March 2011 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

how does fork() copy threads of a process in multi-processor (SMP)
by lalit mohan tripathi March 11, 2011

March 11, 2011

I've a general question: In Multiprocessor (Multi-Core) (SMP) environment how does fork system call (do_fork() related code) maintain the synchronization in case the threads of a process are running on different processors? E.g. it can happen that the fork() is called by cpu-0 thread and other thread of same process is executing on cpu-1. I can see that copy of the process is made by do_fork() code in fork.c. Can anyone give more details how the concurrency issue gets handled e.g. how PC and Regs are of cpu-1 thread get copied without any race condition in SMP / multiprocessor system? Thanks in advance

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error: #error Unknown data abort handler type from glue.h file
by Madhavi Manchala March 10, 2011

March 10, 2011

Dear All, When I looked into the linux-2.6.36/arch/arm directory, I did not find the mach-s3c2510/s3c2510a directory for Samsung s3c2510a MCU. When I asked the same in the ARM forum, they told me that this MCU is a NO-MMU based MCU and in the current kernel there was no much support for it. For complete details, please look at the following link. http://comments.gmane.org/gmane.linux.ports.arm.kernel/108351 So, I started developing the architecture files for my MCU i.e. Samsung S3C2510A. However, when I am trying to build the kernel after adding the support for S3C2510A processor, I am getting the following error. CC init/main.o In file included from /home/madhavi/linux-2.6.36/arch/arm/include/asm/cacheflush.h:15:0, from include/linux/highmem.h:9, from include/linux/pagemap.h:10, from include/linux/mempolicy.h:70, from init/main.c:50: /home/madhavi/linux-2.6.36/arch/arm/include/asm/glue.h:119:2: error: #error Unknown data abort handler type make[6]: *** [init/main.o] Error 1 make[5]: *** [init] Error 2 make[5]: Leaving directory `/home/madhavi/linux-2.6.36' make[4]: *** [/home/madhavi/linux-2.6.36/.image] Error 2 When I looked into the sources of the /arch/arm/include/asm/glue.h file, none of the macro defines the CPU_DABORT_HANDLER. From the arch/arm/Makefile the abort handler for no-mmu based CPUs is as follows. obj-$(CONFIG_CPU_ABRT_NOMMU) += abort-nommu.o In my case, the CONFIG_CPU_ABRT_NOMMU is defined in .config file to y. My question is, why again it is trying to check the abort handler from glue.h file? Shall I add a new macro in the glue.h file for defining the CPU_DABORT_HANDLER based on this new MCU (Samsung S3C2510A)? Any ideas / hits would be appreciated. Thanks for your help. Regards, Madhavi M.

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Need an understanding on Bluetooth driver
by Tirtha Ghosh March 10, 2011

March 10, 2011

Hi All, I am really new to bluetooth s/w development. And need some idea how it works in linux system. As far as I know, Bluez protocol stack is available on Linux. Bluez drivers are already mainlined in Kernel and utilities are available for user-space. When we say bluez driver, what does it mean? Is it the bluetooth protocol stack? If so, then what user-space utilities contain? The BT chip can be connected via UART, USB or SDIO interfaces. Who communicate with these interfaces, is it bluez kernel drivers or user-space utilities (via sys or proc)? Finally, I saw this BT chips can support Toshiba stack or BlueSoleil or any other stack. Does bluez support any form of BT, regardless what protocol stack they are using?? Say, there is BT chip in form of USB dongle which can be connected via regular USB port to the system. Does this dongle may need specific driver in Linux or bluez driver can handle this dongle using normal USB drivers available in system?? I am not sure if I sound clear about my doubts. A small description about bluez architecture might clear my doubt. I am aware of linux kernel and device driver model, so you can be specific while describing this. TIA

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How to verify block numbers of file ?
by kashish bhatia March 8, 2011

March 8, 2011

Is there any method/command/utility to know what are the block numbers which are allocated to a file in ext2 fs? -- Regards, Kashish

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Regarding memory compaction
by solmac john March 8, 2011

March 8, 2011

Hi All, I am working on memory compaction. (http://lwn.net/Articles/368869/) and i wan't to test the same can some one guide how to test same or is there any sample application or utility to test memory compaction Thanks, Akhilesh

