February 2013 - kernelnewbies@kernelnewbies.org

Why kernel uImage to be loaded at 32KB offset ?
by KARTHIK SEKURU Feb. 19, 2013

Feb. 19, 2013

Hi All, My board's physical memory starts at 0x8000_0000. The kernel uImage is loaded at 0x80008000. I have seen in many other boards the uImage is loaded at 32KB. Why is this mandatory to load uImage at 32KB offset? Please let me know. Thanks, Karthik.

2 1

Suppress all boot output (framebuffer?) - embedded linux distro
by Ivan Nikolaev Feb. 19, 2013

Feb. 19, 2013

Hi everybody! I'm new to linux kernel development (very very little experience), time ago have began studying Operating Systems, even written a simple x86 2-stage bootloader for my supa-dupa-noob-os (which never ended up in something working). Anyway, that was just to explain what kind of a noob you talk to. ;) I'm developing an ubuntu 12.04 (LTS) based embedded distribution, which basically is a normal ubuntu stripped down to bare minimal packages, which runs a minimal XOrg server with one single full-screen application. What I want is to suppress every single char of console output since the bootloader passed control to the kernel, and possibly show instead of that some static text and/or image. What I thought is to try to disable printk-s and to write some kind of patch which uses the framebuffer to show the logo. Is that possible/difficult? Can you eventually explain where I should dig? Thanks in advice!

2 1

Re: SIGKILL and a sleeping kernel module
by Kevin Wilson Feb. 19, 2013

Feb. 19, 2013

Hi, 1) changing to msleep_interruptible() did not change the situation. 2) What is strange is that I *do* see the printk messages of kernel_init/kernel_exit, but I do not see the printk messages in the thread function, thread_function() (also before the first mslee()/msleep_interruptible() ). And they are the same printk level; I also tried with printk(KERN_ERR.. in the thread_function(), but it did not help. Any ideas what can be the problem ? I will really appreciate if somebody will try to create a kernel thread and add printk inside the kernel method and look if it does print anything, Rgs, Kevin On Tue, Feb 19, 2013 at 1:38 PM, Srivatsa S. Bhat <srivatsa.bhat(a)linux.vnet.ibm.com> wrote: > On 02/19/2013 05:02 PM, Kevin Wilson wrote: >> Hi, >> >> Thanks about the info about ps. >> This raises two new questions: >> 1) The following code is a very basic kernel module (based on my >> previous code, removing somethings). >> I do not understand something: >> I call >> /* sleep for a millisecond */ >> msleep(1); >> printk("calling do_exit\n"); >> msleep(60000); >> >> In my understanding, after 1 millisecond, it should have been >> available to the scheduler, and after returning to the line after >> msleep(1), it should print "calling do_exit". However, >> I see no such log message. Any ideas why ? can something be >> added to enable this ? >> > > Are you sure your settings related to logging are fine? IOW, is this > the only print you are not seeing, or are you not seeing *any* > printk messages? > >> 2)How can I create a kernel thread so that it will be in >> TASK_INTERRUPTIBLE state ? there must be a way, >> since I see many kernel threads where ps shows "S" in the >> status coumn. >> > > Try using msleep_interruptible(). > > Regards, > Srivatsa S. Bhat > >> >> struct task_struct *task; >> >> int thread_function(void *data) >> { >> int exit_sig = SIGKILL; >> >> printk("in %s\n",__func__); >> /* sleep for a millisecond */ >> msleep(1); >> printk("calling do_exit\n"); >> msleep(60000); >> do_exit(exit_sig); >> >> return 0; >> } >> >> static int kernel_init(void) >> { >> printk("in kernel_init\n"); >> task = kthread_create(thread_function,NULL,"MY_KERNEL_THREAD"); >> return 0; >> } >> >> static void kernel_exit(void) >> { >> printk("in kernel_exit\n"); >> kthread_stop(task); >> } >> >> >> module_init(kernel_init); >> module_exit(kernel_exit); >> >> >> rgs >> Kevin >> >

