June 2013 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

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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Not able to get crash dump
by neha naik Aug. 6, 2013

Aug. 6, 2013

Hi All, I have loaded the linux crashdump on ubuntu machine. I can manually generate the crashdump by the 'echo c > /proc/sysrq-trigger'. However, i am having a panic in a module i have written, which is not generating a core dump. I simply see the stack in the console and it kind of hangs there. I have to manually power it off and power it on ... Can someone explain why this happens? Is it because the kernel has gone into such a state that it cannot even follow the procedure for crash dump. Regards, Neha

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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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Read BIOS
by Satya Prakash Prasad July 31, 2013

July 31, 2013

I am trying to write a code to read BIOS details. Below is the program but I believe that I am not reading BIOS details. Can anyone please correct me in my understanding: Note I found that /proc/ioports gives the I/O ports details like: [root@ioport]# cat /proc/ioports 0000-001f : dma1 0020-0021 : pic1 0040-0043 : timer0 0050-0053 : timer1 ........and so on.................. #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <sys/io.h> #include <ctype.h> #include <string.h> main(int argc, char *argv[]) { unsigned char c; if(argc != 2) { printf("-1. Invalid args : usage %s start-end address\n", argv[0]); exit(-1); } char * temp = argv[1]; while(*temp != '\0' && (isxdigit(*temp) || *temp=='-')) temp++; char * delim = strchr(argv[1], '-'); if(*temp != '\0' || !delim ) { printf("-2. Invalid args : usage %s start-end address\n", argv[0]); exit(-2); } *delim = '\0'; int start = (int)strtol(argv[1], '\0', 16), end = (int)strtol(delim+1, '\0', 16), index = 0; if(start < 0 || end <= 0 ) { printf("-3. Invalid args : usage %s start-end address\n", argv[0]); exit(-3); } if(iopl(3) == -1) { printf("-4. Unable to set privilege level\n"); exit(-4); } if(ioperm(start, end - start, 1) == -1) { printf("-5. Unable to set access permission bits\n"); exit(-5); } for(index = start ; index <= end ; index ++) { c = inb(index); printf("%X", c); } ioperm(start, end - start, 0); printf("\n"); } So my program dumps the data in-between the ports assigned for devices: [root@ioport]# ./a.out 0000-001f 01000007D0FFFFFFFFFFFFF0100000 7D0FFFFFFFFFFFFF Please let me know if I am in the right path or not and guide me appropriately. Regards, Prakash

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Filesystem and files getting corrupted
by Daniel Hilst Selli July 7, 2013

July 7, 2013

I'm working on an embedded project based on var-som-am35 from TI. [1] I experiencing a lot of corruption from files and even the entire filesystem... is there any guide on how debug filesystems corruption? We already tryied vfat and ext3 fs.. changed media, changed machines... The filesystem runs on mmc card, or on usb flash drive... There is a java aplication running on top of this filesystem, which uses JMS, that is very I/O agressive.. Cheers,

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On common struct clock in clock framework.
by mind entropy June 30, 2013

June 30, 2013

Hi, I am reading through mini2440 code and understanding the clocking code. I am getting confused as to whether it uses the common clocking framework. In https://github.com/torvalds/linux/blob/master/arch/arm/plat-samsung/include… they define a struct clk. Even in OMAP (http://processors.wiki.ti.com/index.php/Clock_Framework_User_Guide#Software…) they have a separate struct clk definition. In the common clocking framework shouldn't they be using the common struct clk rather than have their own versions of struct clk? Thanks in advance.

