER_CS and __USER_DS which defined in kernel as 73 and 7b. In the kernel __KERNEL_CS and __KERNEL_DS defined as 60 and 68, but when I print this two value in my kernel module, I get 60 and 7b. Why ? It should be 60 and 68, shouldn't it?

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Queries on USB skeleton Driver
by sanchayan maity Feb. 22, 2013

Feb. 22, 2013

Hello, I wanted to use the usb-skeleton driver for transferring data to a pen drive. I am using Ubuntu 12.04 with kernel version 3.2.0. I remove the usb-storage driver with rmmod and then inserted the skeleton module. The module is inserted successfully. On inserting the drive, usb-storage module gets automatically loaded. To avoid this, i tried blacklisting the module by including a blacklist entry in blacklist.conf and rebooting. This didn't work either and usb-storage gets automatically loaded again. Can someone point out how i can use the usb-skeleton driver and also test it. I also have Arch linux set up, but, i have not tried the above on it yet. Thanks & Regards, Sanchayan.

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Block device driver: how to terminate the block device if media disappears?
by John Beard Jan. 12, 2013

Jan. 12, 2013

Hi, I have block driver for a hot-pluggable device PCIe storage device on kernel version 2.6.43 (which I know isn't a mainline kernel version, but it's what I am required to build against). The driver itself is relatively simple and implements the following block operations: static struct block_device_operations mydev_ops = { .owner = THIS_MODULE, .open = mydev_open, .release = mydev_release, .getgeo = mydev_getgeo, .ioctl = mydev_ioctl }; and the following PCI driver structure: static struct pci_driver mydev_driver = { .name = DRIVER_NAME, .probe = mydev_pci_init_one, .remove = mydev_pci_remove_one, .id_table = mydev_pci_tbl, }; As well as a request_fn with the following signature: static void mydev_submit_req(struct request_queue *q); Whenever I get IO requests, there is the expected pattern of "open, IO, release", and everything works OK. However, if the device is physically removed during IO, I never seem to get a "release", just "open, IO, hang". I believe (but I don't know), that this is preventing del_gendisk() from completing, thus hanging the cleanup of the driver, which is triggered by mydev_pci_remove_one() upon the removal of the device. I am ending all requests on the queue once an eject happens, but it still doesn't seem to cause a release. What is the right way to terminate requests and delete the gendisk in the case of physically vanished PCI devices (or even devices in general)? Thanks in advance for any pointers to a solution and apologies to the IRC folks for annoying them with the same question! John Beard

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calling system call in arm from user space
by Niroj Pokhrel Jan. 9, 2013

Jan. 9, 2013

Hi, I have written a system call and build it with kernel for Arm architecture. However, I'm confused to use it to call it from the user space. As it is in x86, where we can simply call by using sycall() function and the return value is returned by the syscal() itself. In Arm, I tried to write an assembly language program and was able to call the system call using the assembly code but what I'm confused is how to call this function using C program. I tried using inline assembly but it didn't work. Further, if I can implement it using inline assembly then return value will be in r0 and how can I move this value to the user variable. Thanking you in advance. -- Niroj Pokhrel Software Engineer, Samsung India Software Operations

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Locating the keyboard driver (and replacing it)
by manty kuma Jan. 8, 2013

Jan. 8, 2013

Hi, I have written a small module that toggles the capslock LED. To demonstrate it i want to replace the Existing keyboard module with mine. I tried lsmod|grep "key" without any success. also checked /proc/modules. I couldnot find any clue regarding the name of the module i need to uninstall. So, How can i remove the existing keyboard module and insert mine? Regards, Manty

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trace_console function definition not found in Linux kernel v3.5
by siddharth goel Jan. 2, 2013

Jan. 2, 2013

In file *kernel/printk.c *in Linux Kernel *3.5 *there is a function call *trace_console(text, 0, len, len); *@line 1219 . But I could not find the definition for same. Am I missing any concept ? -- Thanks and Regards, Siddharth Goel

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sys fs interface
by Rahul Bedarkar Dec. 31, 2012

Dec. 31, 2012

Hi, When driver provides sys fs interface for user space programs, how we specify name of file to be created ? Thanks, Rahul B.

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Re: how to look for source code in kernel
by Jonathan Neuschäfer Dec. 28, 2012

Dec. 28, 2012

On Fri, Dec 28, 2012 at 11:49:53AM -0800, Eric W. Biederman wrote: > Al Viro <viro(a)ZenIV.linux.org.uk> writes: > > > On Thu, Dec 27, 2012 at 11:36:13PM -0800, Eric W. Biederman wrote: > >> But then I am probably peculiar keeping an index of the source code in > >> my head. When I need to look for something and I don't know where to > >> find it I do. > >> > >> git-ls-files | xargs fgrep 'struct f2fs_inode' > > > > What's wrong with git grep? > > I haven't learned it yet. git-ls-files is a lot better than find > speed wise so is very much worth doing. I haven't a clue if > there is an advantage to git-grep, over just knowing find, xargs, and > grep. Brevity. Jonathan

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