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From which point onwards the kernel execution starts
by AQ Tast March 8, 2011

March 8, 2011

Hello Everyone, I am studying bootloaders and wanted to know which function exactly the kernel starts from , i.e. where is the main function? I been through the init/main.c file and I think most likely this is the file. Could someone please explain how the kernel initializes, i.e. I want to know how does kernel starts from main function

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Trying to compile linux 2.6.38
by Ian Porter March 7, 2011

March 7, 2011

Hi All, I am trying to compile (from the ubuntu 11.04 source) But getting this error message ? /usr/src/linux-2.6.38/arch/x86/kernel/entry_64.S: Assembler messages: /usr/src/linux-2.6.38/arch/x86/kernel/entry_64.S:1544: Error: .size expression does not evaluate to a constant Any thoughts ? Cheers Ian

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Fwd: help with unknown symbols when trying to load kernel module
by julie Sullivan March 6, 2011

March 6, 2011

I found this query on linux-kernel. Can anyone help George? ---------- Forwarded message ---------- From: George Nychis <gnychis(a)cmu.edu> Date: Sun, Feb 27, 2011 at 5:26 PM Subject: help with unknown symbols when trying to load kernel module To: linux-kernel(a)vger.kernel.org Hi all, Long story short, I am trying to rebuild a kernel module for my android phone. Unfortunately, Motorola did not post the kernel configuration they used (https://opensource.motorola.com/sf/sfmain/do/viewProject/projects.droid - I am running 2.2.1). They also did not configure the kernel to dump it at /proc/config.gz. I have the exact source code used to build both the kernel, and the wireless kernel module used. But again, I do not have the exact kernel configuration. Therefore, I do not want to replace the kernel on the phone (in fear of misconfiguration causing boot errors), I simply want to rebuild the wireless module and get it to work with the kernel already on the phone. I've tried getting help from the android community, however their kernel mailing list only gets about 3 messages a day and posts are moderated and lag behind something like 4 days. So, I'm hoping for a little bit of help here on the linux end of things from the linux community. I've ballparked the configuration using an older configuration file posted on another forum, and was able to successfully build my own kernel (albeit I do not use it), and then also build the wireless module successfully. When I try to load the module on the phone, I get a pretty long list of undefined symbols: http://pastebin.com/re5mRj4E I decided to start by focusing on one of these errors, 'register_netdev' and used 'nm' on my kernel module and found that it is undefined: 00073b60 T regReadLastDbgState U register_netdev 000345ec T regulatoryDomain_SetDefaults Here is the entire nm output: http://pastebin.com/8kTDKF87 I'm a little confused as to what this means. Does this mean that the stock kernel on the phone does not have this symbol? It seems odd since I believe the wireless module requires it. Or does it mean something else? Thanks for any help. I'm also not registered on the mailing list, so if you could CC me on any responses I would sincerely appreciate it. - George -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/

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writing a module to expose information
by Littlefield, Tyler March 6, 2011

March 6, 2011

Hello all: I'm curious what or where I might begin writing a module that will allow a program to retrieve information from it? Essentially: I need some sort of interface through which I can request information and get it returned somehow. -- Thanks, Ty

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about printk and console_loglevel
by Siddu March 6, 2011

March 6, 2011

Hi all, Hi all, I am little stuck understanding this piece of code below and the way its been working Question: since KERN_INFO = 6 # which is msg_log_level and as per code *msg_log_level < console_loglevel* this line of printk is not supposed to show up in the dmesg log ? but it is showing up . Why cat /proc/sys/kernel/printk 4 4 1 7 console_loglevel = 4 printk(KERN_INFO "Brought up %ld CPUs\n", (long)num_online_cpus()); static void _call_console_drivers(unsigned start, unsigned end, int msg_log_level) { if ((*msg_log_level < console_loglevel* || ignore_loglevel) && console_drivers && start != end) { if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) { /* wrapped write */ __call_console_drivers(start & LOG_BUF_MASK, log_buf_len); __call_console_drivers(0, end & LOG_BUF_MASK); } else { __call_console_drivers(start, end); } } } Thanks for any inputs ! -- Regards, ~Sid~

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