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

Re: Need basics of booting process
by Rigved Rakshit July 11, 2011

July 11, 2011

> > I want to know the basics linux booting process. I googled for this but i > didn't find the detailed things anywhere. I want to know the boot process > including the hardware work flow. Can anyone give me the detailed tutorial > to learn about this. > > First, when you power up the system the bios goes through a POST, which is > power-on self test. This just checks that hardware is working, etc. Then it > looks for a boot sektor, which must be 512 bytes long and end with a magic > number, and loads the kernel. From there, you can look at the head.s > assembly, and I think someone posted a tutorial here a while back--maybe > they'll post that again. > 1. The POST (Power-On-Self-Test) is done. POST checks all the processors that are connected, the amount of RAM available, disks that are connected, network cards available etc. 2. Then the BIOS (Basic Input/Output Services) program is loaded. The BIOS searches for IDE, SCSI, PATA drives. Then it searches for active (bootable) partition(s). Using this knowledge, it checks the information in the Master Boot Record (MBR) of the drive (that has the active partition(s)). Then, it loads the bootloader (mostly GRUB - Grand Unified Bootloader) from the MBR. 3. Grub knows how to read all kinds of partitions. So, it can boot from any file system. 1. It checks and loads the settings in /boot/grub/grub.conf. This file contains path for root = (hd0,0), kernel = vmlinuz, initrd = initrd.img (cpio archive). 2. The Linux kernel is loaded into the RAM. It knows how to unpack the cpio archive which was specified by initrd parameter in grub.conf. The kernel loads this unpacked initial RAM disk and root file system (also called initramfs) into the RAM. Then it starts executing the /etc/init file present in this initramfs. 1. initrd: It contains the initial RAM disk and the initial root file system. These are loaded into the RAM before the actual root file system from the hard disk is loaded. 2. ntldr: In case another bootloader is required to be loaded, then the 'chainloader+1' command tells grub to load the bootloader mentioned. ntldr is the Windows bootloader. In Windows, all drives are loaded in user-space. 4. init starts populating /dev with the devices that are connected. init inserts kernel modules (.ko files) to detect the connected hardware. 1. init loads the hard disk. Then, init "switches root" to the root file system in the hard disk. Finally, before terminating, this init file of the initramfs passes control to the init file in the hard disk. 2. init loads the partitions which are mentioned in /etc/fstab. 3. Then, all the files up to and including the required "init level" are executed. 1. These include rc.sysinit, rc.local (directory) and rcX.d (directory - where X refers to a whole number). 2. If you check the /etc/rc0.d directory, you will find symlinks starting with either a 'K' or a 'S'. This is followed by a number. This convention is followed purposely. All symlinks with a starting K are 'kill' commands. All symlinks with a starting S are start commands. All the symlinks are followed in lexicographic order. So, all the kill commands are executed first (K00*, K01* etc.), followed by the start commands (S00*, S01* etc.). 3. So, if you want to boot to init level 1, then all the commands in /etc/rc1.d directory are executed. If you want a Graphical Environment (i.e., init level 5), then all commands from rc1.d up to rc5.d are executed. 4. init level 0 is for shutdown and init level 6 is for restart (i think; not sure about init level 6). This is a brief introduction to the boot process. Modern OSs require much more than these basic things. Also, this boot process refers to the SysVInit model. Then is another model used by Upstart, which Ubuntu uses. Watch this video to learn more about Upstart: http://www.youtube.com/watch?v=ssnZBQqnze8 Hope this helps! Rigved Rakshit

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Re:Interview question
by Bond July 11, 2011

July 11, 2011

On Tue, Jul 5, 2011 at 9:33 PM, Greg Freemyer <greg.freemyer(a)gmail.com> wrote: > On Tue, Jul 5, 2011 at 9:43 AM, Mandeep Sandhu > <mandeepsandhu.chd(a)gmail.com> wrote: >>> Let me simplify the question. >> >> I'll attempt to answer your questions...for my own edification! :) >> >>> >>> 1) What are the FIVE classic system calls for interfacing with a >>> character device. (ie. If it did not exist in 1970, don't list it). >> >> open/close/read/write/seek?...and the infamous ioctl. > > You listed 6. Historically character devices don't seek. So drop > that one to get to 5. > > (And yes, you can find char devices that implement seek, but ioctl is > far more common. And when I learned UNIX 30 years ago, it was just > the basic 5 I'm pretty sure that actually have matching driver code..) > > That is, drivers don't implement seek. seek() just sets a offset > variable tracked in the kernel. The driver is not even woken up when > the happens. > > That is if userspace did: > > open() > seek(1) > seek(2) > seek(3) > write() > > The driver would get invoked for open, and again for write. The thing which he wanted to go in depth was why and how will the drivers open() ,write() get invoked. I tried my attempt that depending upon vendor and device id register_chrdev will have registered etc. My guess is he probably wanted to know the system call routine that will get executed with these open and close in kernel space. i.e. for example __NR_open() ,__NR_read() and the system call numbers that would get involved in this process.