2 1

How controll is passed from uboot to kernel
by Chetan C.R. Feb. 19, 2013

Feb. 19, 2013

Hi All, I need to know how the control is passed from u-boot to kernel in Linux operating system Thanks in Advannce

4 3

Tracing SIGKILL, is that possible?
by Daniel. Feb. 19, 2013

Feb. 19, 2013

Is there a way to track signals, specially SIGKILL. I would like to know if some process dies because reach some resource limit, because an OMM error or something likewise.. Cheers -- "Do or do not. There is no try" Yoda Master

3 2

Linux Kernel
by kapil agrawal Feb. 19, 2013

Feb. 19, 2013

Hi, How the linux kernel runs in the system after spawning the init and mounting the root FS. Does it run as some background process ? How it serves the system calls etc. ? Regards Kapil

3 4

Tracing - how can I know which method was called
by Kevin Wilson Feb. 18, 2013

Feb. 18, 2013

Hi, I added a network event trace thus: echo 1 > /sys/kernel/debug/tracing/events/net/net_dev_xmit/enable Afterwards I see many lines with net_dev_xmit in /sys/kernel/debug/tracing. Now, looking in the source code, I see that there are two calls to trace_net_dev_xmit() in dev_hard_start_xmit(). These invocations are identical. see: http://lxr.free-electrons.com/source/net/core/dev.c?v=2.6.37 Is there a way in which I can make the log say which of these invocations was called ? (without changing the dev_hard_start_xmit() method). rgs, Kevin

2 1

gdtr value
by horseriver Feb. 18, 2013

Feb. 18, 2013

hi:) The gdtr reg saves the base address of gdt , whether is this address a linear address or phisical address ? thanks!

2 4

RE: spinlock deadlock
by buyitian Feb. 18, 2013

Feb. 18, 2013

> Date: Mon, 18 Feb 2013 10:54:44 +0100 > From: tglx(a)linutronix.de > To: buyit(a)live.cn > CC: mulyadi.santosa(a)gmail.com; kernelnewbies(a)kernelnewbies.org; a.p.zijlstra(a)chello.nl; rabin(a)rab.in; mingo(a)kernel.org > Subject: RE: spinlock deadlock > > On Sun, 17 Feb 2013, buyitian wrote: > > Could you please use a mail client, which creates readable mail? > > > this patch is to prevent deadlock between rq->lock and > > logbuf_lock. i can understand this thanks to Rabin. 2. in patch > > 07354eb1a74d1e1ece29f8bafe0b46e8c77a95ef, Thomas did changes as > > below, which reverted the change from peter, i don't know why: in > > function console_trylock_for_printk(): > > > - spin_unlock(&logbuf_lock); > > if (wake) > > up(&console_sem); > > + raw_spin_unlock(&logbuf_lock); > > > and this change exists in the latest kernel source code. it seems > > that deadlock bewteen rq->lock and logbuf_lock comes back, who can > > explain this, thanks. BTW: if i place printk inside schedule(), i > > may get rq->lock before calling printk. > > That looks like a merge slipup. The patch which converts the lock is > not supposed to do any other changes. But the patch was based on an > older kernel version, which did not have Peters changes yet. So the > fixup of the not longer applying patch failed somehow. i will provide patch, thanks for your reply. > > Thanks, > > tglx

1 0

sizeof(int[1]) means what ?
by sdptroy3＠gmail.com Feb. 17, 2013

Feb. 17, 2013

hi, i'm reading the file ioctl.h, there i encountered a macro _IOC_TYPECHECK(t) which looks like: #define _IOC_TYPECHECK(t) \ ((sizeof(t) == sizeof(t[1]) && \ sizeof(t) < (1 << _IOC_SIZEBITS)) ? \ sizeof(t) : __invalid_size_argument_for_IOC) in this code ,what does sizeof(t[1]) mean? i mean the argument of this macro in a type(int, float), in that case what does sizeof(int[1]) specify? I have written a small test program which prints the value of the expression 4. Thank you

2 1