October 2011 - kernelnewbies@kernelnewbies.org

print contents of runqueue
by kashish bhatia Oct. 19, 2011

Oct. 19, 2011

Hi, I want to print contents of runqueue of my current processor. I got the pointer to current task_struct. To get runqueue, I called task_rq(). When compiled the module, it gave an error. Actually struct runqueue and task_rq() is not in any header file. It is present in kernel/sched.c Is there any way to access this structure without making changes to kernel . -- Regards, Kashish

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Heap memory is not re-claiming.
by V.Ravikumar Oct. 18, 2011

Oct. 18, 2011

Hello all, I've a daemon process and I'm allocating heap memory** for big character buffers using malloc/free. Each can take 5MB. Though I freed/deleted memory allocated for the buffers, the increased memory during the allocation time is not re-claiming back.This I observed using *top* command. I'm sure I do not have any other memory leaks. I debugged the code line by line and observing memory usage using *top* command. During allocation time, *top* command showed that 30 MB increase in Virtual & Resident memory. Upon execution of delete/free statement on the buffers the raised memory was not re-claimed. On subsequent execution of the same code no extra memory was allocated even though new/malloc statements called on the buffers.What is kernel mechanism here. Is this due to some page cache re-mapping If this due to page cache then the memory should always constant trough out process life. During long run the memory slowly increasing. This should not happen. Could some body provide any insights into this.. Regards, Ravi

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Linux System Calls vs writing device drivers
by Ashok Sharma Oct. 17, 2011

Oct. 17, 2011

Hello, I am interested in writing Linux device drivers (DD) and have knowledge of OS concepts, Linux OS design and System Calls. What is the path to writing DD and please give some references/links. Thank you and regards Ashok

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Question about USB gadget driver usage
by Mikhail Boiko Oct. 17, 2011

Oct. 17, 2011

Hi We have linux-2.6.35 based device. Device has removable SD-card, which by certain condition is shared to PC vis USB connection using g_file_storage driver. Everything if fine, but when I manualy eject sd-card from cardholder, on my linux host machine, sd-card partition is still being mounted. In sources, there is a note, that if pass 'removable' parametr to g_file_storage module, locations specified by 'file' argument could be unmounted from sysfs by writing zero string to 'file'. But when try to do so, removal attempt is rejected in drivers/usb/gadget/storage_common.c:fsg_store_file() by first if-condition. 755 if (curlun->prevent_medium_removal && fsg_lun_is_open(curlun)) { 756 printk("eject attempt prevented\n"); 757 return -EBUSY; /* "Door is locked" */ 758 } As far as I understand, my host-pc blocks driver to eject certain LUN. Here is my parametrs to insert module insmod /lib/modules/g_file_storage.ko stall=0 removable=1 file=/dev/mmcblk0p4,/dev/mmcblk1p1 ro=0,0 where /dev/mmcblk0p4 is device internal memory (chip is soldered to pcb, so it can not be ejected) and /dev/mmcblk1p1 is removable sd-card Is there any way to perform `force eject` for one of my LUNs ? Thank you

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calculating ring buffer size
by Amit Nagal Oct. 17, 2011

Oct. 17, 2011

Hi , While going through a few usb drivers code , i observed that the drivers maintain a ring buffer which stores data coming from usb device in interrupt context . Also these ring buffers is a power of 2 size i am looking for reasons how to compute the the max size of these ring buffers , so that no overflow situation happens . What factors should always be accounted while computing the max size of these ring buffers . Regards Amit Nagal

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sample USB Driver / Probe not getting called
by Abhijit Pawar Oct. 17, 2011

Oct. 17, 2011

Hi All, Is there any way to call a sample USB driver whenever a USB device is attached to the system irrespective of the class and type of the device? To do this, LDD3, chap 13 mention that for USB device table, we only need to add the driver_info entry as 42. However if I do this, my probe is never getting called. Now, I give the vendor and product id of this Mouse to the device_id table and load my driver again. Still the probe is not getting called. Is it that USB core is getting the proper driver for this mouse before my driver entry in the list? Am I missing something? Regards, Abhijit Pawar