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Linux Scheduler Statistics
by Vipin July 11, 2011

July 11, 2011

Hi All, Posting it from my parallel question at LQ http://www.linuxquestions.org/questions/linux-kernel-70/proc-schedstats-sta… I am trying to understand the statistics posted by /proc/schedstat. The documentation I could find on the subject was taken from here: Linux Scheduler Statistics http://eaglet.rain.com/rick/linux/sc...format-15.html I am running a FC14 2.6.35.6-45.fc14.x86_64 Below is a dump for my statistics version 15 timestamp 4356814703 cpu0 46540 0 96049852 39682767 50849563 28504181 6402127420973 1547256962507 55119801 domain0 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000003 22495 21765 675 1037826 94 33 0 21765 5797 5345 416 1801124 55 0 1 5344 757236 702579 46725 114900414 9212 244 119 702460 44 13 31 0 0 0 0 0 0 375257 21494 0 domain1 00000000,00000000,00000000,00000000,00000000,00000000,00000000,0000000f 5593 4668 737 2285778 273 25 7 4661 5790 5750 34 266075 19 0 7 2801 374455 353235 19119 49007529 2851 30 4416 348819 17 4 13 0 0 0 0 0 0 93063 4192 0 ... Removed the rest of the cpu/domains Can somebody please explain me that why my cpu fields (2-4) are not zero as suggested in the document ? Am I doing something wrong ? or are the results different for x86 & x86_64 boxes? Thanks. (P.S. I am running an i5 with 4 cores) Linux Boot process - somebody asked for it as I checked the archives http://www.opensourceproject.org.cn/article.php?id=182 Read Appendix A Thanks, Vipin Jain

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Problem in compiling a kernel module
by Ponkumaran Annadurai July 10, 2011

July 10, 2011

I am trying to compile a sample hello world module, but when issue make command, it says that "make: Nothing to be done for `all'.". Also I tried the command "make hello", then it is showing that "linux/module.h no such file". But I am in the newly compiled kernel. What might be the problem? -- thanks, kumaran

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timer problem
by Prashant Shah July 10, 2011

July 10, 2011

Hi, I am test out a simple schedule_timeout() code. When I insert the module kernel goes in a infinite loop printing this in the log : Jul 6 22:04:35 ubuntupc kernel: [ 5738.281659] Pid: 0, comm: swapper Not tainted 2.6.35-22-generic #33-Ubuntu Jul 6 22:04:35 ubuntupc kernel: [ 5738.281663] Call Trace: Jul 6 22:04:35 ubuntupc kernel: [ 5738.281671] [<ffffffff8104d15a>] dequeue_task_idle+0x3a/0x50 Jul 6 22:04:35 ubuntupc kernel: [ 5738.281679] [<ffffffff81052d6a>] dequeue_task+0x9a/0xb0 Jul 6 22:04:35 ubuntupc kernel: [ 5738.281687] [<ffffffff81052dae>] deactivate_task+0x2e/0x40 Jul 6 22:04:35 ubuntupc kernel: [ 5738.281693] [<ffffffff81586ba9>] schedule+0x4a9/0x830 Jul 6 22:04:35 ubuntupc kernel: [ 5738.281702] [<ffffffff81008ddb>] cpu_idle+0xeb/0x110 Jul 6 22:04:35 ubuntupc kernel: [ 5738.281710] [<ffffffff815832ad>] start_secondary+0x100/0x102 Any ideas on what is going on ? ---------------------------------- <testmod.c> ---------------------------------- #include <linux/kernel.h> #include <linux/module.h> #include <linux/init.h> #include <linux/timer.h> #include <linux/delay.h> #include <linux/sched.h> struct timer_list tim; void timfunc(unsigned long data) { printk("hi this is a timer %lu\n", data); set_current_state(TASK_INTERRUPTIBLE); schedule_timeout(10 * HZ); printk("hi again this is a timer after timeout %lu\n", data); } static int __init init_testmod(void) { init_timer(&tim); tim.expires = jiffies + HZ*5; tim.data = 1000; tim.function = timfunc; add_timer(&tim); return 0; } static void __exit exit_testmod(void) { printk("end of module\n"); return; } module_init(init_testmod); module_exit(exit_testmod); MODULE_LICENSE("GPL"); ------------------------------ </testmod.c> ---------------------------------- ---------------------------------- <Makefile> ---------------------------------- obj-m += testmod.o KERNELDIR ?= /lib/modules/$(shell uname -r)/build PWD := $(shell pwd) default: $(MAKE) -C $(KERNELDIR) M=$(PWD) clean: rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions depend .depend dep: $(CC) $(CFLAGS) -M *.c > .depend ifeq (.depend,$(wildcard .depend)) include .depend endif ---------------------------------- </Makefile> ----------------------------------

