May 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

4 8

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

4 5

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.

4 14

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?

5 11

Getting started on Linux Kernel Development
by Daniel Hamacher June 3, 2013

June 3, 2013

Greetings. My name is Daniel and I am starting out in Linux Kernel development on a Debian Linux distribution. I followed the steps on kernelnewbies.org and I am booting now with 3.10.0-rc3+. So I build the compiler and I am also booting from it. I watched the video from Greg Kroah-Hartman on how to submit patches, I created a branch, so I am ready to go... How do I get started with the Kernel janitors to get my feet wet? I have intermediate knowledge of C and basic knowledge of Assembly. Is there anything in particular that I can get started on? Thanks. Cheers, Daniel

5 4

which function perform gso
by Varun Sharma May 31, 2013

May 31, 2013

Hi, which function perform Generic segmentation offload in kernel.

2 1

Memory leaks in Samsung's kernel
by Michał Akaanonim May 30, 2013

May 30, 2013

Hi, I'm developing custom kernel for my Samsung Galaxy Ace 2 phone. First, I'd like to check if there are any bugs, so I built kernel with kmemleak enabled and I get 10 entries, for example: unreferenced object 0xce2a2000 (size 8192): comm "vold", pid 1855, jiffies 4294942835 (age 1394.240s) hex dump (first 32 bytes): 00 00 00 00 24 7e 50 c0 d0 7d 50 c0 7c 7d 50 c0 ....$~P..}P.|}P. 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ backtrace: [<c03f4a00>] create_object+0x10c/0x24c [<c08e99f0>] kmemleak_alloc+0x6c/0xd0 [<c03f1a54>] __kmalloc+0x178/0x27c [<c0507988>] __crypto_alloc_tfm+0x4c/0x140 [<c05086b8>] crypto_spawn_tfm+0x78/0xcc [<c0511dc0>] crypto_cbc_init_tfm+0x2c/0x44 [<c05079dc>] __crypto_alloc_tfm+0xa0/0x140 [<c05086b8>] crypto_spawn_tfm+0x78/0xcc [<c050b968>] skcipher_geniv_init+0x2c/0x54 [<c050cd68>] eseqiv_init+0x50/0x54 [<c05079dc>] __crypto_alloc_tfm+0xa0/0x140 [<c050aee0>] crypto_alloc_ablkcipher+0x68/0xa8 [<c06b82b0>] crypt_ctr+0x294/0x8a0 [<c06b08c8>] dm_table_add_target+0xf8/0x260 [<c06b3ffc>] table_load+0x114/0x2c4 [<c06b37d4>] dm_ctl_ioctl+0x1d0/0x2cc I noticed that in 6 of 10 entries there are dm_ctl_ioctl, table_load and dm_table_add_target functions. So I think something is wrong with MD driver but I compared source of this driver with other find on net and there aren't any differences. Source code of my kernel can be found here: https://github.com/hckk/GT-I8160_Kernel Thanks for any help. Greetings, Michal.

3 2

File System Implementation
by Dibyayan Chakraborty May 29, 2013

May 29, 2013

Hi, I was implementing a file system and ran into the following problem. I wanted to replicate the super block data in order to recover from occasional Hard disk failures (bit rot problem etc.). While replicating was easy i could not find a way to detect the errors in the first place. Any ideas and explanation will be help full. -- With Regards Dibyayan Chakraborty

2 1

hi about C and asm
by lx May 29, 2013

May 29, 2013

hi all: They are some asm codes in the kernel like: #define set_bit(nr,addr) ({\ register int res __asm__("ax"); \ __asm__ __volatile__("btsl %2,%3\n\tsetb %%al": \ "=a" (res):"0" (0),"r" (nr),"m" (*(addr))); \ res;}) But, almost I can't understand this. So I want to understand asm in C, which book or website I should learn ? Thank you

3 2

abort when using memory returned by io_remap_pfn_range
by Brian Magnuson May 29, 2013

May 29, 2013

Hi, I'm attempting to export three regions of memory out to userspace via mmap and I've run into a total block. Of the three regions two are reserved areas of DRAM and the last is in IO space and represents configuration registers. The device is a Zynq-7000 Xilinx FPGA so it's a ARMv7 architecture. All three calls to *remap_pfn_range succceed, non-NULL pointers are returned to user space, and the two DRAM regions work fine but any attempt to access the IO region from a user program fails with: Unhandled fault: imprecise external abort (0xc06) at 0xb6fe9000 The code is below where ETA1_REGS_PHYS_OFFSET (the IO region) is 0x60E0_0000. I can mmap /dev/mem at this address and poke at it without any issues. So... any help on what I'm doing wrong here? I've spent the better part of two days on this and haven't a clue. Incidentally, I'm using memmap on the kernel command line to reserve the DRAM areas. I'm thinking maybe there's probably a better way to reserve large amounts of physically continguous memory? Thanks, -Brian static int eta1_mmap(struct file *filp, struct vm_area_struct *vma) { int ret, map; // mmap offset, size, physical memory address, IO static uint32_t maps[3][4] = { { ETA1_TX_BUFFER_VIRT_OFFSET, ETA1_TX_BUFFER_SIZE, ETA1_TX_BUFFER_PHYS_OFFSET, 1 }, //TX 64MB { ETA1_RX_BUFFER_VIRT_OFFSET, ETA1_RX_BUFFER_SIZE, ETA1_RX_BUFFER_PHYS_OFFSET, 1 }, //RX 64MB { ETA1_REGS_VIRT_OFFSET, ETA1_REGS_SIZE, ETA1_REGS_PHYS_OFFSET, 0 } //Regs 16KB }; for (map = 0; map < 3; map++) { if (vma->vm_pgoff == maps[map][0] >> PAGE_SHIFT) { if (vma->vm_end - vma->vm_start != maps[map][1]) { printk(KERN_ERR "Buffer %d size doesn't match\n", map); return -EAGAIN; } if (maps[map][3]) { //DRAM ret = remap_pfn_range(vma, vma->vm_start, (unsigned long)(maps[map][2] >> PAGE_SHIFT), vma->vm_end - vma->vm_start, vma->vm_page_prot); } else { //IO memory - This just a define to remap_pfn_range on ARM but let's be nice ret = io_remap_pfn_range(vma, vma->vm_start, (unsigned long)(maps[map][2] >> PAGE_SHIFT), vma->vm_end - vma->vm_start, vma->vm_page_prot); } return ret; } } printk(KERN_ERR "Didn't match base offset for any range\n"); return -EAGAIN; } user: void *mmap_wrap(int fd, size_t length, off_t offset) { void *regs; regs = mmap(NULL, length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, offset); if (regs == MAP_FAILED) { perror("mmap"); return NULL; } return regs; } int main(void) { int fd = open("/dev/eta1", O_RDWR | O_SYNC); if (fd == -1) { perror("Could not open device"); exit(-1); } uint32_t *regs; regs = (uint32_t *)mmap_wrap(fd, ETA1_REGS_SIZE, ETA1_REGS_VIRT_OFFSET); regs[0] = 0x1; //BOOM }

1 1