August 2011 - kernelnewbies@kernelnewbies.org

difference between io_schedule() and schedule()
by Rajat Sharma Aug. 10, 2011

Aug. 10, 2011

Hi All, What is the difference between io_schedule() and schedule(), is io_schedule() more restrictive to shedule only I/O bound processes or it just favours I/O bound processes. Any documentation link would be great help. Thanks, Rajat

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Debugging Kernel Panic
by Zac Storer Aug. 10, 2011

Aug. 10, 2011

I'm using fedora 15, and just compiled 3.0.1 stable. I'm getting a kernel panic when I close my laptop lid and it goes into suspend. How should I go about debugging this? Are there error logs I can check? Is there some way I can debug the linux kernel image? I'm a complete newb to linux dev, so any help would be appriciated.

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Interrupt not getting re-enabled after handler is killed
by anish singh Aug. 10, 2011

Aug. 10, 2011

Intention: Wanted to modify the behavior of threaded interrupt handler not being called after the threaded_handler was killed. Reason: Well there is no reason as such but just want to see what all needs to be done to get this right.I know that what i am doing is completely wrong as i would get a strom of irq's and device will be unstable[1]. Modification: I thought if i remove the below line from exit_irq_thread function set_bit(IRQTF_DIED, &tsk->irqaction->flags); it would do.But nothing happened then i inspected closely i found that in-case we need to do that we have to again create kthread which i am not doing in-case we again receive the interrupt of the killed threaded_handler. So i came to this conclusion: Right now we need more that just setting the flag bit to get this right. Is the above right ?Yes/no? Or if my understanding is not right then probably the interrupt controller itself is not sending the interrupt after the thread is killed.If this is right where is the code for that? In my limited search i couldn't find where we are disabling the interrupt once the threaded_handler is killed. Hope i am clear about what i want to know. [1] http://thread.gmane.org/gmane.linux.kernel/811061

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About HPET is_hpet_capable()
by limp Aug. 9, 2011

Aug. 9, 2011

Hi all, I am having a deeper look on Linux hpet code and I was wondering how exactly is_hpet_capable() works. >From the name of it, I assume that this function checks if the system supports HPET or not but I can't really tell how it does that. The function is the following: static inline int is_hpet_capable(void) { return !boot_hpet_disable && hpet_address; } Could anyone help me understand how this works? Regards.

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kallsyms_lookup_name
by Venkatram Tummala Aug. 9, 2011

Aug. 9, 2011

Hi, I need to use some unexported kernel symbols in my kernel module but in the particular kernel version i am based on (2.6.18 - RHEL 5.7), kallsyms_lookup_name is not exported and there is no kallsyms_on_each_symbol in this kernel. And I can't change the kernel owing to reasons i have no control over. In this scenario, how do i use unexported symbols. Is there any other mechanism by which i can lookup the address of a kernel symbol. Thanks. Venkatram

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new kernel boot
by Amirali Shambayati Aug. 8, 2011

Aug. 8, 2011

Hi all, I successfully installed new kernel but as new kernel is going to boot, I receive this error: FATAL:could not load /lib/modules/2.6.32.43kerneltest/modules.dep : No such file or directory I checked /lib/modules/2.6.32.43kerneltest directory, and modules.dep exists! Any guidance how can I solve the problem? Thanks in advance, -- Amirali Shambayati Bachelor Student Computer Engineering Department Sharif University of Technology Tehran, Iran

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xx_initcall ( ) in kernel
by sumeet linux Aug. 8, 2011

Aug. 8, 2011

Dear friends, I want to know the basics xx_initcall ( ) in linux kernel. How this function works ? Observed in kernel code, many places late_initcall ( ), early_initcall ( ), arch_initcall ( ), core_initcall ( ) gets called. When did all these functions gets call during kernel initialization ? I am more interested in what is the sequence of these functions gets called one after another. Thank you. Regards, Sumeet

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Creating sparse file on XFS and EXT3 has different results
by Ashish Sangwan Aug. 8, 2011

Aug. 8, 2011

I write 1 program to create sparse file which contains alternate empty blocks and data blocks. For example block1=empty, block2=data, block3=empty ..... #define BLOCK_SIZE 4096 void *buf; int main(int argc, char **argv) { buf=malloc(512); memset(buf,"a",512); int fd=0; int i; int sector_per_block=BLOCK_SIZE/512; int block_count=4; if(argc !=2 ){ printf("Wrong usage\n USAGE: program absolute_path_to_write\n"); _exit(-1); } fd=open(argv[1],O_RDWR | O_CREAT,0666); if(fd <= 0){ printf("file open failed\n"); _exit(0); } while(block_count > 0){ lseek(fd,BLOCK_SIZE,SEEK_CUR); block_count--; for(i=0;i<sector_per_block;i++) write(fd,buf,512); block_count--; } close(fd); return 0; } Suppose, I create a new_sparse_file using this above code. When I run this program, on ext3 FS with block size 4KB, ls -lh shows size of new_sparse_file as 16KB, while du -h shows 8 kb, which, I think is correct. On xfs, block size of 4kb, ls -lh shows 16KB but du -h shows 12kb. Why are there different kinds of behavior? If I increase the block_count to be written so that a 200MB file is created, on XFS du -h shows 187MB and on EXT3 it shows 101MB.

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Re: Creating sparse file on XFS and EXT3 has different results
by Greg Freemyer Aug. 8, 2011

Aug. 8, 2011

There are no "specs" as to how a sparse file is handled in response to writes. Sparse is mostly beneficial when the holes are very large. If an app really wants to have minimal on disk space, you should pre-allocate space with fallocate. You may even need to hole punch after the writes. Both xfs and ext4 support both fallocate and hole punching. (I don't know the userspace call to hole punch. I think its a relatively new feature for ext4.) Greg On Aug 4, 2011 10:16 PM, "Ashish Sangwan" <ashishsangwan2(a)gmail.com> wrote:

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MSI-edge in /proc/interrupts
by J.Hwan Kim Aug. 8, 2011

Aug. 8, 2011

Hi, everyone When I read /proc/interrupts, it displays interrupt type of my ethernet card with "MSI-edge". Does it mean MSI-X interrupt or MSI interrupt? I set to my ethernet driver operates with MSI-X interrupt. Thanks in advance. Best Regards, J.Hwan Kim

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