February 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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64bit MMIO access
by Jagath Weerasinghe March 11, 2013

March 11, 2013

Hi, What are the read/write kernel functions to access 64bit MMIO addresses? Are there similar functions like readl() and writel() for 64bit systems? Regards, Jagath

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How to measure the RAM read/write performance
by sandeep kumar March 4, 2013

March 4, 2013

Hi All In performance benchmark tools, When we profile read/write timings mostly, those read/writes are done to cache only. I want to measure my DDR(RAM chip) performance. So i want to make sure, every read/write should happen to DDR RAM chip only. How can i achieve this...Any ideas/suggestions...? -- With regards, Sandeep Kumar Anantapalli,

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relocatable modules' symbols
by horseriver March 1, 2013

March 1, 2013

hi: I have built vmlinux at the top dir of kernel source ,then I use objdump to look into its section information.I find the statup_32 which is the start routine of kernel , locats at 0xc0100000. I know the 0x100000 is the defined address for locating protect-mode code .But which I can not understand is the 0xc prefix .where does it come from? thanks!

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Examples of Per-CPU Variables in Kernel source
by Shraddha Kamat March 1, 2013

March 1, 2013

I was reading about Per-CPU Variables from UTLK. Where are such variables used in the kernel source code - example. -- Shraddha

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atomic operations
by Shraddha Kamat March 1, 2013

March 1, 2013

what is the relation between atomic operations and memory alignment ? I read from UTLK that "an unaligned memory access is not atomic" please explain me , I am not able to get the relationship between memory alignment and atomicity of the operation.

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64bit MMIO access
by Jagath Weerasinghe Feb. 28, 2013

Feb. 28, 2013

Hi, What are the read/write kernel functions to access 64bit MMIO addresses? Are there similar functions like readl() and writel() for 64bit systems? Regards, Jagath

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doesn't ioremap() retrun contigious addressess...?
by sandeep kumar Feb. 28, 2013

Feb. 28, 2013

Hi All Please find a piece of code that i wrote in my driver, void __iomem *tcpm_base = ioremap_nocache(0x03900000, SZ_16KB); printk("Virtual addresss %x\n",tcpm_base); if(tcpm_base!=NULL) { printk("Jiffies %x %ld\n\n\n\n", jiffies, jiffies); for(i=0;i<(SZ_16KB-1);i++) src = readl(tcpm_base+i); printk("%d\n",src); printk("Jiffies %x %ld\n\n\n\n", jiffies, jiffies); } else printk("unable to map \n"); When i execute this code, i am seeing a kernel panic telling ----- LOG -------- "Virtual addresss ea880000" "Unable to handle kernel paging request at virtual address ea890000" -----LOG----- If you observe, virtual address of tcpm_base is ea880000. if ioremap() returns all contigious memory, There should be no dereferencing of "ea890000"(the max address should be ea88fffe) But in kernel logs show, it is dereferencing that address. My question now is... doesn't ioremap() returns contigious address space? With regards, Sandeep Kumar Anantapalli,

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