January 2012 - kernelnewbies@kernelnewbies.org

Regarding fat filesystem -- formats
by Sathishkumar Duraisamy Jan. 31, 2012

Jan. 31, 2012

Hi, I am getting following error in my target hardware when I trying to write, usb mass storage device having vfat file system. But at the same time I am to copy from the usb mass storage device. I have configured as iso8859-1 iocharset in the menuconfig. I am using Linux Kernel v2.6.30. Can you please give some clues how to fix this? FAT: Filesystem panic (dev sda1) fat_get_cluster: invalid cluster chain (i_pos 0) File system has been set read-only -- Regards, Sathishkumar D http://flowersopenlab.weebly.com/

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Using tasklist_lock in a module -- is there an alternative?
by Arokux B. Jan. 31, 2012

Jan. 31, 2012

Hi, For learning purposes I would like to iterate through all the processes in a module and output different information about them. For this task I need to lock the list of all tasks. I've seen some example in the kernel code which lock tasklist_lock. However this symbol cannot be used by modules. Is there any other way I can lock the list of tasks then? Thanks

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How to debug?
by Jalil Karimov <jukarimov＠gmail.com> Jan. 30, 2012

Jan. 30, 2012

As I learn C, I decided to write a small dictionary program, for my linux box. Unfortunatly, I'm unable to proceed because of that weird bug which I can't debug (no source of crash). Any help is appreciated. strace: read(3, "\270) file box\n 3) \321\200\320\260\320\267\320\263. \320\277\321\200\320\265"..., 4096) = 4096 read(3, "mixture of vodka and beer\n", 4096) = 26 read(3, "", 4096) = 0 close(3) = 0 munmap(0xb7860000, 4096) = 0 write(4, "\320\275\320\276-\320\266\321\221\320\273\321\202\321\213\320\271@11618255\n\321\217\320\270\321"..., 3875) = 3875 close(4) = 0 munmap(0xb785f000, 4096) = 0 --- SIGSEGV (Segmentation fault) @ 0 (0) --- +++ killed by SIGSEGV +++ gdb: Program received signal SIGSEGV, Segmentation fault. 0x80d15d70 in ?? () valgrind: ==11809== Memcheck, a memory error detector ==11809== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al. ==11809== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info ==11809== Command: ./dic -u ==11809== Parent PID: 1662 ==11809== ==11809== Jump to the invalid address stated on the next line ==11809== at 0x80D15D70: ??? ==11809== Address 0x80d15d70 is not stack'd, malloc'd or (recently) free'd ==11809== ==11809== ==11809== Process terminating with default action of signal 11 (SIGSEGV) ==11809== Access not within mapped region at address 0x80D15D70 ==11809== at 0x80D15D70: ??? ==11809== If you believe this happened as a result of a stack ==11809== overflow in your program's main thread (unlikely but ==11809== possible), you can try to increase the size of the ==11809== main thread stack using the --main-stacksize= flag. ==11809== The main thread stack size used in this run was 8388608. ==11809== ==11809== HEAP SUMMARY: ==11809== in use at exit: 70 bytes in 2 blocks ==11809== total heap usage: 426,629 allocs, 426,627 frees, 224,953,822 bytes allocated ==11809== ==11809== LEAK SUMMARY: ==11809== definitely lost: 70 bytes in 2 blocks ==11809== indirectly lost: 0 bytes in 0 blocks ==11809== possibly lost: 0 bytes in 0 blocks ==11809== still reachable: 0 bytes in 0 blocks ==11809== suppressed: 0 bytes in 0 blocks ==11809== Rerun with --leak-check=full to see details of leaked memory ==11809== ==11809== For counts of detected and suppressed errors, rerun with: -v ==11809== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 20 from 7)

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Tool for automatic style of coding guidelines
by Prajosh Premdas Jan. 30, 2012

Jan. 30, 2012

Hi I have developed some kernel drivers and would like to send the patches for review. But i find that I have not followed the coding guideline for tabs and spaces properly, which can be easily corrected by using some tools like astyle. Can any body please help me with the proper commands string for the astyle tool? Or could any body please suggest me with any new tool like indent etc which you are using -- Regards, Prajosh Premdas

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kmalloc before kmem_cache_init
by Sukanto Ghosh Jan. 29, 2012

Jan. 29, 2012

I am kind of lost trying to figure out how can kmallocs work if they are called before kmem_cache_init (e.g. such a case occurs when in start_kernel() we call parse_early_param() (which in turn might call early_serial8250_setup() if earlycon= is used in kernel command-line) before mm_init() (which later calls kmem_cache_init() ) >From what I understood, kmalloc() (SLUB implementation) first tries to find out the slab fit for the size being kmalloced and slabs are nothing but kmalloc_caches[]. Now these kmalloc_caches get initialized in kmem_cache_init(). What am I missing here ? Regards, Sukanto Ghosh -- Regards, Sukanto Ghosh

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Recursive Makefile howto
by Manavendra Nath Manav Jan. 28, 2012

Jan. 28, 2012

Hi All, I have developed a Makefile which recursively builds the code spread across multiple directories, each having it's own Makefile. build_all: targetA \ targetB \ target C Now, the problem is that even when the Makefile of targetA fails, the master Makefile continues building with targetB and targetC. I can also see the make errors being printed on console. I want the make to stop immediately at the first error encountered in any target Makefile. How to do this? -- Manavendra Nath Manav

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Re request_threaded_irq
by Asutosh Das Jan. 26, 2012

Jan. 26, 2012

Hi I have a query regarding the difference between request_irq and request_threaded_irq. I am aware that the thread_fn_handler may sleep, allocate memory, acquire locks etc. What context does the thread fn passed to the request_threaded_irq run in ? TIA -- ~/asd

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RO/NX Protections and Modules
by Dannie Stanley Jan. 25, 2012

Jan. 25, 2012

Regarding the source code for kernel version 2.6.38. In kernel/module.c the function defined as: SYSCALL_DEFINE3(init_module...) Calls set_section_ro_nx for core and init. My first question is this: Q1: Why doesn't the exit text/data get the RO/NX page protection? In the set_section_ro_nx function the RO comment reads: "Do not protect last partial page" and the NX comment reads: "Do not protect first partial page." In the presence of mixed pages this makes sense. However, change_page_attr_set_clr seems to check for page alignment. So my second question is this: Q2: Does the RO/NX only apply to page aligned sections? Thank you, Dannie -- Dannie M. Stanley

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What is a console? and Why it is always associated with UART?
by sandeep kumar Jan. 25, 2012

Jan. 25, 2012

Hi All, I want to know "What is a console? and Why it is always associated with UART?" What is a serial console?? Can there be a USB console?? I am getting to read these words associatedly.. Please help me understand them individually... -- With regards, Sandeep Kumar Anantapalli,

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serial: 8250: RX hang issue
by Pradeep Kumar Jan. 25, 2012

Jan. 25, 2012

Hi All, I am working on a mobile development platform and performing some stress warm boot tests using UART debug console(which is using serial 8250 driver for console). I am getting device debug console UART RX hang after iterations > 1500. after this issue am not* able to issue any command. Able to see logs though. Later I kept some debug prints in isr and able to see that device is able to generate interrupts when some data is received. So I came to conclusion that some malfunctioning is happening in upper layer not sure which layer has this problem. Can some one give some ideas at which layer I can check? One more observation is when I perform a open and close calls on debug UART port(in my case ttyS0) while device is in UART RX hang state, then I notice the UART console RX again below active and able issue commands from UART console itself.

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