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Kernel Linux updating
by Mylene Josserand June 29, 2013

June 29, 2013

Hi everyone, I would like to know how the Linux Kernel are updated. I know that there is the long term kernels, the last stables and the mainline. First, what is the real difference between stable and longterm ? I see in the Linux Kernel website that the date of the long term (and the revision number) is changing so I was thinking that there are some updates on it, right ? For example, when an important bug has been fixed, is it fixed in the new release kernel only ? Or is it applied on old kernels ? Only the long term ? All ? So if I am using the long term 3.4.49 for example (and the current is 3.4.51), I can just update the 3.4.49 to get the important bugs fix that have been fixed in the new release (so 3.9.8 right now ?). And if you have some documentation about it, it would be nice ! Thank you in advance ! -- Mylène JOSSERAND

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Kexec drops to initramfs prompt
by Paul Davies C June 29, 2013

June 29, 2013

Hi, I am trying to use the kexec to load a compiled kernel in a virtual machine that is ran using qemu. Here are the steps that I followed. 1. Compiled kernel on my Ubuntu to create bzImage. 2. Copied this bzImage to the virtual machine(debian) 3. In the virtual machine, I created an initial ramdisk using the command *mkinitramfs -o initrd.img* 4. I loaded the image to the kernel using the command *kexec -l bzImage --append="`root=UUID=<string> ro quiet`" --initrd=initrd.img*. The append was done based on /proc/cmdline. 5. Now I did a *kexec -e * which after some warning messages dropped me in to an initramfs prompt. One of the warning read as follows */dev/disk/by-uuid/<string> * *does not exist.* Can you please tell me what I am doing wrong? Please note that I have *CONFIG_KEXEC=y *on my current kernel of debian VM . -- *Regards,* *Paul Davies C* vivafoss.blogspot.com

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kernel crash and dabt_svc
by Mohammed Shafi June 28, 2013

June 28, 2013

Hi, I am debugging a kernel crash in arm platform [ 486.447220] [<c000de98>] (__dabt_svc+0x38/0x60) from [<bf05c324>] (ath6kl_deliver_frames_to_nw_stack+0xac/0xf0 [ath6kl_core]) Does dabt_svc is similar to 'EIP' ? ath6kl_deliver_frames_to_nw_stack+0xac points to the exact offset (over gdb) gives the line of crash ? crash log [ 486.447220] [<c000de98>] (__dabt_svc+0x38/0x60) from [<bf05c324>] (ath6kl_deliver_frames_to_nw_stack+0xac/0xf0 [ath6kl_core]) [ 486.458520] [<bf05c324>] (ath6kl_deliver_frames_to_nw_stack+0xac/0xf0 [ath6kl_core]) from [<bf04a184>] (do_recv_completion+0x3c/0x60 [ath6kl_core]) [ 486.471692] [<bf04a184>] (do_recv_completion+0x3c/0x60 [ath6kl_core]) from [<bf04bac0>] (ath6kl_htc_pipe_rx_complete+0x5e0/0x670 [ath6kl_core]) [ 486.484563] [<bf04bac0>] (ath6kl_htc_pipe_rx_complete+0x5e0/0x670 [ath6kl_core]) from [<bf063f2c>] (ath6kl_core_rx_complete+0x10/0x14 [ath6kl_core]) [ 486.497816] [<bf063f2c>] (ath6kl_core_rx_complete+0x10/0x14 [ath6kl_core]) from [<bf08afd4>] (ath6kl_usb_io_comp_work_rx+0x34/0x7c [ath6kl_usb]) [ 486.510691] [<bf08afd4>] ( thanks in advance. regards, shafi

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pci_iomap() and pci_ioremap_bar()
by Warlich, Christof June 28, 2013

June 28, 2013

Hi, can anyone explain when I should use void __iomem *regs = pci_iomap(device, barNumber, 0); and when void __iomem *regs = pci_ioremap_bar(device, barNumber); is more appropriate to map PCI memory? Furthermore, after the mapping succeeded, when may I directly access the mapped memory, e.g.: char firstByte = *regs; and when should I better use ioread8() instead?: char firstBype = ioread8(regs); All listed alternatives from above seems to work equally well for me (on x86), so I'm curious to learn what might be the difference. A guess: Does ioread8() work for both memory mapped _and_ IO mapped registers, while the direct access only works for the memory mapped case? Thanks for any clarification.

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