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power profiling ( /proc/acpi/processor .. missing)
by pankaj singh Oct. 17, 2011

Oct. 17, 2011

Hi, I am trying to do power profiling of my laptop (DELL LATITUDE) where i am using ubuntu 11.10. For this i m using powertop and acpitool but unfortunately i am not able to get C and P states. when i run `acpitool -c` it says Function Show_CPU_Info : could not read directory /proc/acpi/processor/ Make sure your kernel has ACPI processor support enabled. I have already check the config file ACPI_PROCESSOR is enable(in kernel). So do i require to install any specific driver to get C and P states. For information i m using kernel version 3.0.0-12-generic. -- Pankaj SIngh Phone No: 9921865080

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why does the 'break_lock' field of spinlock exist for preemptive kernel?
by Parmenides Oct. 16, 2011

Oct. 16, 2011

Hi, I am reading the source code of spinlock and have a question about it. The spinlock is defined as: typedef struct { volatile unsigned int slock; #ifdef CONFIG_PREEMPT unsigned int break_lock; #endif } spinlock_t; When 'break_lock' is one, it indicates that there are other tasks waiting the spinlock. If so, these tasks should be running on other CPUs. In other words, there are definitely no other tasks waiting the lock, which are on the same CPU on which the spinlock owner is runing, because the owner has disabled the kernel preemption. That is, there are no other local tasks which can set 'break_lock' to 1. Therefore, I think whether or not 'break_lock' is defined has nothing to do with CONFIG_PREEMPT. May be a misunderstanding. Any explanation?

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hello dick
by bob jonny Oct. 16, 2011

Oct. 16, 2011

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How to compile an older kernel?
by Parmenides Oct. 16, 2011

Oct. 16, 2011

Hi, I am using lfs which runs kernel 2.6.34, gcc 4.1.2 and ld 2.17. For some purposes, I want to compile the 2.6.11 kernel source. After doing some configuration, I did make which issues many warnings or error messages. For some of them: ... ... ... In file included from include/asm/mpspec.h:5, from include/asm/smp.h:18, from include/linux/smp.h:19, from include/linux/sched.h:25, from arch/i386/kernel/asm-offsets.c:7: include/asm/mpspec_def.h:78: warning: 'packed' attribute ignored for field of type 'unsigned char[6]' CHK include/asm-i386/asm_offsets.h UPD include/asm-i386/asm_offsets.h CC init/main.o ... ... ... In file included from include/asm/mpspec.h:5, from include/asm/smp.h:18, from include/linux/smp.h:19, from include/linux/sched.h:25, from arch/i386/kernel/process.c:17: include/asm/mpspec_def.h:78: warning: 'packed' attribute ignored for field of type 'unsigned char[6]' {standard input}: Assembler messages: {standard input}:909: Error: suffix or operands invalid for `mov' {standard input}:910: Error: suffix or operands invalid for `mov' {standard input}:1121: Error: suffix or operands invalid for `mov' {standard input}:1122: Error: suffix or operands invalid for `mov' {standard input}:1199: Error: suffix or operands invalid for `mov' {standard input}:1200: Error: suffix or operands invalid for `mov' {standard input}:1275: Error: suffix or operands invalid for `mov' {standard input}:1276: Error: suffix or operands invalid for `mov' {standard input}:1366: Error: suffix or operands invalid for `mov' {standard input}:1378: Error: suffix or operands invalid for `mov' make[1]: *** [arch/i386/kernel/process.o] Error 1 make: *** [arch/i386/kernel] Error 2 I think it is no problem to use newer compiler to compile older kernels. But, it seems that this is not really the case. To compile the 2.6.11 kernel, what do I need to adjust my system?

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