January 2013 - 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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kernel driver vs userspace program
by Simon Feb. 12, 2013

Feb. 12, 2013

Hi guys, I'm building an electrical device which will be controlled by computer. It will have an embedded microcontroller and will use USB to communicate with the PC. I believe this calls automatically for a device driver, correct? And for using the machine from the PC, interacting with it, that calls for a userspace program, correct? I mean, doing things differently, such as all in userspace or all in-kernel, would be bad form, right? My question is in case the machine is used in an industrial context where there is really only one usage and one kind of interaction that follows a pre-determined procedure (therefore totally automated). This could give extremely high priority of execution, I guess. Similar to a factory robot controlled by a computer. Would it make more sense to have everything in kernel space, while the userspace (if any) would only serve the purpose of reporting? To be a lot more general, I find it simple at first glance to understand what goes where between kernel and user space. But despite this, I often find myself in a gray zone (to my perspective) or I find myself trying to "fit" something I feel is the wrong place. I would need to read more on the philosophy of these different processing spaces, about the design behind them and the usage this philosophy prescribes. Anyone know where I could read about this in greater detail? Thanks, Simon

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Any way to do time keeping during kernel uncompression[ARM architecture]
by sandeep kumar Feb. 7, 2013

Feb. 7, 2013

Hi All On ARM, Just for learning i am working on booting with uncompressed kernel. I am meddling with arch/arm/boot/compressed/head.S, and understand the relocation/decompression stuff through putting some logs. I want to check how much time it takes for kernel to relocate itself and how much time it takes to decompress etc., Is there any possibility of seeing the current time stamp here, like a register which keeps on counting immediately after boot.. With regards, Sandeep Kumar Anantapalli,

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thread concurrent file operation
by Karaoui mohamed lamine Feb. 7, 2013

Feb. 7, 2013

Hello, I was looking at how a syscall read/write was done, and i found this : .... loff_t pos = file_pos_read(f.file); ret = vfs_read(f.file, buf, count, &pos); file_pos_write(f.file, pos); fdput(f); ... My questions are : Where did the locking go? I would have imaginated something like : .... *lock(f);* loff_t pos = file_pos_read(f.file); ret = vfs_read(f.file, buf, count, &pos); file_pos_write(f.file, pos); fdput(f); *unlock(f);* ... If multiple threads try to read/write at the same time, they could read/write at the same offset ? If my understanding are correct, is this POSIX compliant ? thanks.

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Linux Kernel Networking document (free, 178 pages doc)
by Rami Rosen Feb. 4, 2013

Feb. 4, 2013

Hi everyone, You can find here an up to date and detailed document in pdf (178 pages) about Linux Kernel Networking; going deep into design and implementation details as well as the theory behind it: http://media.wix.com/ugd//295986_931b8bcf34d93419d46e05b5aa5d0216.pdf I believe that developers/sysadmins/researchers/students may find help with it. regards, Rami Rosen http://ramirose.wix.com/ramirosen

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How to make a bootable hard disk image?
by horseriver Feb. 4, 2013

Feb. 4, 2013

hi:) I want to boot kernel from hard disk image ,because i am using a virtual machine . How to make this bootable image ? After I make it ,how do I put kernel Image into this image? thanks!

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Kernel Config for Chromium Browser?
by Martin Kepplinger Feb. 4, 2013

Feb. 4, 2013

I stripped down my .config for my kernel-compilation a bit, but thought that I really just removed unnecessary stuff. But really, the consequency was, that the Chromium Browser didn't load _any_ page. Not even locally and no chrome:// page. It started, but just stayed at a white page. I didn't change the system whatsoever. I know it was the kernel. Does anyone by chance know what parameter caused that behaviour? What does chromium do differently? different than firefox. thanks

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