December 2011 - kernelnewbies@kernelnewbies.org

where to check Kthread info
by loody Dec. 20, 2011

Dec. 20, 2011

Dear all: is there any in formations I can get such as 1. when the last time the kthread running. 2. is the kthread alive? from the proc? -- Thanks for your help,

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Snapshot implementation on ext4 filesystem and fedora or redhat OS
by Swapnil Gaikwad Dec. 19, 2011

Dec. 19, 2011

What are the different design issues, documents,commands,system calls in kernel and user space? Is anyone have these details with running source code?

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Is there a way to build a cross reference with kernel file
by Jimmy Pan Dec. 18, 2011

Dec. 18, 2011

It seems we can use ctags, while, I don't really know how to implement it. I don't want to use the online cross reference every time... Thanks.

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Taking snapshot in ext4 filesystem
by Swapnil Gaikwad Dec. 18, 2011

Dec. 18, 2011

Hey, Anybody help me for theproject on taking snapshot of ext4 filesystem and related stuff... -- Regards, Swapnil Gaikwad.

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Kernel user communication mechanism
by rohan puri Dec. 16, 2011

Dec. 16, 2011

Hello Guys, I want to implement a kernel-user communication mechanism in which kernel can send events to user space (both blocking and non-blocking). Blocking events would require response which the kernel will interpret. Also user-space can also send the events to the kernel and get the response. Was having a look at the netlink sockets. What will be the behaviour for sending an event which is blocking on the response from user-space the queue is full. How this case will be handled. Also fanotify makes use of fsnotify's notification mechanism to send events and get response from kernel. Is it possible to send event from user-space to kernel space in -case of fanotify. I there any other way present which is better than these two above ways. Any ideas to implement a new mechanism are also appreciated. Regards, Rohan Puri

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Re: wrong core dump information
by solmac john Dec. 16, 2011

Dec. 16, 2011

Dear All, After recheck I found PID is different so same is possible kindly please ignore this thread. Thanks, John On Fri, Dec 16, 2011 at 12:28 PM, paladin tripathi < paladin.tripathi(a)gmail.com> wrote: > Dear All, > > I am using one SMP arm board if my one Application thread crash on one > core(CPU0) > and some time i observe second core generate(CPU1) the core dump. > > when i observed the core dump file i observe gdb is show CPU1 register > information. > > kernel crash messages:- > > Pid: 161, comm: thread > CPU: 1 Not tainted (2.6.35.13 #19) > PC is at 0x4002bb58 > LR is at 0x4002bb90 > pc : [<4002bb58>] lr : [<4002bb90>] psr: 20000010 > sp : 40b82de8 ip : 40043000 fp : 40b82fac > r10: 00000001 r9 : 43b8345c r8 : 00000000 > r7 : 00000001 r6 : 40b834e0 r5 : 00000001 r4 : 00000000 > r3 : 00000000 r2 : 00000001 r1 : 00000001 r0 : 00000000 > > (gdb) info reg > r0 0x1 1 > r1 0x0 0 > r2 0x0 0 > r3 0x1 1 > r4 0x0 0 > r5 0xf 15 > r6 0x0 0 > r7 0xf 15 > r8 0xbeeb8878 3203106936 > r9 0x0 0 > r10 0x40025000 1073893376 > r11 0xbeeb88b4 3203106996 > r12 0x4002ce44 1073925700 > sp 0xbeeb8870 0xbeeb8870 > lr 0x8714 34580 > pc 0x4002ce44 0x4002ce44 > fps 0x0 0 > cpsr 0x60000010 1610612752 > > > Is this expected behavior ? > > Is there any ARM patch which can prevent this ? > > Thanks, > Paladin >

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wrong core dump information
by solmac john Dec. 16, 2011

Dec. 16, 2011

Dear All, I am using one SMP arm board if my one Application thread crash on one core(CPU0) and some time i observe second core generate(CPU1) the core dump. when i observed the core dump file i observe gdb is show CPU1 register information. kernel crash messages:- Pid: 161, comm: thread CPU: 1 Not tainted (2.6.35.13 #19) PC is at 0x4002bb58 LR is at 0x4002bb90 pc : [<4002bb58>] lr : [<4002bb90>] psr: 20000010 sp : 40b82de8 ip : 40043000 fp : 40b82fac r10: 00000001 r9 : 43b8345c r8 : 00000000 r7 : 00000001 r6 : 40b834e0 r5 : 00000001 r4 : 00000000 r3 : 00000000 r2 : 00000001 r1 : 00000001 r0 : 00000000 (gdb) info reg r0 0x1 1 r1 0x0 0 r2 0x0 0 r3 0x1 1 r4 0x0 0 r5 0xf 15 r6 0x0 0 r7 0xf 15 r8 0xbeeb8878 3203106936 r9 0x0 0 r10 0x40025000 1073893376 r11 0xbeeb88b4 3203106996 r12 0x4002ce44 1073925700 sp 0xbeeb8870 0xbeeb8870 lr 0x8714 34580 pc 0x4002ce44 0x4002ce44 fps 0x0 0 cpsr 0x60000010 1610612752 Is this expected behavior ? Is there any ARM patch which can prevent this ? Thanks, John

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(no subject)
by Swapnil Gaikwad Dec. 16, 2011

Dec. 16, 2011

Hi , Tell me procedure or system call for- How to copy metadata of all files in a ext4 filesystem. -- Regards, Swapnil Gaikwad.

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why no vsyscall support on x86 or i386 ?
by Fredrick Dec. 16, 2011

Dec. 16, 2011

Hi, Why there is no vsyscall support on i386? I see it only on x86_64. In x86_64 it supports gettimeofday, etc. In i386, it only uses to support the sysenter optimization. Why there is no support for gettimeofday in i386 as a vsyscall? -Fredrick

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Why is the xadd instruction used to get atomic operation?
by Parmenides Dec. 15, 2011

Dec. 15, 2011

Hi, xadd is used in atomic function atomic_add_return() like this: 188static __inline__ int atomic_add_return(int i, atomic_t *v) 189{ 190 int __i; ... ... ... 195 /* Modern 486+ processor */ 196 __i = i; 197 __asm__ __volatile__( 198 LOCK "xaddl %0, %1;" 199 :"=r"(i) 200 :"m"(v->counter), "0"(i)); 201 return i + __i; 202 ... ... ... 211} The xadd will store v->counter into i, and store v->counter+i into v->counter. I wonder why we bother to obtain v->counter atomically. I try to modify the asm with the following code: static __inline__ int atomic_add_return(int i, atomic_t *v) { __asm__ __volatile__( LOCK "addl %1, %0;" : "m"(v->counter) : "=r"(i), "m"(v->counter)); return v->counter; } Does my code may cause some problems concerning atomic operation?

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