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Problem in building,installing new vanilla kernel - initramfs
by Vaibhav Jain July 10, 2011

July 10, 2011

Hi, For the past 2 weeks I have been trying to compile and install a new vanilla kernel (v2.6.39.2) on my debian and ubuntu vmware machines. But it is failing due to some problem related to initramfs. After compiling and installing the kernel and modules I am trying to create the initramfs image by using the command "update-initramfs -c -k 2.6.39.2". The command executes successfully and creates an initramfs image. However on booting the new kernel an error occurs and it takes me to the initramfs prompt. I tried it first on debian virtual machine and then on ubuntu virtual machine but failed on both. For building and installing the kernel I am NOT using any distribution-specific tools. Any help would be greatly appreciated. Thanks Vaibhav Jain

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Adding new function to existing driver ops
by Asha R July 8, 2011

July 8, 2011

Hi, I would like to know how to add new function to a driver in Linux Framework? For eg: In GPIO driver, there is gpio_chip structure defined. static struct gpio_chip mygpio_chip = { .label = "mygpio", .owner = THIS_MODULE, .direction_input = mygpio_direction_input, .get = mygpio_get, .direction_output = mygpio_direction_output, .set = mygpio_set, .to_irq = mygpio_to_irq, }; If i want to add *mygpio_pulldown* or *mygpio_altfunc* to support few more gpio functionalities, how and where can i add these functions in the structure? Any suggestions on this will be appreciated. Thanks in advance, Asha

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Re:Re: Query about UIO
by bill July 8, 2011

July 8, 2011

At 2011-07-08 02:37:46，"Hans J. Koch" <hjk(a)hansjkoch.de> wrote: >On Thu, Jul 07, 2011 at 07:15:25AM -0700, Greg KH wrote: >> On Thu, Jul 07, 2011 at 03:32:54PM +0800, bill wrote: >> > Hi, Greg >> > >> > I've been reading the UIO code, one place puzzled me a lot. >> > May I ask one question about it? >> > >> > ------------------------------------------------------------------------------- >> > drivers/uio/uio.c >> > static int uio_find_mem_index(struct vm_area_struct *vma) >> > { >> > int mi; >> > struct uio_device *idev = vma->vm_private_data; >> > >> > for (mi = 0; mi < MAX_UIO_MAPS; mi++) { >> > if (idev->info->mem[mi].size == 0) >> > return -1; >> > if (vma->vm_pgoff == mi) >> > return mi; >> > } >> > return -1; >> > } >> > >> > I don't get it why use vma->vm_pgoff as the index for struct uio_mem mem[MAX_UIO_MAPS], >> > Suppose there are twohardware memory space, if user intends to map the 2nd mem, then >> > the last parameter of mmap should be 1, >> > >> > mapaddr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, >> > fd, 1); >> > >> > Is my understanding correct? > >No, it isn't. The last parameter of mmap is divided by PAGE_SIZE before it >reaches the UIO core. Therefore, it has to be set to n * getpagesize(). >This is explained in the docs under Documentation/DocBook/. >Use "make htmldocs" to generate HTML documentation. A faster way is to do > >dblatex Documentation/DocBook/uio-howto.tmpl > >This generates a PDF with the UIO documentation, provided you have a working >LaTeX system, and have dblatex installed. > >Thanks, >Hans > Thanks for your explanation. So vma->vm_pgoff is not used as its original meanings, that's the point puzzled me. Now it's clear:) >> >> I really don't know, sorry. >> >> But Hans should know, Hans? >> >>

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Problem loading page in http://janitor.kernelnewbies.org/
by esmaeil mirzaee July 7, 2011

July 7, 2011

Hi I try to reach to link http://janitor.kernelnewbies.org/ but I've got error Problem loading page my connection is stable I can reach to other link but have problem with this page. Any suggestion is appreciate it. Thanks in advance. esmaeil PS: Apologize for weak in English and two times send.

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Query about UIO
by bill July 7, 2011

July 7, 2011

Hi, Greg I've been reading the UIO code, one place puzzled me a lot. May I ask one question about it? ------------------------------------------------------------------------------- drivers/uio/uio.c static int uio_find_mem_index(struct vm_area_struct *vma) { int mi; struct uio_device *idev = vma->vm_private_data; for (mi = 0; mi < MAX_UIO_MAPS; mi++) { if (idev->info->mem[mi].size == 0) return -1; if (vma->vm_pgoff == mi) return mi; } return -1; } I don't get it why use vma->vm_pgoff as the index for struct uio_mem mem[MAX_UIO_MAPS], Suppose there are twohardware memory space, if user intends to map the 2nd mem, then the last parameter of mmap should be 1, mapaddr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 1); Is my understanding correct? thanks bill

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